Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Minoru Nishida Last modified date:2019.12.24

Professor / Materials Physics and Engineering, Crystal Physics and Engineering / Department of Advanced Materials Science and Engineering / Faculty of Engineering Sciences


Papers
1. Fumiyoshi Yamashita, Yasunori Ide, Suguru Kato, Kyosuke Ueda, Takayuki Narushima, Sumio Kise, Kouji Ishikawa, Minoru Nishida, Effect of nonmetallic inclusions on fatigue properties of superelastic ti-ni fine wire, Metals, 10.3390/met9090999, 9, 9, 2019.09, This study investigated the effects of the types and length of nonmetallic inclusions on fatigue properties in rotating bending fatigue testing of Ti-Ni alloy fine wire. It was fabricated to include titanium carbides Ti(C,O) and titanium oxides Ti4 Ni2 Ox as either single phases or a mixture of both phases as nonmetallic inclusions in Ti-Ni alloy. The fatigue strength of Ti-Ni alloy depended on the number of nonmetallic inclusions of a length of ≥2 µm. Compared with Ti(C,O), Ti4 Ni2 Ox is coarse. It also exhibited a trend of readily forming particles and void assemblies, which are a defect morphology that originates from nonmetallic inclusions and readily act as crack origins of fatigue fractures..
2. Shota Hisada, Mitsuhiro Matsuda, Minoru Nishida, Carlo Alberto Biffi, Ausonio Tuissi, Microstructure and martensitic transformation behavior in thermal cycled equiatomic CuZr shape memory alloy, Metals, 10.3390/met9050580, 9, 5, 2019.05, Equiatomic CuZr alloy undergoes a martensitic transformation from the B2 parent phase to martensitic phases (P21/m and Cm) below 150 °C. We clarified the effect of the thermal cycling on the morphology and crystallography of martensite in equiatomic CuZr alloy using a transmission electron microscopy. The 10th cycled specimens consisted of different multiple structures at the maximum temperature of differential scanning calorimetry (DSC) measurement −400 °C and 500 °C, respectively. At the maximum temperature 400 °C of DSC measurement, it is composed of the fine plate-like variants, and a lamellar eutectoid structure consisting of Cu10Zr7 and CuZr2 phases on the martensitic variant. Concerning the maximum temperature of 500 °C of DSC measurement, it is observed the martensitic structure and the lamellar structure in which the martensitic phase was completely eutectoid transformed. The formation of this lamellar eutectoid structure, due to thermal cycling leads to the shift of forward and reverse transformation peaks to low and high temperature side. In addition, new forward and reverse transformation peaks indicating a new transformation appeared by thermal cycling, and the peaks remained around −20 °C. This new martensitic transformation behavior is also discussed..
3. Kazuki Tonotsuka, Yoshikazu Todaka, Nozomu Adachi, Motohiro Horii, Kenichi Toda, Masatoshi Mitsuhara, Masumi Iwasaki, Yoshinori Shiihara, Yoshitaka Umeno, Minoru Nishida, Hideharu Nakashima, Effect of lattice defects on tribological behavior for high friction coefficient under TCP added PAO lubrication in nanostructured steels, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.TETSU-2018-043, 105, 2, 160-167, 2019.02, Synopsis: The effect of lattice defects on the tribological behavior for high friction coefficient under tricresyl phosphate (TCP) added poly-α-olefin (PAO) lubrication was investigated in the nanostructured steels produced by heavy plastic deformation processes. In the surface-nanostructured SUJ2 bearing steel, the tribological behavior with high friction coefficient was observed in the ball-on-disk tests in comparison with the non-deformed steel. In addition, the similar phenomenon was observed in the ultra-low carbon (ULC) steel with high-density of lattice defects (grain boundary, dislocation and so on). By increasing the density of lattice defects, higher friction coefficient was shown. The reason of the tribo-logical behavior with high friction coefficient seems that the compound film of Fe-O-P system formed in the ball-on-disk test was worn..
4. K. Yamamoto, R. Noguchi, M. Mitsuhara, M. Nishida, T. Hara, D. Wang, H. Nakashima, Wide range control of Schottky barrier heights at metal/Ge interfaces with nitrogen-contained amorphous interlayers formed during ZrN sputter deposition, Semiconductor Science and Technology, 10.1088/1361-6641/aae4bd, 33, 11, 2018.10, A ZrN contact on a Ge substrate can alleviate the intrinsic Fermi-level pinning (FLP) position toward conduction band edge, which is induced by an amorphous interlayer (a-IL) containing nitrogen atoms at the interfaces. Since the a-IL could be retained on the Ge surface, we demonstrated a wide range Schottky barrier height (SBH) control for metal/a-IL/Ge contacts. The sputtering power for ZrN affects the SBH, pinning factor (S), and effective charge neutral level. A high S value of 0.26 was achieved, which is comparable to that of metal/Si contacts. A model was proposed for explaining the mechanism of this effective FLP alleviation..
5. Mitsuhiro Matsuda, Tomohiro Nishiura, Takateru Yamamuro, Minoru Nishida, Phase diagram of near equiatomic Zr-Pd alloy, Metals, 10.3390/met8050366, 8, 5, 2018.05, The exact eutectoid and peritectoid temperatures in near equiatomic Zr-Pd compositions have been determined by using the diffusion couple method and microstructure analysis. The crystal structure of Zr13Pd12 compound were estimated to be orthorhombic with a = 1.78 nm, b = 0.80 nm and c = 1.00 nm from the electron diffraction experiments. The Zr13Pd12 compound is formed at 1100 ± 2 K with a peritectoid reaction between Zr2Pd and ZrPd compounds. The ZrPd compound transforms to Zr13Pd12 and Zr9Pd11 compounds by a eutectoid reaction at 1028 ± 4 K. Based on these results, the phase diagram of near equiatomic Zr-Pd binary system is reconstructed..
6. Mitsuhiro Matsuda, Yoshimasa Shinagawa, Kazuki Takashima, Masatoshi Mitsuhara, Minoru Nishida, Characterization of Antiphase Boundary-Like Structure of B33 Martensite in ZrCoPd Alloy, Materials Transactions, 10.2320/matertrans.M2018146, 59, 10, 1567-1573, 2018.01, The antiphase boundary (APB)-like structure of B33 martensite in a ZrCoPd alloy was investigated by means of conventional transmission electron microscopy and high-Angle annular dark-field scanning transmission electron microscopy. The APB-like structure had atomic shifts along both the c-Axis on the (010)
B33
basal plane and the b-Axis on the (001)
B33
plane. The displacement vector of the APB-like structure could be expressed as R = (0, 1/4, =)
B33
The formation mechanism of the APB-like structure was also elucidated..
7. Rina Takizawa, Hiroshi Akamine, Masaru Itakura, Minoru Nishida, Nobuhiro Katayama, Koichiro Morimoto, Influence of desorption recombination temperatures on microstructure and coercivity of HDDR-processed anisotropic Nd-Fe-B magnet powders, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.J2017061, 82, 4, 121-124, 2018.01, In the hydrogenation decomposition desorption recombination(HDDR)processed Nd Fe Co B Al Ga Zr magnet powders, influence of the desorption recombination(DR)temperatures on the microstructures was investigated by high resolution scanning electron microscopy and scanning transmission electron microscopy. By applying the DR treatment under high vacuum(DR Step 2)at relative low temperatures about 973 K, we can obtain the excellent texture in which the average size of Nd2Fe14B grains is refined to about 240 nm and the grain boundary(GB)phase is uniformly dispersed around the Nd2Fe14B grains. In the GB phase, furthermore, the Nd composition increases and the(Fe, Co)composition decreases drastically with decreasing the DR temperatures, and then Nd rich GB phase with more than 65 at.%Nd can be formed at 973 K. At 973 K, however, the region with unformed GB phase is remained about 10% of the specimen, which leads to deterioration of the coercivity. It was found that the gently DR treatment is very effective not only for increasing the coercivity but also for improving the squareness in demagnetization curve..
8. D. Schryvers, E. K.H. Salje, Minoru Nishida, A. De Backer, H. Idrissi, S. Van Aert, Quantification by aberration corrected (S)TEM of boundaries formed by symmetry breaking phase transformations, Ultramicroscopy, 10.1016/j.ultramic.2016.12.022, 176, 194-199, 2017.05, The present contribution gives a review of recent quantification work of atom displacements, atom site occupations and level of crystallinity in various systems and based on aberration corrected HR(S)TEM images. Depending on the case studied, picometer range precisions for individual distances can be obtained, boundary widths at the unit cell level determined or statistical evolutions of fractions of the ordered areas calculated. In all of these cases, these quantitative measures imply new routes for the applications of the respective materials..
9. Takanori Ito, Shigeto Yamasaki, Masatoshi Mitsuhara, Minoru Nishida, Mitsuharu Yonemura, Effect of intergranular carbides on creep strength in nickel-based heat-resistant alloys, Materials Transactions, 10.2320/matertrans.M2016291, 58, 1, 52-58, 2017.01, Creep behaviors and microstructures for two Ni-based heat-resistant alloys with different carbon contents were investigated. The chemical compositions of the alloys were Ni-20Cr-15Co-6Mo-1Ti-2Al-2Nb-0.004 and 0.021C (mass%). The 0.004C and 0.021C alloys are referred to as the low-and high-C alloys, respectively. After solid-solution treatment at 1373 K for 1 h and isothermal annealing at 1023 K for 32 h, fine Ni3Al (γ) particles were formed in the grain interior of both alloys. The average diameter and number density of γ particles were similar in both alloys. M23C6 carbides were formed on grain boundaries after the isothermal annealing. Coverage ratios with the carbides in the high-C alloy were higher than that in the low-C alloys. Creep tests were performed at 1123 K and 130 MPa. The rupture time for the high-C alloy was longer than that for the low-C alloy, though both minimum creep rates were similar. In the high-C alloy, the creep strain was stored uniformly in the grain interior and the formation of a precipitate-free zone during the creep deformation was suppressed. Therefore, intergranular carbides with a high coverage ratio decreased the creep rate in the acceleration region..
10. Takanori Ito, Shigeto Yamasaki, Masatoshi Mitsuhara, Hideharu Nakashima, Minoru Nishida, Mitsuharu Yonemura, Microstructure and creep property in polycrystalline Ni-based alloy with intergranular intermetallics, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.TETSU-2016-107, 103, 7, 434-442, 2017.01, Creep properties and microstructures for a polycrystalline Ni-based heat-resistant alloy whose grain boundaries were covered by dense intergranular intermetallics were investigated. Creep tests were carries out at 850°C and 80-130 MPa. The creep strength of this alloy was higher than the Alloy617 and HR6W, and equal to the Alloy740, which are pre-existing candidate materials for steam pipes of A-USC power plant. The retardation of acceleration of creep rate was observed characteristically in the creep curves. This retardation behavior was deeply related to the superior creep strength of this alloy. The spherical Ni3Al (γ') particles were distributed uniformly in the grain interior, whose coarsening behavior was monotonically dependent on the creep time. The intermetallics of Laves phase and s pahse were formed densely at grain boundary. High coverage ratio of the intergranular intermetallics was maintained until the later stage of acceleration creep region. Therefore, it suggested that the retardation of creep acceleration was not caused by the precipitates behavior of intragranular γ' particles and intergranular intermetallics, though both the precipitates were understandably effective against the creep strengthening. The plate-like Laves phase was formed in the grain interior during creep. The evolution of volume fraction of intragranular Laves phase depended on not creep time but creep strain. From the results of SEM/EBSD analyses and TEM observations, it revealed that the intragranular Laves phase enhanced the work-hardenability due to the constraint on plasticity and originated the retardation of creep acceleration..
11. Masaru Itakura, Shin ichi Murayama, Masatoshi Mitsuhara, Minoru Nishida, Hiroaki Koga, Masaki Nakano, Hirotoshi Fukunaga, Microstructures of Ta-inserted SmCo5/Fe nanocomposite thick film magnets, Materials Transactions, 10.2320/matertrans.M2017035, 58, 10, 1351-1355, 2017.01, Ta-inserted SmCo5/Fe nanocomposite thick film magnets were synthesized by high-speed pulsed laser deposition followed by pulse annealing. The microstructures of the film magnets were characterized by high-resolution scanning electron microscopy and scanning transmission electron microscopy. The as-deposited thick film possessed a multilayered Sm-Co/Ta/α-Fe/Ta structure with amorphous Sm-Co layers and [110]-oriented crystalline α-Fe layers. After pulse annealing, many fine grains of Laves phase TaCo2 were formed, and then the multilayered structure was converted to a granular nanocomposite thick film magnet composed of fine crystalline grains of Sm(Co, Fe)5, α-(Fe, Co), and TaCo2. The volume fractions and grain sizes of hard magnetic Sm(Co, Fe)5, soft magnetic α-(Fe, Co), and TaCo2 were controlled by the thicknesses of the Ta layer, producing a nanocomposite thick film magnet with good exchange coupling..
12. Fumiya Watanabe, Zeid A. Nima, Takumi Honda, Masatoshi Mitsuhara, Minoru Nishida, Alexandru S. Biris, X-ray photoelectron spectroscopy and transmission electron microscopy analysis of silver-coated gold nanorods designed for bionanotechnology applications, Nanotechnology, 10.1088/1361-6528/28/2/025704, 28, 2, 2017.01, Multicomponent nano-agents were designed and built via a core-shell approach to enhance their surface enhanced Raman scattering (SERS) signals. These nano-agents had 36 nm ×12 nm gold nanorod cores coated by 4 nm thick silver shell films and a subsequent thin bifunctional thiolated polyethylene glycol (HS-PEG-COOH) layer. Ambient time-lapsed SERS signal measurements of these functionalized nanorods taken over a two-week period indicated no signal degradation, suggesting that large portions of the silver shells remained in pure metallic form. The morphology of the nanorods was characterized by transmission electron microscopy (TEM) and ultra-high resolution scanning TEM. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were utilized to assess the oxidation states of the silver shells covered by HS-PEG-COOH. The binding energies of Ag 3d XPS spectra yielded very small chemical shifts with oxidation; however, the AES peak shapes gave meaningful information about the extent of oxidation undergone by the nano-agent. While the silver shells without HS-PEG-COOH coatings oxidized significantly, the silver shells with HS-PEG-COOH remained predominantly metallic. In fact, six month-old samples still retained mostly metallic silver shells. These findings further demonstrate the stability and longevity of the nanostructures, indicating their significant potential as plasmonically active agents for highly sensitive detection in various biological systems, including cancer cells, tissues, or even organisms..
13. Hiroshi Akamine, So Okumura, Sahar Farjami, Yasukazu Murakami, Minoru Nishida, Imaging of surface spin textures on bulk crystals by scanning electron microscopy, Scientific reports, 10.1038/srep37265, 6, 2016.11, Direct observation of magnetic microstructures is vital for advancing spintronics and other technologies. Here we report a method for imaging surface domain structures on bulk samples by scanning electron microscopy (SEM). Complex magnetic domains, referred to as the maze state in CoPt/FePt alloys, were observed at a spatial resolution of less than 100 nm by using an in-lens annular detector. The method allows for imaging almost all the domain walls in the mazy structure, whereas the visualisation of the domain walls with the classical SEM method was limited. Our method provides a simple way to analyse surface domain structures in the bulk state that can be used in combination with SEM functions such as orientation or composition analysis. Thus, the method extends applications of SEM-based magnetic imaging, and is promising for resolving various problems at the forefront of fields including physics, magnetics, materials science, engineering, and chemistry..
14. M. Matsuda, R. Sago, K. Akamine, S. Tsurekawa, K. Takashima, Minoru Nishida, Enhancement of ductility in Fe-Co based alloys by substitution of Pd, Journal of Alloys and Compounds, 10.1016/j.jallcom.2016.04.275, 682, 124-131, 2016.10, We investigated the relationship between the microstructure and mechanical properties of the ternary Co50Fe50-xPdx alloys with different Pd content. Co50Fe45Pd5, Co50Fe40Pd10 and Co50Fe35Pd15 alloys annealed at 873 K were composed of the α'-matrix having a B2 structure with a high degree of order and two kinds of Fe-Co-Pd precipitates with L10 and L12 structures, which formed at the grain boundaries and in the grain interior. The 0.2% proof stress, tensile strength, hardness and elongation were increased by substituting Pd for Fe in Co-Fe-Pd alloy. It is noteworthy that the Co50Fe40Pd10 alloy had a high tensile strength of 1293 MPa and high total elongation of 12% on average. The significant improvement in the ductility of the Co50Fe40Pd10 alloy is attributed to the ductile Fe-Co-Pd phase that precipitates at the grain boundaries and in the α′-grain interior. The ductile precipitates suppressed the intergranular and cleavage fracture. The increase in strength of Co50Fe50-xPdx alloys is likely to come from both the precipitation hardening and the grain refinement of the α′-matrix..
15. Shunichi Motomura, Toru Hara, Toshihiro Omori, Ryosuke Kainuma, Minoru Nishida, Morphological and chemical analysis of bainite in Cu-17Al-11Mn (At.%) alloys by using orthogonal FIB-SEM and double-EDS STEM, Microscopy, 10.1093/jmicro/dfw003, 65, 3, 243-252, 2016.06, In this study, new microscopy techniques were developed for understanding the mechanism for the bainitic transformation in a Cu-17Al-11Mn (at%) alloy. An orthogonally arranged focused ion beam and a scanning electron microscope were employed to observe three-dimensional (3D) morphology of the bainite phase, in addition to compositional analysis by using a scanning transmission electron microscope equipped with a double-detector energy-dispersive X-ray spectrometer system. The 3D morphology of these samples was observed at different aging times and aging temperatures; the results obtained indicated that with increasing aging time and/or aging temperature, the bainite phase at the initial stage of formation exhibits a plate-like shape, which changes to a lenticular form. A habit plane was uniquely determined as ∼{9 3 2} by the combination of 3D image reconstruction and an electron back-scattered diffraction technique. The compositional analysis revealed the spatial distribution of the compositional variation between the bainite and matrix phases in the initial stages of the transformation. In the bainite phase, the Cu concentration was higher, while the concentrations of Al and Mn were lower than those in the surrounding matrix, indicative of the diffusion of the constituent elements with the growth of the bainite phase..
16. Masatoshi Mitsuhara, Tomoya Masuda, Minoru Nishida, Tomonori Kunieda, Hideki Fujii, Precipitation Behavior During Aging in α Phase Titanium Supersaturated with Cu, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-016-3344-7, 47, 4, 1544-1553, 2016.04, Age hardening of Ti-2.3 mass pct Cu (Ti-2.3Cu) at 673 K to 873 K (400 °C to 600 °C) after solution treatment at 1063 K (790 °C) was observed. The relationship between precipitates formed during aging and changes in hardness was investigated. During aging at 673 K (400 °C), the hardness increased rapidly up to 200 hours, and subsequently increased more slowly up to 1000 hours. At 873 K (600 °C), the hardness began to decrease immediately. Transmission electron microscopy showed that fine disk-shaped precipitates of 20 to 40 nm in diameter grew in the α phase. It is concluded that these precipitates interacted with dislocations and increased the hardness. At 873 K (600 °C), precipitates of 1 µm in length and Ti
2
Cu particles of 200 nm in length were observed. The decrease in hardness may have resulted from the precipitate formation decreasing the concentration of Cu in the α phase. Bright/dark contrast of the three atomic layers and small atomic shift of the hcp structure were observed in the atomic resolution imaging of the precipitates. This suggests that the precipitates are not just Cu-enriched zones and have structures with similar periodicity to the Ti
2
Cu phase, which is thermally stable at those aging temperatures..
17. Shunichi Motomura, Yohei Soejima, Takayuki Miyoshi, Toru Hara, Toshihiro Omori, Ryosuke Kainuma, Minoru Nishida, In situ heating SEM observation of the bainitic transformation process in Cu–17Al–11Mn (at.%) alloys, Microscopy, 10.1093/jmicro/dfv363, 65, 2, 159-168, 2016.04, To understand the bainitic transformation behavior in Cu–17Al–11Mn (at.%) alloys, dynamic in situ observation during heating was carried out in a scanning electron microscope (SEM). In this study, after optimizing the sample preparation method and observation conditions, we successfully observed the transformation process with sufficient resolution and contrast. From the observation results, bainite is first formed preferentially at the grain boundaries of the parent phase. Bainite is also formed inside the grains to relax the elastic strain generated by the initial bainite. Regarding the growth mode, in the early stage of the transformation, bainite grows along the longitudinal direction, and in the late stage, it grows along the lateral direction. The growth rate of the bainite was also evaluated by continuous observation of the same plate. Dynamic in situ observation of a martensitic transformation in the same alloy was also performed to compare the growth mode with that of bainite, and it was found that the behavior is considerably different between bainitic and the martensitic transformations..
18. Masatoshi Mitsuhara, Shigeto Yamasaki, Masaki Miake, Hideharu Nakashima, Minoru Nishida, Junichi Kusumoto, Akihiro Kanaya, Creep strengthening by lath boundaries in 9Cr ferritic heat-resistant steel, Philosophical Magazine Letters, 10.1080/09500839.2016.1154200, 96, 2, 76-83, 2016.02, The interactions between dislocations and lath boundaries in Grade 91 steel were observed by an in situ transmission electron microscopy tensile test at 973 K. Dislocations glided slowly and bowed out in a martensite lath interior. The ends of the dislocation were connected to the lath boundaries. In a tempered specimen, the pinning stress caused by the lath boundary was estimated to be >70 MPa with a lath width of 0.4 m. In crept specimens, lath coarsening reduced the pinning effect..
19. Mitsuhiro Matsuda, Masatoshi Mitsuhara, Kazuki Takashima, Minoru Nishida, Antiphase boundary-like structure of B19 martensite in Ti-Ni-Pd shape memory alloy, Materials Transactions, 10.2320/matertrans.MB201505, 57, 3, 250-256, 2016.01, The antiphase boundary (APB)-like structure of B19 martensite in the Ti-Ni-Pd alloy was investigated by means of conventional transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy. Some APB-like structures with wide and curved contrast exhibited shifts along the (010)B19 and (001)B19 planes; that is, it exhibited facets composed of those planes at the atomic level. This atomic displacement reflects the atomic movement stemming from not only martensitic but also a kind of R-phase transformations..
20. Hiroshi Akamine, Masatoshi Mitsuhara, Minoru Nishida, Developments of coal-fired power plants
Microscopy study of Fe-Ni based heat-resistant alloy for efficiency improvement, Evergreen, 3, 2, 45-53, 2016.01, Anthropogenic emissions of greenhouse gases are one of the possible reasons for the global warming. Coal consumption is predicted to be increased over several decades due to increasing demands in some countries. In the medium-term energy strategy, coal-fired power plants thus need to be developed. For this purpose, developments of new heat-resistant alloys that can stand severe steam conditions in advanced power plants are essential. A potential alloy was studied, which revealed that hardness of the alloy is related to the distribution of precipitates. The development of the alloy is also vital to make the power plants more economically competitive..
21. Y. Soejima, S. Motomura, Masatoshi Mitsuhara, T. Inamura, Minoru Nishida, In situ scanning electron microscopy study of the thermoelastic martensitic transformation in Ti-Ni shape memory alloy, Acta Materialia, 10.1016/j.actamat.2015.10.017, 103, 352-360, 2016.01, The thermoelastic martensitic transformation from the B2 to B19′ structures in the Ti-Ni shape memory alloy was observed by in situ scanning electron microscopy in order to investigate the self-accommodation microstructure. Nucleation of the V-shaped habit plane variant cluster (2HPVC) triggers the formation of the hexangular HPVC (6HPVC) that is formed by six habit plane variants in the grain interior. The triangular morphology (3HPVC) is a derivative of 2HPVC. The autocatalytic transformation spreads from the 6HPVCs to the grain boundary and the reverse transformation proceeds like a rewind of the forward transformation. 2HPVC and 6HPVC are the most favorable morphologies for nucleation and growth, respectively, as explained by the analysis of the kinematic compatibility at junction planes..
22. C. A. Biffi, M. Coduri, H. Yoshida, Y. Soejima, Minoru Nishida, A. Tuissi, The effect of thermal cycling on the martensitic transformation in equiatomic CuZr shape memory alloy, Journal of Alloys and Compounds, 10.1016/j.jallcom.2015.09.022, 653, 591-595, 2015.12, This work highlights the lack of stability of the martensitic transformation (MT) upon thermal cycling of equiatomic CuZr shape memory alloy (SMA). The initial MT taking place at high temperature is inhibited within 10 thermal cycles, whilst a low temperature transformation (at -20 °C) is established. The MT evolution is observed through DSC and XRD measurements and SEM observations. Its reversible character and the limited thermal hysteresis suggest a new low-temperature MT in CuZr intermetallic SMA compound..
23. Hiroshi Akamine, K. H.W. Van Den Bos, N. Gauquelin, S. Farjami, S. Van Aert, D. Schryvers, Minoru Nishida, Determination of the atomic width of an APB in ordered CoPt using quantified HAADF-STEM, Journal of Alloys and Compounds, 10.1016/j.jallcom.2015.04.205, 644, 570-574, 2015.05, Anti-phase boundaries (APBs) in an ordered CoPt alloy are planar defects which disturb the ordered structure in their vicinity and decrease the magnetic properties. However, it has not yet been clarified to what extend the APBs disturb the ordering. In this study, high-resolution HAADF-STEM images are statistically analysed based on the image intensities estimated by the statistical parameter estimation theory. In the procedure, averaging intensities, fitting the intensity profiles to specific functions, and assessment based on a statistical test are performed. As a result, the APBs in the stable CoPt are found to be characterised by two atomic planes, and a contrast transition range as well as the centre of an inclined APB is determined. These results show that the APBs are quite sharp and therefore may have no notable effect on the net magnetic properties due to their small volume fraction..
24. M. Matsuda, S. Nishimura, S. Tsurekawa, K. Takashima, Masatoshi Mitsuhara, Minoru Nishida, Crystallography and morphology of antiphase boundary-like structure induced by martensitic transformation in Ti-Pd-Fe alloy, Journal of Alloys and Compounds, 10.1016/j.jallcom.2014.08.258, 618, 527-532, 2015.01, The antiphase boundary (APB)-like structure of both 9R and B19 martensites in the Ti-Pd-Fe alloy was investigated by means of transmission electron microscopy. Some APB-like structures with curved and wide contrasts along the (0 0 1)9Rbasal plane are observed in 9R martensitic plates. The atomic displacement on the APB-like structure reflects the atomic movement stemming from the microdomains formed as a pre-martensitic transformation. The displacement vector of the APB-like structure in the B19 martensite can be expressed as R = 〈1/3 0 -1/2〉B19. The density of APB-like contrasts increases by the substitution of Fe for Pd in Ti-Pd-Fe alloy..
25. Shigeru Hirata, Takanori Ito, Masatoshi Mitsuhara, Minoru Nishida, Effect of cold-working and Mo addition on creep behavior in high Mn austenitic stainless steels, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.101.51, 101, 1, 51-58, 2015.01, The effect of cold-working and Mo addition on creep behavior in 15Mn-17Cr-0.09C-0.39N-(0.01, 0.5, 1.0, 1.5, 2.0) Mo steels has been investigated. The steels with solution treatment at 1373 K and ones with 40% cold-rolling are subjected to a creep test at 873 K under 200-400 MPa, respectively. Time to rupture (tr) of both steels increases with increasing the Mo concentration. Since tr in the cold-rolled steels is shorter then that in solution-treated ones in a same creep condition, cold-working is suggested to be harmful for creep strength. Creep rate in a primary creep region of cold-rolled steels with more than 1.0 Mo is smaller than that for solution-treated ones because many dislocations are induced by the cold-working. This nature is advantageous as sealing materials for high temperature. Mo addition causes decreasing of minimum creep rate in the solution-treated steels. A linear relationship exists between logarithm of minimum creep rate and Mo content. In the cold-rolled steels with 0.01 Mo and 0.5 Mo, recrystallization is partially occurred during a prescribed heat treatment before the creep tests. Therefore, the creep rate is promptly accelerated. In the cold-rolled steels with more than 1.0 Mo, the suppression of recrystallization by Mo yields the small minimum creep rate and the extension of tr. Fine precipitates of Laves phase are generated in grain interior in tertiary creep region of cold-rolled steels with 1.5 and 2.0 Mo. It also contributes to the extension of tr due to the retarding effect of creep rate acceleration..
26. Keisuke Yamamoto, Ryutaro Noguchi, Masatoshi Mitsuhara, Minoru Nishida, Toru Hara, Dong Wang, Hiroshi Nakashima, Electrical and structural properties of group-4 transition-metal nitride (TiN, ZrN, and HfN) contacts on Ge, Journal of Applied Physics, 10.1063/1.4930573, 118, 11, 2015.01, Electrical and structural properties were investigated for group-4 transition-metal nitride contacts on Ge (TiN/Ge, ZrN/Ge, and HfN/Ge), which were prepared by direct sputter depositions using nitride targets. These contacts could alleviate the intrinsic Fermi-level pinning (FLP) position toward the conduction band edge. It was revealed that this phenomenon is induced by an amorphous interlayer (a-IL) containing nitrogen atoms at the nitride/Ge interfaces. The strength of FLP alleviation positively depended on the thickness of a-IL. TiN/Ge and ZrN/Ge contacts with ∼2 nm-thick a-ILs showed strong FLP alleviations with hole barrier heights (ΦBP) in the range of 0.52-56 eV, and a HfN/Ge contact with an ∼1 nm-thick a-IL showed a weaker one with a ΦBP of 0.39 eV. However, TaN/Ge contact without a-IL did not show such FLP alleviation. Based on the results of depth distributions for respective elements, we discussed the formation kinetics of a-ILs at TiN/Ge and ZrN/Ge interfaces. Finally, we proposed an interfacial dipole model to explain the FLP alleviation..
27. M. Matsuda, F. Tanaka, S. Tsurekawa, K. Takashima, Masatoshi Mitsuhara, Minoru Nishida, Novel long-period stacking-ordered structure of martensite in zirconium-cobalt-palladium alloys, Philosophical Magazine Letters, 10.1080/09500839.2014.995739, 95, 1, 21-29, 2015.01, A novel long-period stacking-ordered (LPSO) structure of a martensitic phase in a Zr-Co-Pd alloy was discovered and characterized by means of conventional transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy. The new phase had a 6O structure and its lattice parameters were estimated to be a = 0.34, b = 0.45 and c = 1.53 nm. The formation mechanism and the space group of the LPSO structure are described..
28. Yohei Soejima, Takayuki Miyoshi, Tomonari Inamura, Minoru Nishida, In-situ SEM observations of nucleation and growth of thermoelastic martensitic transformation in shape memory alloys, International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, PTM 2015 PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 649-650, 2015, The nucleation, growth, forward and reverse transformation processes of thermoelastic martensite (TM) in shape memory alloys have been investigated by in-situ SEM cooling and heating observations. The homogeneous-like nucleation from the grain interior was observed in Ti-Ni, Ti-Nb-Al, Ti-Ni-Pd alloys. On the other hand, the heterogeneous nucleation from the grain boundary was observed in Ni-Mn-Ga, Cu-Al-Mn, Cu-Al-Ni alloys. In addition, the microstructure memory effect (MME) of the M phase only occurs during thermal cycles in the Ti-Nb-Al alloy. It is suggested that there is intimate relation between the nucleation site and the distribution of elastic stress field due to the anisotropy of thermal expansion coefficient. It is assumed that the change of internal stress field in the parent (P) phase during transformation cycles prevents MME..
29. Hiroshi Akamine, Sahar Farjami, Hidetsugu Sakaguchi, Minoru Nishida, Phase-field simulation of magnetic field-induced preferential variant selection in A1-L10 disorder-order transformation, International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, PTM 2015 PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 425-426, 2015, Near-equiatomic Co-Pt, Fe-Pd and Fe-Pt alloys undergo cubic-tetragonal disorder-order transformation and form three orientation variants. It has been reported that magnetic fieldinduced preferential nucleation of one variant in the initial stage of ordering introduces preferential growth of the same variant in the later magnetic field-free stage [1]. In this study, the effect of preferential nucleation on microstructure evolution in the later stage is studied by phasefield method. The results indicate that the increase in fraction of preferential variant depends on nucleation ratio between the variants, and the stress field originated from the macroscopic shape deformation is the most possible factor affecting preferential growth in the later stage..
30. B. Karbakhsh Ravari, S. Farjami, Minoru Nishida, Effects of Ni concentration and aging conditions on multistage martensitic transformation in aged Ni-rich Ti-Ni alloys, Acta Materialia, 10.1016/j.actamat.2014.01.028, 69, 17-29, 2014.05, The effects of Ni concentration and aging conditions on the multistage martensitic transformation (MMT) in aged Ni-rich Ti-Ni alloys have been investigated by differential scanning calorimetry and in situ scanning electron microscopy. The effect of Ni concentration was evaluated using Ti-50.6, 50.8 and 51.0 at.% Ni alloys. These alloys were heat treated at 1223 K for 3.6 ks and then aged at 773 K for 3.6 ks. Although the triple-stage transformation appeared in the Ti-50.6 and 51 at.% Ni alloys during cooling, the transformation sequence of the two alloys was completely different. Quadruple-stage transformation was observed in the Ti-50.8 at.% Ni alloy. The characteristic microstructure responsible for the MMT in each of the aged alloys strongly depended on the degree of Ni supersaturation and the aging temperature and time. We have proposed and experimentally verified a general rule that explains the effects of Ni concentration and aging conditions on the microstructural changes and thus the MMT sequences. This will allow the MMT in Ni-rich Ti-Ni alloys to be controlled by selecting appropriate aging conditions..
31. Shigeru Hirata, Takanori Ito, Masatoshi Mitsuhara, Minoru Nishida, Effect of Mo on softening behavior during annealing in cold-rolled high Mn austenitic stainless steels, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.100.406, 100, 3, 406-413, 2014.03, The effect of molybdenum (Mo) on softening behavior of cold-rolled high manganese austenitic stainless steels was investigated. The high temperature hardness of cold-rolled Mo-free steel was drastically decreased by prolonged annealing at 873 K. On the other hand, there is not remarkable degradation of high temperature hardness in the steels containing more than 1 mass% Mo. Fully recrystallized structure is observed in Mo-free steel after annealing at 873 K for 1440 ks. Since deformation structures were not disappeared in the steels containing more than 1 mass% Mo even after annealing, the addition of Mo retarded the recrystallization in the work-hardening steels. After annealing, fine particles of M23C6 type carbide precipitated at the grain boundaries in the steel containing Mo. The amount of Mo in M 23C6 carbides was increased with increasing Mo content. On the other hand, the size of these carbides slightly decreased with increasing Mo content. These fine carbides strongly prevented the grain boundary movement (migration), therefore recrystallizaiton in the work-hardening steels was retarded. Moreover, the growth of M23C6 carbides at the grain boundary was consistent with Ostwald ripening equation substituted Mo for Cr. This result suggested that the growth rate of M23C6 was controlled by the diffusion of Mo..
32. Keisuke Yamamoto, Masatoshi Mitsuhara, Keisuke Hiidome, Ryutaro Noguchi, Minoru Nishida, Dong Wang, Hiroshi Nakashima, Role of an interlayer at a TiN/Ge contact to alleviate the intrinsic Fermi-level pinning position toward the conduction band edge, Applied Physics Letters, 10.1063/1.4870510, 104, 13, 2014.03, TiN/Ge contacts, prepared by direct sputter deposition from a TiN target, can alleviate the intrinsic Fermi-level pinning (FLP) position toward the conduction band edge. This work focuses on studying the origin of the FLP alleviation. Investigations on both the electrical properties and interfacial structures of TiN/Ge contacts showed that an amorphous interlayer (IL) containing nitrogen played an important role in the alleviation. For comparison, the properties of Ti/Ge contacts were also studied. Based on these results, the IL structure that induced the FLP alleviation was clearly shown and a model was proposed to explain the FLP alleviation..
33. M. Matsuda, R. Yamashita, S. Tsurekawa, K. Takashima, Masatoshi Mitsuhara, Minoru Nishida, Antiphase boundary-like structure of B19′ martensite via R-phase transformation in Ti-Ni-Fe alloy, Journal of Alloys and Compounds, 10.1016/j.jallcom.2013.10.015, 586, 87-93, 2014.01, The antiphase boundary (APB)-like structure of B19′ martensite via R-phase transformation in a Ti-Ni-Fe alloy was investigated by means of transmission electron microscopy. The APB-like structure exhibited shifts along the (0 1 0)B19′, (0 0 1)B19 , and (1 0 0)B19′ planes; that is, it exhibited facets composed of those planes at the atomic level. This atomic displacement reflects the atomic movement stemming from the R-phase transformation..
34. M. Matsuda, K. Yamashita, S. Tsurekawa, K. Takashima, Minoru Nishida, Ductility enhancement in Co-Fe-Ni alloys by microstructural control, Intermetallics, 10.1016/j.intermet.2014.04.004, 52, 124-130, 2014.01, We investigated the relationship between the microstructure and mechanical properties of ternary Co-Fe-Ni alloys. The solution-treated Co 50Fe40Ni10 alloy was composed of only the α′-phase having a B2 structure with a low degree of order, whereas the Co50Fe40Ni10 alloy annealed at 873 K consisted of a dual phase, i.e., an α′-matrix and a γ-phase with a face-centered cubic structure that primarily covered the grain boundaries of the α′-matrix and precipitated finely in the grain interior. The orientation relationship between the α′-matrix and the γ-phase is determined to be (11̄0)α′//(11̄1̄) γand [001]α′//[01̄1]γ, i.e., N-W relationship. The volume fraction of the γ-phase was estimated to be about 26%. Substituting Ni at 10 at% increased the yield, tensile strength, and total elongation. It is noteworthy that the Co50Fe40Ni10 alloy annealed at 873 K had a high tensile strength of 1005 MPa and high total elongation of over 12%. The origin of the dramatic improvement in the ductility is attributed to the considerably ductile γ-phase, which suppresses intergranular and cleavage fracture. High strengthening is also originated from both the solid-solution strengthening of Ni and the grain refinement of the α′-matrix..
35. Banafsheh Karbakhsh Ravari, Masatoshi Mitsuhara, Sahar Farjami, Minoru Nishida, Effect of thermal cycling on multistage martensitic transformation in aged ti-50.8 at% ni alloy, Materials Transactions, 10.2320/matertrans.M2013309, 54, 12, 2185-2188, 2013.12, The effect of thermal cycling on multistage martensitic transformation (MMT) in aged Ti-50.8 at% Ni alloy was investigated. The specimens were solution-treated at 1273 K for 3.6 ks and then aged at 773 K for 3.6 ks in vacuum without atmosphere regulation. Upon cooling the aged specimens clearly showed quadruple-stage transformation denoted as B2 → R → M1 → M2 → M3. The peak temperatures of exothermic reactions R M1 and M2(corresponding to the R-phase M1 and M2 transformations respectively) in the differential scanning calorimetry (DSC) cooling curve were rather stable up to 100 thermal cycles since there were fine Ti3Ni4 precipitates with high distribution density in the intermediate and grain boundary regions. These precipitates prevented the formation of dislocations during thermal cycling. On the other hand the peak temperature of exothermic reaction M3 (corresponding to the M3 transformation) drastically decreased with increasing the number of thermal cycles since there were large Ti 3Ni4 precipitates with low distribution density. Many dislocations were observed in the central regions of grains after 100 thermal cycles..
36. E. Okunishi, T. Kawai, Masatoshi Mitsuhara, S. Farjami, Masaru Itakura, T. Hara, Minoru Nishida, HAADF-STEM studies of athermal and isothermal ω-phases in β-Zr alloy, Journal of Alloys and Compounds, 10.1016/j.jallcom.2011.12.115, 577, SUPPL. 1, 2013.11, We have succeeded in direct observation of the atomic arrangement in athermal and isothermal ω-phases in Zr-7.5 at.% Nb alloy by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), although the atomic displacement along 〈0 0 0 1〉 has not been determined quantitatively. The orientation relationship between ω- and β-phases is visualized on atomic scale..
37. Shuichi Miyazaki, Tomoyuki Kakeshita, Minoru Nishida, Proceedings of the international conference on martensitic transformations (ICOMAT-2011), Journal of Alloys and Compounds, 10.1016/j.jallcom.2013.07.056, 577, SUPPL. 1, 2013.11.
38. B. Karbakhsh Ravari, N. Kizakibaru, Minoru Nishida, Quantitative microstructure analyses upon multistage martensitic transformation in an aged Ti-50.8 at.% Ni alloy, Journal of Alloys and Compounds, 10.1016/j.jallcom.2012.03.041, 577, SUPPL. 1, 2013.11, Quantitative microstructure analyses upon multistage martensitic transformation (MMT) in an aged Ti-50.8 at.% Ni alloy have been performed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). The alloy used was heat-treated at 1273 K for 3.6 ks and then aged at 773 K for 3.6 ks under regulated and unregulated atmospheres. The specimen heat-treated under the regulated atmosphere shows the single stage martensitic transformation in addition to the R-phase transformation. That is, B2 → R → M. On the other hand, the specimen heat-treated under the unregulated atmosphere shows the MMT with the sequence of B2 → R → M1 → M2 → M3. There are three exothermic peaks related to the martensitic transformation in addition to the R-phase transformation peak. The R-phase transformation takes place at the intermediate part of grains and around the grain boundaries. Subsequently, the first (M1) and second (M2) martensitic transformations occur at the intermediate part of grains and around the grain boundaries, respectively. Finally, the third transformation (M3) appears at the center part of grains directly from the B2 phase without via the R-phase transformation. The proposed transformation sequence is quantitatively proved by comparing the EBSD image with DSC curve..
39. Hiroshi Akamine, Sahar Farjami, Masatoshi Mitsuhara, Minoru Nishida, Takashi Fukuda, Tomoyuki Kakeshita, Electron microscopy study of preferential variant selection in copt alloy ordered under a magnetic field, Materials Transactions, 10.2320/matertrans.MAW201313, 54, 9, 1715-1718, 2013.09, Transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) observations were carried out to investigate microstructure formation and variant selection process in L10-type ordered CoPt alloy upon a two-step ordering heat-treatment. The first step corresponds to nucleation process carried out under a magnetic field of 10 T and the second step represents growth process without magnetic field. After the first step of ordering, ordered domains of about 5 nm in size were observed and fraction of the preferred variant with the c-axis parallel to applied magnetic field was slightly higher than that of the other two variants. Formation of tweed microstructure along {011}L10 was confirmed at the initial stage of ordering. This structure is considered to be derived from the periodic alignment of interface between two ordered variants with twin relation. At the early stage of the second step of ordering, numerous micro-twins were formed through tweed microstructure and the volume fraction of the preferred variant was increased accompanying with modulation of twins, while that of other two variants was decreased. After the second step of ordering, the twins were vanished and single variant was obtained..
40. B. Karbakhsh Ravari, Minoru Nishida, In situ SEM studies of the transformation sequence of multistage martensitic transformations in aged Ti-50.8 at.% Ni alloys, Philosophical Magazine, 10.1080/14786435.2013.769070, 93, 18, 2279-2296, 2013.06, The transformation behaviour of the multistage martensitic transformation in aged Ti-50.8 at.% Ni alloys was investigated by differential scanning calorimetry (DSC) and in situ scanning electron microscopy (SEM). The specimens aged from 673 to 748 K for 3.6 ks under an unregulated heat treatment atmosphere exhibited the double-stage transformation during cooling. The quadruple-stage transformation was observed in the specimens aged at 773 and 798 K, and the triple-stage transformation appeared in the specimen aged at 823 K under an unregulated heat treatment atmosphere. The distribution and size of Ti 3Ni4 precipitates were heterogeneous in these specimens. The single-stage transformation in the specimen aged at 848 K was similar to that of the solution-treated specimen. In the forward quadruple-stage transformation, the R-phase transformation occurred in the intermediate region and around the grain boundary. The first martensitic transformation, which corresponded to the M1 peak in the DSC cooling curve, took place in the intermediate region of grains via the R phase. The second transformation, which corresponded to the M2 peak, occurred around the grain boundary via the R phase. The final transformation, which corresponded to the M3 peak, arose directly from the B2 parent phase at the grain centre. The transformation sequence and areas described above were quantitatively verified by comparing the SEM observations with the DSC measurements. The transformation sequence of the triple-stage transformation was also discussed..
41. Masaru Itakura, Natsuki Watanabe, Minoru Nishida, Takeshi Daio, Syo Matsumura, Atomic-Resolution X-ray Energy-Dispersive Spectroscopy Chemical Mapping of Substitutional Dy Atoms in a High-Coercivity Neodymium Magnet, Japanese Journal of Applied Physics, 10.7567/JJAP.52.050201, 52, 5 PART 1, 2013.05, We have investigated local element distributions in a Dy-doped Nd2Fe14B hot-deformed magnet by atomic-column resolution chemical mapping using an X-ray energy-dispersive spectrometer (XEDS) attached to an aberration-corrected scanning transmission electron microscope (Cscorrected STEM). The positions of the Nd and Dy atomic columns were visualized in the XEDS maps. The substitution of Dy was limited to a surface layer 2-3 unit cells thick in the Nd2Fe14B grains, and the Dy atoms preferentially occupied the 4f-Nd sites of Nd2Fe14B. These results provide further insights into the principal mechanism governing the coercivity enhancement due to Dy doping..
42. N. Watanabe, Masaru Itakura, Minoru Nishida, Microstructure of high coercivity Nd-Fe-Co-Ga-B hot-deformed magnet improved by the Dy diffusion treatment, Journal of Alloys and Compounds, 10.1016/j.jallcom.2012.12.084, 557, 1-4, 2013.04, Microstructure of Nd-Fe-Co-Ga-B hot-deformed magnet improved by the Dy diffusion treatment was investigated with high-resolution scanning electron microscopy (HRSEM), analytical transmission electron microscopy (ATEM) and high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). It was found that Dy diffuses along the thin grain boundary (GB) phase between Nd2(Fe,Co)14B grains, and then the Dy substitutes for a part of Nd near the surface of the Nd2(Fe,Co)14B grains. Consequently, two-layered-wrapping structure of thin GB phase and thin (Nd,Dy)2(Fe,Co)14B layer is formed on each Nd 2(Fe,Co)14B grain. Moreover, the Dy substitution occurs preferentially at the Nd-sites of a-planes compared with that of c-planes in the Nd2(Fe,Co)14B grains. These results indicate that the Dy diffusion treatment improves significantly the coercivity by forming the thin (Nd,Dy)2(Fe,Co)14B layer on the surface of Nd 2(Fe,Co)14B grains, although the treatment leads to grain growth and deterioration of the c-axis alignment of Nd2(Fe,Co) 14B grains..
43. M. Matsuda, Y. Iwamoto, Y. Morizono, S. Tsurekawa, K. Takashima, Minoru Nishida, Enhancement of ductility in B2-type Zr-Co-Ni alloys with deformation-induced martensite and microcrack formation, Intermetallics, 10.1016/j.intermet.2013.01.008, 36, 45-50, 2013.02, We investigated the microstructural evolution during tensile deformation of ZrCo and ternary Zr-Co-Ni alloys with the aim of clarifying the mechanism of enhancement of ductility in these alloys. Some long and slender microcracks were present perpendicular to the tensile direction on the surface of specimen with a nominal strain of 13%. There was an increase in not only the occurrence of microcracks but also the width of the microcracks with increasing nominal strain. The preferred sites for microcrack nucleation occurred at the grain boundaries and along the interface between the B2 parent phase and the Zr 2Co precipitates. Parts of the martensitic interface caused by tensile deformation acted as the preferred formation sites for the microcracks. Consequently, we consider that the remarkable enhancement of the ductility of the B2-type Zr-Co-Ni alloy is originated from the relaxation of stress concentration due to the microcrack formation, in addition to the transformation-induced plasticity associated with the deformation-induced martensite..
44. Seiichiro Ii, Mitsuhiro Matsuda, Tomomasa Matsui, Towako Fujimoto, Akinori Kakisaka, Takafumi Kikutake, Sadahiro Tsurekawa, Ken Ichi Ikeda, Minoru Nishida, Controlling grain boundary character distribution of high-temperature B2 phase in Ti-Ni-Fe alloy, Intermetallics, 10.1016/j.intermet.2012.06.009, 31, 65-71, 2012.12, A method is proposed for controlling the grain boundary character distribution of high-temperature B2 phase in Ti-Ni-Fe alloys. The method utilizes the lattice correspondence between the deformation twins in B19′ martensite and the residual planar defects in the B2 parent phase. The optimal conditions for recrystallization and additional annealing of the tensile-deformed specimen with residual strain of about 20% were determined to be 873 K for 0.9 ks and 773 K for 3.6 ks, respectively. In the specimen annealed under these optimal conditions, over 90% of grain boundaries were coincidence boundaries with ≤ 27. In particular, 33% of the grain boundaries were low-angle boundaries, that is, Σ1 boundaries. The atomic structures of the Σ9 coincidence grain boundaries and the Σ1 low-angle boundaries were observed by high-angle annular dark field scanning transmission electron microscopy. The atomic structure of these boundaries was explained well by theoretical predictions..
45. Mitsuhiro Matsuda, Yoshihiro Yasumoto, Kimiaki Hashimoto, Toru Hara, Minoru Nishida, Transmission electron microscopy of twins in 10M martensite in Ni-Mn-Ga ferromagnetic shape memory alloy, Materials Transactions, 10.2320/matertrans.M2012002, 53, 5, 902-906, 2012.10, The combination of the 10M martensite plate variants in NiMnGa ferromagnetic shape memory alloy was investigated by conventional transmission electron microscopy (CTEM) and electron diffraction experiments. There were four plate variants commonly designated as A, B, C and D, and three fundamental plate combinations can be identified in a given plate group, namely A : B (C : D) of (551) Type II, A : C (B : D) of (125) Type I and A : D (B : C) of {105} compound twins in the martensites. The boundary structure of these twins was also observed in the edge-on state by high resolution electron microscopy (HREM). The boundary of the Type I and the compound twins was not sharp in comparison to that in other shape memory alloys. There were neither ledge nor step structures at the irrational boundary in the Type II twin..
46. Minoru Nishida, E. Okunishi, T. Nishiura, H. Kawano, T. Inamura, S. Ii, T. Hara, Self-accommodation of B19 martensite in Ti-Ni shape memory alloys-Part II. Characteristic interface structures between habit plane variants, Philosophical Magazine, 10.1080/14786435.2012.669860, 92, 17, 2234-2246, 2012.06, Four characteristic interface microstructures between habit plane variants (HPVs) in the self-accommodation morphologies of B19 martensite in Ti-Ni alloys have been investigated by scanning transmission electron microscopy (STEM). The straight interface of a B 19′ type I twin is present at interface I. The relaxation of the transformation strain at interface II is achieved by a volume reduction of the minor correspondence variants (CVs) in the relevant habit plane variants (HPVs). The relaxation of the transformation strain at interface III is mainly due to the formation of a B 19′ type I twin between the two major CVs. Subsequently, local strain around the tips of the minor CVs perpendicular to the interface is released by the formation of micro-twins with the 011B 19′ type II and/or B 19′ type I relation. The major and minor CVs in each HPV are alternately connected through fine variants with the B 19′ type I twin relation parallel to interface IV. The results are compared with macroscopic observations and the predictions of PTMC analysis..
47. Minoru Nishida, T. Nishiura, H. Kawano, T. Inamura, Self-accommodation of B19′ martensite in Ti-Ni shape memory alloys-Part I. Morphological and crystallographic studies of the variant selection rule, Philosophical Magazine, 10.1080/14786435.2012.669858, 92, 17, 2215-2233, 2012.06, The self-accommodation morphologies of B19 martensite in Ti-Ni alloys have been investigated by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Twelve pairs of minimum units consisting of two habit plane variants (HPVs) with V-shaped morphology connected to a B 19′ type I variant accommodation twin were observed. Three types of self-accommodation morphologies, based on the V-shaped minimum unit, developed around one of the {111} B2 traces, which were triangular, rhombic and hexangular and consisted of three, four and six HPVs, respectively. In addition, the variant selection rule and the number of possible HPV combinations in each of these self-accommodation morphologies are discussed..
48. T. Inamura, T. Nishiura, H. Kawano, H. Hosoda, Minoru Nishida, Self-accommodation of B19′ martensite in Ti-Ni shape memory alloys. Part III. Analysis of habit plane variant clusters by the geometrically nonlinear theory, Philosophical Magazine, 10.1080/14786435.2012.669859, 92, 17, 2247-2263, 2012.06, Competition between the invariant plane (IP) condition at the habit plane, the twin orientation relation (OR) and the kinematic compatibility (KC) at the junction plane (JP) of self-accommodated B19 martensite in Ti-Ni was investigated via the geometrically nonlinear theory to understand the habit plane variant (HPV) clusters presented in Parts I and II of this work. As the IP condition cannot be satisfied simultaneously with KC, an additional rotation Q is necessary to form compatible JPs for all HPV pairs. The rotation J necessary to form the exact twin OR between the major correspondence variants (CVs) in each HPV was also examined. The observed HPV cluster was not the cluster with the smallest Q but the one satisfying Q=J with a { 1}B 19′ type I twin at JP. Both Q and J are crucial to understanding the various HPV clusters in realistic transformations. Finally, a scheme for the ideal HPV cluster composed of six HPVs is also proposed..
49. Mitsuhiro Matsuda, Kozo Yamashita, Ryutaro Sago, Kenji Akamine, Kazuki Takashima, Minoru Nishida, Development of ductile B2-Type Fe-Co based alloys, Materials Transactions, 10.2320/matertrans.M2012205, 53, 10, 1826-1828, 2012, We investigated the mechanical properties of B2-type FeCo based alloys containing minor amounts of Ni or Pd to improve their tensile ductility at room temperature. The yield and tensile stresses of the new alloys showed remarkable increases. FeCoNi alloys showed high total elongation of over 10% at room temperature. Co50Fe40Pd10 alloy displayed a tensile strength of 1250MPa and a high total elongation of 16%. The substitution of Ni or Pd into FeCo based alloys is therefore an extremely effective means of improving their room-temperature ductility..
50. Natsuki Watanabe, Masaru Itakura, Minoru Nishida, Microstructure of Nd-rich grain boundary phase in die-upset Nd-Fe-Co-Ga-B magnet, Materials Transactions, 10.2320/matertrans.M2011180, 52, 12, 2239-2244, 2011.12, Microstructure of die-upset Nd-Fe-Co-Ga-B magnet was investigated with a scanning electron microscopy (SEM), high resolution and analytical transmission electron microscopy (HRTEM and ATEM). Inside the original melt-spun flakes in the magnet, the typical texture consists of fine platelet Nd 2(Fe,Co) 14B grains surrounded continuously by a thin grain boundary (GB) phase with 2-3nm in thickness. The GB phase has an amorphous structure of which the chemical composition is Nd 44Fe 39Co 10Ga 7. It was found that high fluidity of the Nd- and Ga-rich GB phase contributes to produce a high crystallographic c-axis alignment of Nd 2(Fe,Co) 14B grains. Near the interfaces of the original flakes, morphology of the Nd 2(Fe,Co) 14B grains changes from platelet to globular involving the deterioration of c-axis alignment. Many Nd-oxide (NdO and fcc-(Nd,Fe)O x) grains and a large amount of fine Nd 3Co precipitates are formed near the interfaces, and then the composition of GB phase changes to Nd 36Fe 50Co 9Ga 5. The insufficiency of Nd in the GB phase and the existence of Nd-oxide particles prevent the anisotropic growth of Nd 2(Fe,Co) 14B grains, and then lead to the inhomogeneous GB phase and the low c-axis alignment..
51. Kazuhiro Ishikawa, Yuta Seki, Koichi Kita, Minoru Nishida, Kiyoshi Aoki, Hydrogen permeability and microstructure of rapidly quenched Nb-TiNi alloys, Journal of Alloys and Compounds, 10.1016/j.jallcom.2010.10.126, 509, SUPPL. 2, 2011.09, Effect of annealing on structure, microstructure and hydrogen permeability of rapidly quenched Nb30Ti35Ni35 and Nb 40Ti30Ni30 alloy ribbons were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and the gas flow method. Crystalline (Nb, Ti) and TiNi phases coexisted with the amorphous phases in the as-quenched Nb 30Ti35Ni35 alloy, while only crystalline (Nb, Ti) and TiNi phases were formed in the as-quenched Nb40Ti 30Ni30 alloy. Both the as-quenched alloys were too brittle to measure their hydrogen permeability, but they became ductile by annealing above 1173 K and showed the microstructure consisting of the crystalline (Nb, Ti) phase embedded in the crystalline TiNi matrix. The volume fraction of the (Nb, Ti) phases in the Nb-TiNi alloys increased with increasing Nb content. Hydrogen permeability at 673 K, i.e. Φ673 K of the crystalline Nb30Ti35Ni35 and Nb40Ti 30Ni30 alloys was 1.1 × 10-8 and 1.9 × 10-8 (molH2/m/s/Pa0.5), respectively, which were comparable with that of Pd. The present work has clearly demonstrated that the rapid quenching technique and subsequent annealing process are useful and attractive method for the preparation of hydrogen permeable Nb-TiNi alloy membrane..
52. M. Matsuda, T. Nishimoto, Y. Morizono, S. Tsurekawa, Minoru Nishida, Enhancement of ductility in B2-type Zr-Co-Pd alloys with martensitic transformation, Intermetallics, 10.1016/j.intermet.2011.02.006, 19, 7, 894-899, 2011.07, The relationship between the microstructures and the mechanical properties in the ternary Zr-Co-Pd alloys has been investigated. X-ray diffraction measurements at room temperature indicated that Zr50Co 50-xPdx alloys underwent martensitic transformation from B2 to B33 structures as a result of substituting Pd for Co at amounts greater than 12 at%. The yield and tensile strength increased at a substitution amount of 6 at%. The total elongation remarkably increased as a result of substituting Pd for Co at amounts up to 10 at%; in particular, the Zr50Co 40Pd10 alloy exhibited a considerably high total elongation of 22%. Deformation-induced martensite with a lenticular morphology was observed in the B2 parent phase near the fractured edge, in addition to dislocation with the <100>B2-type Burgers vector. Consequently, we conclude that the remarkable enhancement of the ductility is due to the transformation-induced plasticity associated with the deformation-induced martensite..
53. Mitsuhiro Matsuda, Takahiro Nishimoto, Kyohei Matsunaga, Yasuhiro Morizono, Sadahiro Tsurekawa, Minoru Nishida, Deformation structure in ductile B2-type Zr-Co-Ni alloys with martensitic transformation, Journal of Materials Science, 10.1007/s10853-010-5236-3, 46, 12, 4221-4227, 2011.06, Microstructural evolution during tensile deformation in ternary Zr-Co-Ni alloys were investigated using transmission electron microscopy to clarify the mechanism of the enhancement of ductility observed in these alloys. In Zr 50Co39Ni11 alloy deformed at room temperature, lenticular martensite is observed in the B2 parent phase immediately after yielding, in addition to dislocations with the <100>B2-type Burgers vector. The orientation relationship between the B2 parent phase and B33 martensite is determined to be [001]B2//[100]B33, (010)B2//(021)B33, and (110)B2//(010) B33. A midrib-like contrast is observed at the center of the lenticular martensite variant, and it is found to be a (021)B33 twin. A trace analysis indicates that this contrast is nearly parallel to the {100}B2, which may correspond to the habit plane of the martensite. The martensite variants grow into the B2 parent phase along the {100} B2 with increasing tensile loading, and then grid-shaped martensite variants are formed at the failure of the specimen. The martensite would be dominantly formed and grow in the regions where the stress concentration occurs during tensile deformation. It is likely that the plastic deformation mainly proceeds in the untransformed B2 parent phase because this martensite is harder than the B2 parent phase. Consequently, the authors conclude that the remarkable enhancement of ductility can be attributed to a transformation-induced plasticity associated with deformation-induced martensite..
54. Kensaku Sagara, Minoru Nishida, Hyungoo Kang, Fujio Tsumori, Hideshi Miura, Hideki Nakayama, Fabrication of super-elastic Ti-10V-2Fe-3Al alloy compacts by MIM process, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.58.361, 58, 6, 361-366, 2011.06, Titanium alloys have been used especially as aerospace, medical and dental materials because of their excellent attributes of high corrosion resistance and high specific strength. A Ti-10V-2Fe-3Al is one ofβ-titanium alloy and it shows super-elasticity. In this study, the fabrication of super-elastic Ti-10V-2Fe-3Al alloy compacts by metal injection molding which is one of near net shape forming of powders was investigated using mixed elemental and alloy powders. Under the optimized MIM process condition, nearly full density (97∼98 %) was obtained and the tensile properties of strength and elongation were 1000∼ 1050 MPa and around 5 %, respectively. Moreover, after solution treatment and aging, the compacts with alloy powder showed clearly super-elasticity..
55. Akira Chiba, Yoshihito Kawamura, Minoru Nishida, Takateru Yamamuro, Explosive welding of ZrTiCuNiBe bulk metallic glass to crystalline Cu plate, 3rd International Symposium on Explosion, Shock Wave and High-Energy Reaction Phenomena, ESHP 2010 Explosion, Shock Wave and High-Energy Reaction Phenomena, ESHP 2010, 10.4028/www.scientific.net/MSF.673.119, 119-124, 2011.05, Metallic glass or amorphous alloys have been gaining popularity due to their low density, high strength, high fracture toughness, good corrosion and good wear resistance. Especially, bulk metallic glasses (BMGs), which are made in bulk form with a thickness of ∼10mm at slow cooling rates of the order of 1∼100K/s, have been noted as an industrial application. The welding to other materials becomes very important. Explosive welding of most popular Zr41.2Ti13.8Cu10Ni12.5Be 22.5 bulk metallic glass to crystalline pure Cu plate is investigated in this paper and the BMG was found to retain the amorphous structure. The sound bonding with other materials is expected to push forward the application of BMGs for industrial usage..
56. H. Fukunaga, Y. Sugimoto, M. Nakano, T. Yanai, S. Ohta, Masaru Itakura, Minoru Nishida, Coercivity enhancement of Dy-coated Nd-Fe-B flakes by crystallization, Journal of Applied Physics, 10.1063/1.3549604, 109, 7, 2011.04, The coercivity of isotropic Dy-coated Nd-Fe-B flakes was enhanced by crystallization and simultaneous diffusion of Dy from their surfaces. Amorphous Dy-coated Nd-Fe-B flakes were crystallized by heating them to 923 K 2over a 2 min period followed by rapid cooling. During crystallization, the Dy on the surface diffused into the flakes. This low-temperature rapid annealing produced flakes with fine grains and the Dy diffusion enhanced their coercivity. The coercivity after crystallization increased with increasing Dy layer thickness, although the remanence decreased when the layer thickness exceeded 3 μm. Thick coatings of over 6 μm resulted in the formation of DyFe2, which degraded the magnetic properties of the crystallized flakes. Flakes with a 3-μm-thick coating exhibited excellent magnetic properties after annealing: They had a coercivity of 1880 kA/m and a remanence of 78 emu/g. This coercivity is approximately 500 kA/m higher than that of uncoated flakes, whereas the remanence is comparable to that of uncoated flakes..
57. S. Cao, Minoru Nishida, D. Schryvers, Quantitative three-dimensional analysis of Ni4Ti3 precipitate morphology and distribution in polycrystalline Ni-Ti, Acta Materialia, 10.1016/j.actamat.2010.11.044, 59, 4, 1780-1789, 2011.02, The three-dimensional size, morphology and distribution of Ni 4Ti3 precipitates in a Ni50.8Ti49.2 polycrystalline shape memory alloy with a heterogeneous microstructure have been investigated using a focused ion beam/scanning electron microscopy slice-and-view procedure. The mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured and/or calculated. The morphology of the precipitates was quantified by determining the equivalent ellipsoids with the same moments of inertia and classified according to the Zingg scheme. Also, the pair distribution functions describing the three-dimensional distributions were obtained from the coordinates of the precipitate mass centres. Based on this new data it is suggested that the existence of the heterogeneous microstructure could be due to a very small concentration gradient in the grains of the homogenized material and that the resulting multistage martensitic transformation originates in strain effects related to the size of the precipitates and scale differences of the available B2 matrix in between the precipitates..
58. Shanshan Cao, Minoru Nishida, Dominique Schryvers, FIB/SEM applied to quantitative 3D analysis of precipitates in Ni-Ti, Solid-Solid Phase Transformations in Inorganic Materials, 10.4028/www.scientific.net/SSP.172-174.1284, 1284-1289, 2011.01, Ni4Ti3 precipitates with a heterogeneous distribution growing in a polycrystalline Ni50.8Ti49.2 alloy have been investigated in a Dual-Beam FIB/SEM system. The volume ratio, mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured or calculated. The morphology of the precipitates was classified according to the Zingg scheme. The multistage martensitic transformation occurring in these kinds of samples is interpreted in view of the data of this heterogeneous microstructure of matrix and precipitates..
59. Kazuhiro Ishikawa, Yuta Seki, Koichi Kita, Mitsuhiro Matsuda, Minoru Nishida, Kiyoshi Aoki, Hydrogen permeation in rapidly quenched amorphous and crystallized Nb 20Ti40Ni40 alloy ribbons, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2010.10.095, 36, 2, 1784-1792, 2011.01, Formation of an amorphous (a-) Nb20Ti40Ni 40 alloy by rapid quenching and its crystallization behavior were investigated by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. The B2-TiNi phase was firstly crystallized and the remaining amorphous (a-) phase subsequently decomposed into the bcc-(Nb, Ti) + B2-TiNi phases. The crystallized (c-) Nb20Ti40Ni 40 samples obtained by annealing above 1173 K were ductile and insusceptible to hydrogen embrittlement between 598 and 673 K. Hydrogen permeability at 673 K (Φ673K) for the a- and c-Nb20Ti 40Ni40 alloys were 8.1 × 10-9 and (3.0-4.8) × 10-9 mol H2/m/s/Pa0.5, respectively. Φ673K increased with the increase in the diameter of the bcc-(Nb, Ti) phase, although this led to poor resistance to hydrogen embrittlement. The lower hydrogen permeability of the c-Nb20Ti 40Ni40 alloy was due to its lower hydrogen diffusivity. The present work demonstrated that rapid quenching and subsequent annealing are useful to prepare thermally stable Nb-TiNi hydrogen permeation alloy membranes..
60. H. Fukunaga, H. Nakayama, T. Kamikawatoko, T. Yanai, M. Nakano, F. Yamashita, S. Ohta, Masaru Itakura, Minoru Nishida, Magnetic properties of Nd-Fe-B/α-Fe multi-layered thick film magnets, Journal of Physics: Conference Series, 10.1088/1742-6596/266/1/012027, 266, 1, 2011.01, Nd-Fe-B/α-Fe multi-layered nanocomposite film-magnets were prepared from a rotating Nd
2.6
Fe
14
B/α-Fe composite target by the pulse laser deposition method with a Nd-YAG laser (λ=355 nm). The prepared film-magnets were composed of approximately 800 layers with the thickness of about several tens nanometre, and exhibited hard magnetic properties after annealing. The laser power for the ablation of the target was varied between 3 and 7 W, and it was found that the composition, magnetic properties, and the surface roughness of the prepared films depend on the laser power. A reduction in the laser power caused increases in remanence and the maximum energy product (BH)
max
as well as decreases in Nd content and coercivity of the films. All the samples had Nd-poor compositions compared with that of the Nd
2.6
Fe
14
B target and the Nd-contents of the films deposited with laser power of 3 W were less than that of the stoichiometric composition of Nd
2
Fe
14
B. The highest (BH)
max
and remanence values were obtained for a film deposited with laser power of 3 W, and were 90 kJ/m
3
and 1.0 T, respectively. The obtained high remanence value is discussed from the viewpoint of the remanence enhancement as well as the large saturation magnetization of α-Fe..
61. M. Matsuda, K. Kuramoto, Y. Morizono, S. Tsurekawa, E. Okunishi, T. Hara, Minoru Nishida, Transmission electron microscopy of antiphase boundary-like structure of B19′ martensite in Ti-Ni shape memory alloy, Acta Materialia, 10.1016/j.actamat.2010.09.017, 59, 1, 133-140, 2011.01, An antiphase boundary (APB)-like structure of the B19′ martensite in Ti-Ni alloy was investigated by transmission electron microscopy. The APB-like structure shows atomic shifts on both the (0 1 0)
B19′
plane along the c-axis and the (0 0 1)
B19′
plane along the b-axis; a kind of ledge-and-step structure on the b-c plane, in addition to a displacement along the a-axis. The displacement vector can be expressed as R = 〈-0.1648 1/2 0.4328〉 in terms of the conventional atomic coordinates of Ti and Ni in the B19′ martensite. The APB-like structure is not inherited from APB in the B2 parent phase. We conclude that the APB-like structure is developed by accidental impingement of differently nucleated martensitic domains during the transformation. This structure is defined as a kind of stacking fault with an APB-like contrast..
62. Mitsuhiro Matsuda, Shoichiro Yano, Minoru Nishida, Morphology and crystallography of martensite plate with long period stacking structure in Ti-Pd shape memory alloy, Materials Transactions, 10.2320/matertrans.M2011187, 52, 11, 2016-2021, 2011, The morphology and crystallography of martensite plates with a long period stacking structure in Ti-Pd shape memory alloy were investigated by transmission electron microscopy. In addition to B19 (2H) martensite, an 18R(21)6 structure was observed in equiatomic Ti-Pd alloy quenched above 1373 K. Three fundamental plate variant combinations were identified in the plate group in the region consisting exclusively of 18R martensite. These were designated A : B, A : C and A : Dtypes, and their morphologies and crystallographic characteristics are a wedge with type II, a spear with type I and a fork with compound twin relations, respectively. Duplex martensitic phases coexisting in the same area, namely, "two-in-one" structures, were also observed..
63. Masahiro Ishimaru, Masaru Itakura, Minoru Nishida, Masaki Nakano, Hirotoshi Fukunaga, Microstructure analysis of high coercivity PLD-Made Nd-Fe-B thick-film improved by Tb-coating-diffusion treatment, Materials Transactions, 10.2320/matertrans.M2010189, 51, 10, 1939-1943, 2010.10, Microstructure of high coercive pulsed laser deposition (PLD) made Nd-Fe-B thick-film magnet improved by "Tb-coating-diffusion" treatment has been investigated with an analytical transmission electron microscope (ATEM). It was found that the PLD-made film consists mainly of fine Nd2Fe 14B grains about 200 nm in diameter and a large amount of Nd intergranular phases. Energy dispersive X-ray spectroscopy (EDS) analysis showed that each Nd2Fe14B grain is covered with a thin (Nd,Tb)2Fei4B layer about 20-30 nm in thickness and thin Nd-Tb grainboundary-layer about 5-10 nm in width. The present results indicate that such a two-layered-wrapping structure enhances significantly the coercivity of the PLD-made thick-film magnet..
64. H. Miura, N. Nishiyama, N. Togashi, Minoru Nishida, A. Inoue, Structure, conductivity and mechanical properties of non-equilibrium copper-based crystalline alloy nano-composites, Intermetallics, 10.1016/j.intermet.2010.02.033, 18, 10, 1860-1863, 2010.10, Beryllium copper (Cu-Be) alloys exhibit well-balanced properties of strength, elongation and conductivity, and have been used as the conventional material of electrical contacting parts. However, improved materials with higher performances are strongly required for miniaturization of their parts and environmental issues of Be. Recently, an alloy design on the basis of glass-forming rules has enabled the development of Cu-Zr-Ag alloys with tensile strength of 1200 MPa, plastic elongation of 3.1% and electrical conductivity of 30.7% IACS in a thin strip form through the simple production process of casting, cold rolling and annealing. This paper intends to present microstructure and properties of the newly developed alloys and discuss the possibility for applying to electrical contacting materials..
65. Yasuhiro Morizono, Seiichiro Nakatsukasa, Minoru Nishida, Bonding and separation behaviors between Ti-Sn alloys and high carbon steel, 6th International Conference on Processing and Manufacturing of Advanced Materials - THERMEC'2009 THERMEC 2009, 10.4028/www.scientific.net/MSF.638-642.3787, 3787-3792, 2010.02, Ti-Sn binary alloys (Ti-5 to 20 mol% Sn) were diffusion-bonded to high carbon steel between 1073 and 1273 K for 3.6 ks in a vacuum to investigate the influence of the alloy composition on the interfacial microstructures. Ti-5 and 10 mol% Sn alloys were attached firmly to the steel at a bonding temperature of 1273 K. A continuous TiC layer was formed along the interface, while voids were observed between the TiC layer and the steel. Although the joints with Ti-15 and 20 mol% Sn alloys were also prepared at 1273 K, these joints separated near the interface after the bonding treatment. The TiC layer was formed in the separated surface of Ti-Sn alloy, and Fe in the steel diffused into the Ti-Sn alloy. This indicates that the Ti-15 and 20 mol% Sn alloys established contact with the steel at elevated temperatures until just before the separation. The specimens bonded at 1173 K also denoted the same tendency. However, the Ti-15 mol% Sn/steel joint bonded at 1073 K showed a shear strength of more than 50 MPa. The mechanism and the application of the interface separation are discussed on the basis of the microstructural observations..
66. Mitsuhiro Matsuda, Katsutoshi Hayashi, Minoru Nishida, Microstructure and mechanical properties of Zr-Co-Ni intermetallic compound, 6th International Conference on Processing and Manufacturing of Advanced Materials - THERMEC'2009 THERMEC 2009, 10.4028/www.scientific.net/MSF.638-642.1379, 1379-1383, 2010.02, The relationship between the microstructure and mechanical properties on the ternary ZrCoNi alloys has been investigated. Zr50Co 50-xNix alloys undergo martensitic transformation from the B2 to B33 structure by the substitution of Ni for Co. The tensile ductility at room temperature increases remarkably without the loss of yield strength by substituting Ni. Zr50Co39Ni11 alloy has the extremely high plastic elongation of 21%. There are many {021}B33 deformation twins in the B2 parent phase just near the tensile fractured area. These twins are the strain induced martensitic phase due to the tensile deformation. Consequently, the remarkable improvement of the ductility of ZrCoNi alloys is due to the transformation induced plasticity..
67. Tetsuya Kusuno, Yusuke Shimada, Mitsuhiro Matsuda, Masaaki Otsu, Kazuki Takashima, Minoru Nishida, Kazuhiro Ishikawa, Kiyoshi Aoki, Micromechanical testing of nanostructured NbTiNi hydrogen permeation membranes, 2009 MRS Fall Meeting Mechanical Behavior at Small Scales - Experiments and Modeling, 1224, 45-50, 2010, Nb-Ti-Ni alloy is one of the candidates for hydrogen permeation membranes. The hydrogen permeability of a membrane depends on its thickness, and mechanical properties such as the fracture toughness of the membrane are important to ensure reliability and durability. In the present work, micro-mechanical tests have been carried out for melt-spun Nb-Ti-Ni thin films consisting of amorphous and nano-crystalline phases. The relationship between the mechanical properties of the melt-spun films and the microstructural changes occurring in the films due to heat treatment has been also discussed. The Nb-Ti-Ni alloy thin films were prepared by the melt-spun technique and then heat-treated at 873-1173 K. Micro-sized cantilever specimens with dimensions of 10 × 10 × 50 μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out using a mechanical testing machine for the micro-sized specimens; the testing machine was developed by us. In addition, microstructures were observed by transmission electron microscopy (TEM). The fracture toughness (KQ) value decreased up to 823 K, and it increased above 1173 K. The specimen heat-treated above 1173 K showed ductile fracture. The fracture morphology of the specimen heat-treated up to 1023 K showed grain boundary fracture characteristics, and that of the specimen heat-treated at 1173 K changed to transgranular fracture..
68. T. Hara, Y. Yamabe-Mitarai, Minoru Nishida, E. Okunishi, Analysis of stacking structure and morphology in Ti50(Pt x,Ir50-x) martensite by HRTEM and HAADF-STEM, 12th International Conference on Martensitic Transformations, ICOMAT-08 Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08, 659-662, 2009.12, The stacking order and morphology of Ti50(Ptx,Ir50-x) martensite were investigated to elucidate the compositional dependence of mechanical properties. Microstructure and stacking sequence were analyzed by TEM, SAED, HRTEM and HAADF-STEM. Observations by (S)TEM revealed each alloy to show different stacking orders: 4H, 6H and 7R for Ti50Pt 12.5lr37.5, Ti50Pt37.5Ir 12.5 and Ti50Pt25Ir25 alloy, respectively. The twinning microstructure also varied according to alloy composition. Ti50Pt12.5lr37.5 alloy is covered with two types of twin, while there are very few twins in Ti50Pt 37.5lr12.5 alloy..
69. M. Matsuda', M. Yamashita, Kyosuke Hirayama, T. Hara, Minoru Nishida, Transmission electron microscopy of antiphase boundary-like structure y induced by displacive transformation in Ti-Pd shape memory alloy, 12th International Conference on Martensitic Transformations, ICOMAT-08 Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08, 305-309, 2009.12, An antiphase boundary (APB)-like structure in the B19 martensite of Ti-Pd alloy has been investigated by transmission electron microscopy. High-resolution and high-angle annular dark-field scanning transmission electron microscopy images demonstrate the presence of an APB-like contrast along the (001) basal plane of the B19 martensite. The contrast is not inherited from the APB with a displacement vector of the type R = (1/2)<111> in the B2 parent phase. In-situ heating observations indicate that the APBlike contrast disappears above A
f
temperature. These facts suggest that the boundary is induced by the local heterogeneity of atomic movements during the martensitic transformation. Therefore, we have newly proposed that the APB-like structure in the B19 martensite is defined as the displacive transformation-induced APB..
70. N. Watanabe, H. Umemoto, M. Ishimaru, Masaru Itakura, Minoru Nishida, K. MacHida, Microstructure analysis of Nd-Fe-B sintered magnets improved by Tb-metal vapour sorption, Journal of Microscopy, 10.1111/j.1365-2818.2009.03231.x, 236, 2, 104-108, 2009.11, Behaviours of constituent elements in the Nd-Fe-B sintered magnets improved by Tb-metal vapour sorption have been investigated by using an analytical transmission microscopy. It was found that a triple junction of the grain boundaries consists of fine Nd-O crystalline and amorphous phase. The energy dispersive X-ray spectroscopy (EDS) analysis showed that the amorphous phase mainly consists of Co, Nd and Tb. The Tb-treatment causes the formation of the amorphous Co-Nd(Tb) wetting-layer phase which wraps each Nd2Fe 14B grain. The results suggest that the wrapped structure prevents the nucleation of magnetic reversed domains and then improves significantly the coercivity of the magnet..
71. Mitsuhiro Matsuda, Yusuke Shimada, Takuya Murasaki, Minoru Nishida, Kazuhiro Ishikawa, Kiyoshi Aoki, Crystallization and microstructure changes in rapidly solidified Nb20Ti40Ni40 hydrogen permeation alloy, Journal of Alloys and Compounds, 10.1016/j.jallcom.2009.06.094, 485, 1-2, 773-777, 2009.10, The crystallization behaviors and microstructure changes by heat treatments in the rapidly solidified Nb20Ti40Ni40 hydrogen permeation alloy have been investigated. There are two exothermic peaks at 872 and 914 K in DSC heating curve. The first and second peaks correspond to the crystallization of B2-TiNi and bcc-Nb phases, respectively. The orientation relationship of these two phases is cube-on-cube relation. The specimens annealed from 773 to 923 K are quite brittle, although those microstructures consist of fine equiaxed grains less than 50 nm. With prolonged annealing above 948 K the grain size is increased to about 150 nm or more and the hardness is decreased around 250 Hv, thus the ductility is recovered. These results suggest that the high temperature annealing is required for the application of the melt-spun ribbon to the hydrogen permeation membrane..
72. Mitsuhiro Matsuda, Katsutoshi Hayashi, Minoru Nishida, Ductility enhancement in B2-Type Zr-Co-Ni alloys with martensitic transformation, Materials Transactions, 10.2320/matertrans.M2009182, 50, 9, 2335-2340, 2009.09, The relationship between the microstructures and mechanical properties in the ternary Zr-Co-Ni alloys has been investigated. X-ray diffraction measurements at room temperature show that Zr50Co50Ni alloys undergo martensitic transformation from the B2 to B33 structures by the substitution amounts of Ni above 14% for Co. The tensile strength and elongation increase remarkably by substituting Ni up to 13%. Especially, the Zr 50oCo39Ni11 alloy has the extremely high total elongation of 23%. There are many (021 )b33 deformation twins in addition to the dislocations with the (lOO)-type Burgers vector just near the fractured area. These twins are considered to be an internal defect of the deformation induced martensite which has high hardness about 430 Hv. Therefore, it is concluded that the remarkable enhancement of the ductility of Zr-Co-Ni alloys is due to the transformation induced plasticity..
73. Yasuhiro Morizono, Yoshikazu Kodama, Takateru Yamamuro, Minoru Nishida, Influence of heating temperature on interface separation behavior between Ti-20 mol% Al alloy and high carbon steel, Materials Transactions, 10.2320/matertrans.M2009035, 50, 8, 2005-2010, 2009.08, Ti-20 mol% Al (Ti-12.3 mass% Al) alloy was diffusion-bonded to high carbon steel (0.82 mass% C) at 1273 K for 3.6 ks in a vacuum. The joint had a space of a few micrometers in thickness between the Ti-20 mol% Al alloy and the steel, and several specimens separated near the interface promptly after the bonding treatment. This phenomenon is referred to as 'interface separation'. This paper describes the influence of heating temperature on the interface separation. Diffusion bonding of the Ti-20 mol% Al alloy to the high carbon steel was carried out at 1173 to 1423 K for 0.9 to 3.6 ks in a vacuum, and then several joints were heated at a given temperature for up to 176.4 ks in an evacuated silica tube. At 1173 K, the separation phenomenon could not be confirmed even after prolonged heat treatment. This joint had four kinds of reaction regions in the vicinity of the interface, and their thicknesses increased in proportion to square root of holding time. On the other hand, the joint bonded at more than 1273 K showed the separation at the interface. As the heating temperature increased, the holding time required to induce the phenomenon became shorter. To clarify a time when the separation occurs in the diffusion bonding process, the joint with a special shape was prepared and quenched into the water from 1273 K. The generation of voids was recognized at the interface. These results suggest that the occurrence of the interface separation is associated with interdiffusion between the Ti-20 mol% Al alloy and the steel..
74. Tomohiro Nishiura, Minoru Nishida, Internal defects of B19' martensite via R-phase in Ti-Ni-Fe and thermally cycled Ti-Ni alloys, Materials Transactions, 10.2320/matertrans.MER2008430, 50, 5, 1219-1224, 2009.05, Crystallography and morphology of B19' martensite via R phase transformation in Ti-Ni-Fe alloy have been investigated by X-ray diffraction and transmission electron microscopy. The microstructure aspects of the B19' martensite in the solution treated Ti-Ni-Fe alloy was the same as those in the solution treated binary Ti-Ni alloy. In the thermal cycled Ti-Ni-Fe alloy, the (001)b19' compound twins frequently observed were the same as those in the thermal cycled binary Ti-Ni alloy. It is considered that the (001) b19' compound twin was a kind of deformation twin to reduce the internal stress due to dislocations introduced during the thermal cycle, rather than a lattice invariant shear of the R to B19' transformation..
75. H. M. Ghasemi, M. Emamy, H. Eskandari, K. Hokamoto, Minoru Nishida, M. Matsuda, Interfacial characterisation in Al-20 vol.-%SiCp explosively compacted composite, Materials Science and Technology, 10.1179/174328408X332799, 25, 1, 108-110, 2009.01, Al-20 vol.-%SiCp composite was prepared using direct explosive compaction. Interfacial characterisation of the composite was preformed using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that the interface seemed to be clean and no interfacial AI4C3 reaction product was generated along the interface between SiC particles and Al matrix. The results also showed a better bonding between SiC particles and Al matrix in the central region of the compact sample..
76. Minoru Nishida, M. Matsuda, Y. Shimada, K. Takashima, K. Ishikawa, K. Aoki, Microstructural and mechanical characterizations of rapidly solidified Nb-TiNi hydrogen permeation alloy, Journal of Physics: Conference Series, 10.1088/1742-6596/144/1/012106, 144, 2009.01, The microstructural and mechanical characterizations of the rapidly solidified Nb20Ti40Ni40 (at%) hydrogen permeation alloy have been performed. An as-melt spun ribbon consists of an amorphous phase with sound bending ductility. The successive crystallization of B2-TiNi and bcc-Nb solid solution phases takes place during heating. The amorphous phase is stable in the specimens annealed below 773 K. The specimens annealed from 798 to 923 K are quite brittle, although those consist of fine equiaxed grains less than 50 nm. With annealing above 948 K for prolonged periods the grain size is increased to about 150 nm or more and the hardness is decreased about 260 Hv or less. Consequently, the ductility is recovered. The fracture toughness of as-melt spun and annealed ribbons is also investigated by the micromechanical test..
77. Yasuhiro Morizono, Yusuke Hirokawa, Minoru Nishida, Effect of aging treatment on explosive welding process of beryllium copper to steel, Science and Technology of Energetic Materials, 70, 1-2, 43-48, 2009, Beryllium copper (Cu-Be alloy) was bonded to austenitic stainless steel by explosive welding. The effect of aging treatment for the Cu-Be alloy on the interfacial microstructures and the mechanical properties of the joints was investigated. Before bonding, the Cu-Be alloy was solution-treated at 1073 K for 1.8 ks (1800 s) and then aged at 588 K for 3.6 and 10.8 ks. A wavy interface was formed in the joints with the non-aged and aged Cu-Be alloys. These joints differed markedly in the wavelength and the amplitude of the interface due to precipitation hardening of the Cu-Be alloy. However, fine grains of about 50 nm in diameter were observed along the collision interface in these joints. The formation of the fine grains is considered to be the trace of melting and subsequently rapid solidification at the contact surface of the Cu-Be alloy. The high hardness of the aged Cu-Be alloy was retained even after explosive welding, and the joint with the Cu-Be alloy aged at 588 K for 10.8 ks showed a bonding strength of about 700 MPa. On the other hand, the joint with the non-aged Cu-Be alloy was aged at 588 K for 10.8 ks after welding, and its bonding strength reached about 700 MPa. This indicates that explosive welding, which is characterized by extremely narrow heat-affected zone, is suited to the bonding method for the precipitation hardening Cu-Be alloy. The explosively welded Cu-Be alloy/carbon steel joint was also prepared, and the same tendency was recognized..
78. Yasuhiro Morizono, Yoshikazu Kodama, Takateru Yamamuro, Minoru Nishida, Interface separation phenomenon in Ti-20mol%Al alloy/iron material joints, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.94.251, 94, 7, 251-257, 2008.12, Ti-20mol%Al (Ti-20Al, i.e. Ti-12.3mass%Al) alloy was diffusion-bonded to eutectoid steel at 1273 K for 3.6ks in a vacuum. The joint had a space of a few micrometers in thickness between the Ti-20Al alloy and the steel, and several specimens separated near the interface promptly after the bonding treatment. This phenomenon, which is referred to as "interface separation", is known to depend on alloy composition, bonding temperature and holding time. This paper describes the influence of carbon content in iron materials on the interface separation. Four kinds of carbon steels, an alloy steel and a cast iron were used as a mating material for the Ti-20Al alloy. Diffusion bonding was carried out at 1273K for 3.6 ks in a vacuum. The diffusion of constituent elements into each parent material and the formation of reaction phases were observed in the vicinity of the interface in all cases. The interface separation was clearly seen in the joints with the carbon steels and the cast iron containing more than 0.82 mass% C. It was also confirmed that the space formed near the interface spread to the iron material side. On the other hand, the bonding of the Ti-20Al alloy to the alloy steel with high carbon content was achieved without incident. In this joint, the diffusion of Fe into the Ti-20Al side was inhibited by TiC layer formed at the interface. The mechanism of the interface separation is discussed from the viewpoint of thermal stress, reaction phase and diffusion behavior..
79. Yusuke Shimada, Mitsuhiro Matsuda, Yuji Kawakami, Masaaki Otsu, Kazuki Takashima, Minoru Nishida, Kazuhiro Ishikawa, Kiyoshi Aoki, Micromechanical characterization of rapidly-solidified Nb-TiNi hydrogen permeation alloy membranes, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.72.1015, 72, 12, 1015-1020, 2008.12, The micromechanical tests have been performed for melt-spun Nb-TiNi ribbons, and the relation between the mechanical properties and microstructural change with heat treatment has been investigated. Micro-cantilever specimens with dimensions of 10(B) × 20(W) × 50(L) μm 3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out at room temperature in air using a mechanical testing machine developed for micro-sized specimens. The fracture toughness value (K Q) of as-melt spun ribbon which consists of an amorphous phase was 5.3 MPam 1/2. In contrast, the K Q of the melt-spun ribbon annealed at 773 K for 3.6 ks decreases to 2.8 MPam 1/2. With annealing above 973 K fracture toughness increases again. This is due to the nanocrystallization of the amorphous phase and the formation of aggregates which are composed of B2-TiNi and bcc-Nb (Ti) phase with the cube-on-cube orientation relationship. These results suggest that the high temperature annealing is required for the application to the hydrogen permeation membrane..
80. Minoru Nishida, M. Matsuda, Y. Yasumoto, S. Yano, Y. Yamabe-Mitarai, T. Hara, Crystallography and morphology of twins in equiatomic TiPt martensite, Materials Science and Technology, 10.1179/174328408X302549, 24, 8, 884-889, 2008.10, Twins in the B19 (2H) martensite in Ti-Pt shape memory alloy have been investigated by transmission electron microscopy. There are three twinning modes evident, i.e. {111}2H Type I, 〈121〉2H Type II and {101}2H compound twins. In addition to the 2H martensite, various long period stacking structures are observed such as 21̄12̄ stacking and incommensurate like modulated martensites. It Is frequently observed that two martensite structures derived from the identical closed packed plane of the parent phase coexist in the same area, namely, 'two-in-one' morphology. The crystallographic aspects of the 'two-in-one' morphology are also discussed..
81. Mitsuhiro Matsuda, Takuya Murasaki, Minoru Nishida, Kazuhiro Ishikawa, Kiyoshi Aoki, Electron microscopy study of eutectic structure in Nb-Ti-X and Nb-Zr-X (X = Co, Ni) hydrogen permeation alloys, Materials Transactions, 10.2320/matertrans.MA200803, 49, 10, 2208-2213, 2008.10, The morphology and crystallography of eutectic structures in several niobium-bearing hydrogen permeation alloys such as Nb20Ti 40Ni40. Nb30Ti35Co35. Nb13Zr43Ni44, and Nb25Zr 35Co40 have been investigated by means of transmission electron microscopy. The alloys Nb20Ti40Ni40, Nb30Ti35Co35, and Nb25Zr 35Co40 possess eutectic structures consisting of fine lamellar morphology with Nb-based bcc and B2 intermetallic phases. The Nb 13Zr43Ni44 alloy possesses a eutectic structure consisting of rod-shaped bcc-(Nb, Zr) phase and B33-ZrNi phase which displacively transforms from the B2 high-temperature phase. The eutectic structures in the Nb20Ti40Ni40 and the Nb 25Zr35Co40 alloys exhibit a cube-on-cube orientation relationship between the bcc and B2 phases. The eutectic structure in the Nb13Zr43Ni44 alloy also exhibits a cube-on-cube orientation relationship by considering the lattice correspondence between the B2 and the B33 structures. On the other hand, a unique orientation relationship is found out in the Nb30Ti35Co35 alloy, as follows: (110)(Nb, Ti) // (110)TiCo, [2̄21](Nb, Ti) // [001]TiCo. The atomic arrangements at the eutectic interface are also discussed on the basis of high-resolution observations..
82. Minoru Nishida, T. Hara, M. Matsuda, S. Ii, Crystallography and morphology of various interfaces in Ti-Ni, Ti-Pd and Ni-Mn-Ga shape memory alloys, Materials Science and Engineering A, 10.1016/j.msea.2007.01.179, 481-482, 1-2 C, 18-27, 2008.05, Crystallography and morphology of various interfaces in Ti-Ni, Ti-Pd and Ni-Mn-Ga shape memory alloys are investigated by transmission electron microscopy. Neither ledge nor step structures are recognized at the irrational interface of the <0 1 1>
B19′
type II twin in Ti-Ni martensite and the <1 2 1>
B19
type II twin in Ti-Pd martensite in the two dimensional lattice image from the η
1
direction. The combination of plate variants of the 10 and the 14 M Ni-Mn-Ga martensites is subsequently discussed. There are four plate variants commonly designated as A, B, C and D, and three fundamental plate combinations can be identified in a given plate group, namely A: B (C: D) of type II, A: C (B: D) of type I and A: D (B: C) of compound twins in both the martensites. An interesting phenomenon is the migration of A: D boundary in the 10 M martensite during the observation. Finally, we present the atomic structures of {1 1 4}
B2
Σ9 boundary in the B2 parent phase of Ti-Ni. The influence of heat treatment atmosphere on the boundary structures is also discussed..
83. T. Nishiura, K. Hayashi, Minoru Nishida, Electropolishing conditions for trace analysis of B19′ martensite in Ti-Ni shape memory alloys, Materials Science and Engineering A, 10.1016/j.msea.2007.01.181, 481-482, 1-2 C, 446-451, 2008.05, The electropolishing conditions of thin foil specimens for the crystallographic analysis of the B19′ martensite in the Ti-Ni shape memory alloy have been investigated. The specimens are electropolished between the martensite-start and the martensite-finish temperatures in three electrolytes; H2SO4-CH3OH, HNO3-CH3OH and HClO4-(CH3CO)2O. The traces of the martensite morphology are clearly retained on the foil surface polished in the HNO3-CH3OH solution. The microreversibility of the martensite morphology during in situ cooling experiments in the transmission election microscope is examined in the obtained foil. No microreversibility is observed in the foil. In order to confirm the validity of the residual traces for the crystallographic investigation of the martensite morphology, a preliminary analysis based on the lattice correspondence between the B2 and B19′ structures is carried out..
84. Mitsuhiro Matsuda, Toru Hara, Minoru Nishida, Crystallography and morphology of antiphase boundary-like structure induced by martensitic transformation in Ti-Pd shape memory alloy, Materials Transactions, 10.2320/matertrans.MBW200715, 49, 3, 461-465, 2008.03, An antiphase boundary (APB)-like structure in the B19 martensite of Ti-Pd alloy has been investigated by transmission electron microscopy. High-resolution and high-angle annular dark-field scanning transmission electron microscopy images demonstrate the presence of an APB-like contrast along the (001) basal plane of the B19 martensite. The contrast is not inherited from the APB with a displacement vector of the type R = (1/2)(111) in the B2 parent phase. These facts suggest that the boundary is induced by the local heterogeneity of atomic movements during the martensitic transformation. Therefore, we have newly proposed that the APB-like structure in the B19 martensite is defined as the displacive transformation-induced APB..
85. Sh Khameneh Asl, M. Heydarzadeh Sohi, K. Hokamoto, M. Matsuda, R. Tomoshige, Minoru Nishida, Study of phase transformations in heat treatment of HVOF thermally sprayed WC-17Co coating, 2nd International Symposium on Explosion, Shock Wave and Hypervelocity Phenomena, ESHP-2 Materials Science Forum, 566, 161-166, 2008.01, In this work, WC-17Co powder was thermally sprayed onto mild steel using HVOF spray technique. The coated specimen was heat treated at 1100°C in a vacuum chamber and was then studied by using transmission electron microscopy (TEM). Post heat treatment resulted in recrystallization of the amorphous phase, formed during thermal spraying, into low carbon eta phase like Co 6W6C TEM results of the heat treated specimens showed that these new nucleated eta phases had very clear crystallographic structure without any crystalline defects. Heat treatment could also transform high carbon carbides like WC and W2C in the as sprayed samples to high carbon eta phases like Co3W3C. High density of dislocations and staking faults noticed in TEM of these phases might be an indication of possible shear mechanism in formation of these carbides..
86. A. Chiba, Y. Kawamura, Minoru Nishida, Explosive welding of ZrTiCuNiBe bulk metallic glass to crystalline metallic plates, Materials Science Forum, 566, 119-124, 2008, Recently, a number of amorphous alloys that possess high glass-forming ability and a wide supercooled liquid region before crystallization have been discovered. Especially, bulk metallic glasses, which are made in bulk form with a thickness of ∼10 mm at slow cooling rates of the order of 1-100 K/s, have been noted as an industrial application. Hence the welding of bulk metallic glasses to other materials is very important. Explosive welding of most popular Zr41.2Ti13.8Cu10Ni12.5Be 22.5 bulk metallic glass to crystalline pure Ti and SUS304 plates is investigated in this paper. The BMGs was found to retain the amorphous structure and the original mechanical properties. The sound bonding with other materials is expected to push forward the application of bulk metallic glass for industrial usage..
87. Emil Omurzak, Janar Jasnakunov, Nazgul Mairykova, Alima Abdykerimova, Aigul Maatkasymova, Saadat Sulaimankulova, Mitsuhiro Matsuda, Minoru Nishida, Hirotaka Ihara, Tsutomu Mashimo, Synthesis method of nanomaterials by pulsed plasma in liquid, Journal of Nanoscience and Nanotechnology, 10.1166/jnn.2007.804, 7, 9, 3157-3159, 2007.09, A new synthesis method of nanomaterials using pulsed plasma in liquid by the low voltage spark discharge is presented. The fullerene C 60 and TiO nanopowder were for the first time synthesized by electric discharge method in liquid. The purity of C 60 was >99%, which is much higher than those by the conventional arc plasma in inert gas methods (less than 80% C 60 and 20% C 70 and other fullerenes). Copper nanoparticles prepared by this method were smaller than those by arc method by a factor of >5. The pulsed plasma in liquid enables us to quench from plasma state, by which we can synthesize nanomaterials, metastable materials, etc. In addition, the applied power is 100 times smaller than those of arc discharge..
88. Yasuhiro Morizono, Takateru Yamamuro, Minoru Nishida, Interfacial reaction between Ti-Al binary alloys and high carbon steel, Materials Transactions, 10.2320/matertrans.MRA2007012, 48, 6, 1476-1482, 2007.06, Diffusion bonding of Ti-Al binary alloys (Ti-10 to 40 mol% Al) to high carbon steel was carried out between 1073 and 1273 K for 0.9 to 8.1 ks in a vacuum, and the effect of the alloy composition on the interfacial microstructures and the bonding strength was investigated. Three regions, which were composed of reaction products with Ti, Al and Fe, a TiC layer, and ferrite, were formed around the interface, regardless of the alloy composition. The thickness of each region changed with an increase in the Al content in the Ti-Al alloy. In general, the TiC layer formed in Ti/steel joints is known to act as a barrier for diffusion of constituent elements across the interface and to inhibit the formation of other reaction products. In this study, the barrier effect of the TiC layer was overcome by the existence of Al. Although the Ti-Al/steel joints showed a relatively high bonding strength of more than 150MPa in many cases, the joint with Ti-20mol% Al alloy separated near the interface promptly after bonding treatment at 1273 K for 3.6 and 8.1 ks. The details and the application of the separation phenomenon are discussed..
89. K. Hamasuna, C. Iwamoto, S. Satonaka, Minoru Nishida, R. Tomoshige, M. Fujita, Development of resistance welding for silicon carbide, Materials Transactions, 10.2320/matertrans.48.1060, 48, 5, 1060-1063, 2007.05, Resistance welding was applied to the bonding of SiC to metals. The welded interface structure was observed by high-resolution transmission electron microscopy to reveal the reaction during welding. The maximum bonding temperature of SiC varied with the rate of welding current rise. At the welded interface, Al4C3, Al and an amorphous phase were formed adjacent to SiC in the SiC/Al system. The SiC/Al interface was flat at the atomic level and the crystallographic orientation relationship between SiC and Al was observed. For the SiC/Ag-Cu-Ti alloy system, the reaction phases TiC and Ti5Si3 were formed at the interface. The thickness of the reaction phases varied with the rate of welding current rise, and, under specific welding conditions, Ag formed directly adjacent to SiC without the reaction phases..
90. M. Matsuda, T. Hara, E. Okunishi, Minoru Nishida, High-angle annular dark field scanning transmission electron microscopy of the antiphase boundary in a rapidly solidified B2 type TiPd compound, Philosophical Magazine Letters, 10.1080/09500830601105667, 87, 1, 59-64, 2007.01, High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast is applied to characterize the antiphase boundary (APB) of the B2 structure in a rapidly solidified TiPd melt-spun compound. The atomic shift associated with the R=(1/2)a0 〈111〉 type displacement vector is directly observed at the boundary. A microstructure modification of the melt-spun compound with the cooling rate during solidification is also described..
91. Yasuhiro Morizono, Minoru Nishida, Yoshikazu Kodama, Takateru Yamamuro, Yasuhide Ohno, Surface modification technique using interfacial reaction between Ti-Al alloy and steel, 5th International Conference on Processing and Manufacturing of Advanced Materials - THERMEC'2006 Supplement to THERMEC 2006, 5th International Conference on PROCESSING and MANUFACTURING OF ADVANCED MATERIALS, THERMEC 2006, 539-543, 1248-1252, 2007, Diffusion bonding of Ti and Ti-Al (Ti-10, 20 and 40 mol%Al) alloys to high carbon steel was carried out at 1073 and 1273 K for 3.6 ks in a vacuum. It has been found that the joint with Ti-20 mol%Al alloy is separated in the vicinity of the interface promptly after the bonding treatment at 1273 K. Such a phenomenon could not be observed in other Ti-Al alloy/steel joints, and the Ti-20 mol%Al alloy/steel joint bonded at 1073 K showed a high strength of about 170 MPa. Therefore, this phenomenon depends on the bonding temperature and the composition of the Ti-Al alloys. From the observation results of the interface, it is thought that the diffusion of constituent elements across the interface is part of the reason for the separation phenomenon. The separated surface of the Ti-20 mol%Al alloy side showed diffraction peaks of TiC phase by XRD. Its Vickers hardness was about 1200 and approximately 4 times higher than that before the bonding treatment. It is expected that the separation phenomenon at the Ti-20 mol%Al alloy/steel interface serves surface modification of titanium materials, which show poor wear resistance..
92. Minoru Nishida, M. Matsuda, T. Fujimoto, K. Tanka, A. Kakisaka, Hideharu Nakashima, Crystallography of deformation twin boundaries in a B2 type Ti-Ni alloy, Materials Science and Engineering A, 10.1016/j.msea.2006.03.111, 438-440, SPEC. ISS., 495-499, 2006.11, The deformation structure of B2 parent phase in Ti-Ni shape memory alloy around 573 K has been investigated by transmission electron microscopy. Serrations are seen in stress-strain curve, which corresponds to the formation of various planar defects of twin relation with respect to {1 1 2} {1 1 3}, {1 1 5}, {4 4 7} planes and so on. These defects can be expressed by particular Σ values on the basis of the coincidence site lattice model, since they are 〈1 1 0〉 symmetric tilt boundaries in a wide sense. It is also demonstrated that the sigma combination rule of the coincidence site lattice model can be applied to the triple junction of such defects..
93. T. Maeshima, S. Ushimaru, K. Yamauchi, Minoru Nishida, Effect of heat treatment on shape memory effect and superelasticity in Ti-Mo-Sn alloys, Materials Science and Engineering A, 10.1016/j.msea.2006.05.092, 438-440, SPEC. ISS., 844-847, 2006.11, Ti-Mo-Sn alloys have been developed as a substitute for Ti-Ni alloys in the biomedical field. The effect of heat treatment on shape memory and superelastic properties in Ti-Mo-Sn alloys has been investigated. The shape memory effect is improved by aging at 873 K for 180-420 s in the Ti-5 mol% Mo-4 mol% Sn alloy and superelasticity is improved by aging at 873 K for 180-300 s in the Ti-5 mol% Mo-5 mol% Sn alloy. A large superelasticity with the recovery strain of 3.5% is obtained in the Ti-5 mol% Mo-5 mol% Sn alloy aged at 873 K for 300 s at room temperature. It has been understood that the improvement of superelasticity is due to an increment in the recovery strain with the reverse transformation of stress induced martensite. The superelasticity in Ti-5 mol% Mo-5 mol% Sn alloy aged at 873 K for 300 s is superior to that in the solution-treated alloy over wide temperature range..
94. K. Fujishima, Minoru Nishida, Y. Morizono, K. Yamaguchi, K. Ishiuchi, T. Yamamuro, Effect of heat treatment atmosphere on the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys, Materials Science and Engineering A, 10.1016/j.msea.2006.05.048, 438-440, SPEC. ISS., 489-494, 2006.11, We demonstrated by systematic experiments that the appearance and disappearance of a multistage martensitic transformation in aged Ni-rich Ti-Ni alloys depends on the heat treatment atmosphere. No multistage transformation occurs when the evaporation of Ti and/or Ni and the preferential oxidation of Ti are prevented by the purification of the heat treatment atmosphere in an evacuated quartz tube by a Ti-getter. The heterogeneity in precipitation morphology of the Ti3Ni4 phase, which is responsible for the multistage transformation, can thus be suppressed. The influence of changes in the Ni concentration and specimen size on the multistage transformation is also discussed. The multistage transformation is not detected in the concentrated Ni alloy such as Ti-51.4 at.% Ni. All the results obtained in the present study are consistently explained by assuming the formation of zones I and II. The zone I is considered to be a contamination region with interstitial impurity elements, which is responsible for the multistage transformation. The zone II is considered to be a zone of relatively higher Ni concentration as compared to the original alloy composition at the surface..
95. M. Nagasako, Minoru Nishida, Yasukazu Murakami, D. Shindo, Martensitic and order-disorder transformations in Ti45Pd45Ni10 alloy, Materials Science and Engineering A, 10.1016/j.msea.2005.12.065, 438-440, SPEC. ISS., 848-851, 2006.11, Transformation sequence and behavior in Ti45Pd45Ni10 alloy (numbers indicate at.%) have been investigated. The solution treated alloy shows reverse martensitic transformation from B19 to B2 structure, B2 to long period stacking order (LPSO) structure, LPSO to B2 structure and precipitation of Ti3(PdNi)4 and Ti2(PdNi)3 phases successively upon heating. The above transformation sequence is confirmed by electrical resistivity measurements and in situ electron diffraction experiments. The martensitic transformation is suppressed by the formation of LPSO phase. Morphology and crystallography of the LPSO phase are also discussed briefly..
96. T. Nishiura, T. Yamamuro, D. Hashimoto, Y. Morizono, Minoru Nishida, Martensitic transformation and phase equilibrium in near equiatomic Zr-Pd alloys, Materials Science and Engineering A, 10.1016/j.msea.2006.02.144, 438-440, SPEC. ISS., 852-856, 2006.11, Martensitic transformation behavior and phase equilibrium in Zr-Pd alloys have been investigated. Near equiatomic Zr-Pd alloys quenched from above 1073 K undergo a martensitic transformation at around 830 K. However, the ZrPd compound transforms to Zr13Pd12 and Zr9Pd11 compounds by a eutectoid reaction at about 1040 K. It is also found that the Zr13Pd12 compound forms by a peritectoid reaction between Zr2Pd and ZrPd at about 1100 K. A modified equilibrium phase diagram between Zr2Pd and Zr3Pd4 in the Zr-Pd binary system is proposed..
97. Y. Sutou, K. Yamauchi, T. Takagi, T. Maeshima, Minoru Nishida, Mechanical properties of Ti-6 at.% Mo-4 at.% Sn alloy wires and their application to medical guidewire, Materials Science and Engineering A, 10.1016/j.msea.2006.01.116, 438-440, SPEC. ISS., 1097-1100, 2006.11, Effects of heat treatment conditions on mechanical and superelastic properties of Ti-6 at.% Mo-4 at.% Sn alloy were investigated mainly by cyclic tensile testing. The cold-drawn wires were heat-treated in the temperature range of 773-1273 K for 300 s. Young's modulus and ultimate tensile strength of the wires heat-treated at over 823 K decreased with increasing heat treatment temperature, while premature failure was observed in the wire heat-treated at 773 K. A maximum recovery strain of about 4%, including both genuine elastic and superelastic strain, was obtained in the wires heat-treated in the temperature range of 1073-1273 K. On the other hand, the wire heat-treated at 823 K showed a high Young's modulus of 77 GPa and a high tensile strength of 1698 MPa. Given these characteristics, it is expected that a new class of Ni-free Ti-based guidewire possessing mechanical properties graded from the tip to the end can be developed..
98. M. Matsuda, D. Hashimoto, V. C. Solomon, Minoru Nishida, Morphology and crystallography of Ti2Pd phase precipitated in B2 parent and B19 martensite matrices in Ti-rich Ti-Pd alloys, Materials Science and Engineering A, 10.1016/j.msea.2006.01.126, 438-440, SPEC. ISS., 821-824, 2006.11, Morphology and crystallography of Ti2Pd phase of C11b structure precipitated in B2 parent and B19 martensite matrices in Ti-rich Ti-Pd shape memory alloy have been investigated by transmission electron microscopy observations. Three Ti2Pd variants were recognized in the specimen aged above Af temperature, i.e., in the B2 matrix. On the other hand, four Ti2Pd variants were confirmed in the specimen aged below As temperature, i.e., in the B19 matrix. The orientation relationship between the Ti2Pd precipitate and each matrix is consistent with the number of Ti2Pd variants. The Ti2Pd precipitates in the B2 and the B19 matrices have a disk and a polygonal plate shapes, respectively. The c-axis of Ti2Pd precipitate in the B2 matrix is perpendicular to the disk surface. On the other hand, that in the B19 matrix is parallel to the plate surface. These differences are well explained by the magnitude of coherent strain..
99. T. Yamamuro, Y. Morizono, J. Honjyo, Minoru Nishida, Phase equilibrium and martensitic transformation in near equiatomic Ti{single bond}Pd alloys, Materials Science and Engineering A, 10.1016/j.msea.2006.01.120, 438-440, SPEC. ISS., 327-331, 2006.11, The homogeneity range of the TiPd compound is experimentally determined from martensitic transformation behaviors of solution treated and aged specimens with various compositions and diffusion couple method, and then the phase diagram of Ti{single bond}Pd binary system in Ti side is reinvestigated. The phase boundary of TiPd compound on the Pd side is almost constant at about 50.5 at.% Pd. On the other hand, that on the Ti side extends from 50.6 at.% Ti at around 873 K to about 51.8 at.% Ti at 1073 K. From the diffusion couple experiments, it is recognized that there is an A2(bcc) to B2 order-disorder transformation around 30 at.% Pd instead of a β-Ti and TiPd duplex phase region. It is also confirmed that the Ti3Pd compound is formed by a peritectoid reaction between β-Ti and Ti2Pd. From these results, we propose a new phase diagram of the Ti{single bond}Pd binary system..
100. Y. Sutou, K. Yamauchi, M. Suzuki, A. Furukawa, T. Omori, T. Takagi, R. Kainuma, Minoru Nishida, K. Ishida, High maneuverability guidewire with functionally graded properties using new superelastic alloys, Minimally Invasive Therapy and Allied Technologies, 10.1080/13645700600836109, 15, 4, 204-208, 2006.08, Nitinol shape memory alloys (SMAs) are attracting considerable attention as core materials for medical guidewires because of their excellent flexibility and shape retention. However, since Nitinol guidewires possess low rigidity, the pushability and torquability of the guidewires are insufficient. On the other hand, although guidewires made of stainless steel have high pushability, plastic deformation occurs easily. We have developed a new class of superelastic guidewires with functionally graded properties from the tip to the end by using new SMA core materials such as Cu-Al-Mn-based or Ni-free Ti-Mo-Sn SMAs. The tip portion of the guidewire shows excellent superelasticity (SE), while the body portion possesses high rigidity. These functionally graded characteristics can be realized by microstructural control. These guidewires with functionally graded properties show excellent pushability and torquability and are considerably easier to handle than conventional guidewires with Nitinol or stainless steel cores. Moreover, a metallic catheter using a Ni-free Ti-based SMA with high biocompatibility is introduced..
101. Mitsuhiro Matsuda, Shinji Ando, Yoshihito Kawamura, Minoru Nishida, Deformation structure in rapidly solidified Mg97Zn 1y2 alloy with long period stacking order phase, Memoirs of the Faculty of Engineering, Kumamoto University, 50, 1, 31-40, 2006.03, Deformation structure in rapidly solidified Mg97Zn 1Y2 ribbon with the long period stacking order (LPSO) phase is investigated by conventional transmission electron microscopy to understand the interaction between the LPSO phase and lattice defects. In the grain with the LPSO phase there are no a dislocations lying on the basal plane, and a number of c + a dislocations are visible. On the other hand, in the grain without the LPSO phase there are many straight a dislocations lying on the basal plane. These facts indicate that the critical resolved shear stress of the basal plane increases by the formation of the LPSO phase and the non-basal slip is activated by the prevention of the basal slip. In other words, the former directly contributes to the strengthening and the latter relates to the improvement of ductility with the increment of the slip system. Therefore, it is concluded that the LPSO phase plays a unique role which enhances the conflicting properties of strength and ductility in the mechanical property of the present alloy. The densely developed LPSO phase prevents the growth of {101̄2} deformation twin in Mg matrix. This indicates that the LPSO phase contributes to the strengthening of this alloy. On the other hand, the LPSO phase with low density cannot be the resistance of the twinning. The trace of basal plane in such LPSO phase deviates with constant angle of about 3.8 degrees at the twin boundary. This angle is well explained by the atomic movement with shuffling in the formation of {101̄2} twin..
102. Minoru Nishida, Kentarou Ishiuchi, Kousuke Fujishima, Toru Hara, Effect of heat treatment atmosphere on multistage R-phase transformation in an aged Ti-51.0at%Ni alloy, Materials Transactions, 10.2320/matertrans.47.645, 47, 3, 645-649, 2006.03, The present study systematically investigates the effect of heat treatment atmosphere on the multistage R-phase transformation (MRT) in an aged Ti-51.0 at%Ni alloy. No MRT occurs when the heat treatments were completed under the regulated atmosphere. On the other hand, the MRT is observed in the specimen heat treated under the unregulated atmosphere. It is apparent from transmission electron microscope observations that the first and the second transformations take place around the grain boundary and at the grain interior, respectively. We conclude that the MRT is extrinsic, and is an artifact during the heat treatment, rather than intrinsic in nature..
103. Takashi Maeshima, Satoshi Ushimaru, Kiyoshi Yamauchi, Minoru Nishida, Effects of Sn content and aging conditions on superelasticity in biomedical Ti-Mo-Sn alloys, Materials Transactions, 10.2320/matertrans.47.513, 47, 3, 513-517, 2006.03, The effects of Sn content and aging conditions on superelasticity in Ti-Mc-Sn alloys were investigated. Martensitic transformation temperature decreased with an increasing of Sn content. A large superelastic strain of 3.0% was obtained in a solution-treated Ti-5 mol%Mo-5 mol%Sn alloy in the tensile test. The superelasticity in the Ti-5 mol%Mo-5 mol%Sn at room temperature was improved by aging at 873 K for short periods between 180 and 420 s. A specimen aged at 873 K for 300 s exhibited superelasticity with a recovery strain of 3.5% in the tensile test. A recovery strain of 3.0% was consistently achieved in cyclic tensile deformations..
104. Shuichi Miyazaki, Tomoyuki Kakeshita, Toshio Sakuma, Minoru Nishida, Yasubumi Furuya, Hideki Hosoda, Special issue on shape memory alloys and their applications, Materials Transactions, 47, 3, 504, 2006.03.
105. T. Kono, Minoru Nishida, Y. Nishiki, Y. Seki, K. Sato, Y. Akiba, Characterisation of glucose transporter (GLUT) gene expression in broiler chickens, British Poultry Science, 10.1080/00071660500181289, 46, 4, 510-515, 2005.08, 1. Glucose transporter (GLUT) proteins, one of which is the major insulin-responsive transporter GLUT4, play a crucial role in cellular glucose uptake and glucose homeostasis in mammals. The aim of this study was to identify the extent of mRNA expression of GLUT1, GLUT2, GLUT3 and GLUT8 in chickens intrinsically lacking GLUT4. 2. GLUT1 mRNA was detected in most tissues of 3-week-old broiler chickens, with the highest expression measured in brain and adipose tissue. GLUT2 was expressed only in the liver and kidney. GLUT3 was highly expressed in the brain. GLUT8 was expressed ubiquitously, with expression in kidney and adipose tissue relatively higher than that of other tissues. 3. Expression levels of GLUT isoforms 1, 3 and 8 in skeletal muscle tissue were very low compared to the other tissues tested. 4. [3H]Cytochalasin B binding assays on tissue from 3-week-old chickens showed that the number of cytochalasin B binding sites in skeletal muscle plasma membranes was higher than in liver plasma membranes. These results suggest that GLUT proteins and/or GLUT-like proteins that bind cytochalasin B are expressed in chicken skeletal muscles. 5. It is proposed that GLUT expression and glucose transport in chicken tissues are regulated in a manner different from that in mammals..
106. Minoru Nishida, Toru Hara, Yasuhiro Morizono, Mitsuhiro Matsuda, Kousuke Fujishima, Effect of heat treatment conditions on multistage martensitic transformation in aged Ni-rich Ti-Ni alloys, 2004 MRS Fall Meeting Materials Research Society Symposium Proceedings, 842, 365-370, 2005.08, It has been demonstrated with systematic experiments that the appearance and disappearance of multistage martensitic transformation (MMT) in aged Ni-rich Ti-Ni alloys depend on the heat treatment conditions. No multistage transformation occurs when the evaporation of Ti and Ni and/or the preferential oxidation of Ti in the specimen are prevented and the purification of heat treatment atmosphere in an evacuated quartz tube is achieved. The heterogeneity in precipitation morphology of the Ti3Ni4 phase, which is responsible for the multistage transformation can be suppressed with the regulation of heat treatment atmosphere as mentioned above. We have concluded that the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys is extrinsic in nature, and is an artifact during the heat treatment..
107. Takashi Maeshima, Satoshi Ushimaru, Kiyoshi Yamauchi, Minoru Nishida, Effects of Sn content and aging conditions on superelasticity in biomedical Ti-Mo-Sn alloys, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.69.654, 69, 8, 654-658, 2005.08, The effects of Sn content and aging conditions on superelasticity in Ti-Mo-Sn alloys were investigated. Martensitic transformation temperature decreased with an increasing of Sn content. A large superelastic strain of 3.0% was obtained in a solutiontreated Ti-5 mol%Mo-5 mol%Sn alloy in the tensile test. The superelasticity in the Ti-5 mol%Mo-5 mol%Sn at room temperature was improved by aging at 873 K for short periods between 180 and 420 s. A specimen aged at 873 K for 300 s exhibited superelasticity with a recovery strain of 3.5% in the tensile test. A recovery strain of 3.0% was consistently achieved in cyclic tensile deformations..
108. S. Nakamichi, S. Tsurekawa, Y. Morizono, T. Watanabe, Minoru Nishida, A. Chiba, Diffusion of carbon and titanium in γ -iron in a magnetic field and a magnetic field gradient, Journal of Materials Science, 10.1007/s10853-005-2683-3, 40, 12, 3191-3198, 2005.06, The diffusion coefficients of carbon and titanium in γ -iron were measured in a 6T magnetic field and in magnetic field gradients ranging from 30 to 45 T/m. We have found that the diffusion of carbon in γ -iron is retarded by application of a 6T magnetic field. In contrast with carbon diffusion, no noticeable effect of a magnetic field on the diffusivity of titanium in γ -iron is observed. On the other hand, the diffusion of carbon in γ -iron can be enhanced in a magnetic field gradient when carbon atoms move towards the direction with a higher magnetic field strength. The higher the magnetic field gradient strength becomes, the more the carbon diffusion is enhanced. Nevertheless, a magnetic field gradient causes a decrease in diffusivity of carbon in γ -iron when the opposite magnetic field gradient is applied..
109. Mitsuhiro Matsuda, Shinji Ando, Minoru Nishida, Dislocation structure in rapidly solidified Mg97Zn 1Y2 alloy with long period stacking order phase, Materials Transactions, 10.2320/matertrans.46.361, 46, 2, 361-364, 2005.02, Dislocation structure in rapidly solidified Mg97Zn 1Y2 ribbon with the long period stacking order (LPSO) phase is investigated by conventional transmission electron microscopy. In the grain with the LPSO phase there are no a dislocations lying on the basal plane, and a number of c + a dislocations are visible. On the other hand, in the grain without the LPSO phase there are many straight a dislocations lying on the basal plane. These facts indicate that the critical resolved shear stress of the basal plane increases by the formation of the LPSO phase and the non-basal slip is activated by the prevention of the basal slip. In other words, the former directly contributes to the strengthening and the latter relates to the improvement of ductility with the increment of the number of the slip system. Therefore, it is concluded that the LPSO phase plays a unique role which overcomes the conflicting properties of strength and ductility in the mechanical property of the present alloy..
110. M. Matsuda, S. Ii, Y. Kawamura, Y. Ikuhara, Minoru Nishida, Variation of long-period stacking order structures in rapidly solidified Mg97Zn1Y2 alloy, Materials Science and Engineering A, 10.1016/j.msea.2004.10.040, 393, 1-2, 269-274, 2005.02, The long-period stacking order (LPSO) structures in rapidly solidified Mg97Zn1Y2 alloy have been studied by conventional and high-resolution transmission electron microscopes (HRTEMs). There are four kinds of stacking sequences in the LPSO structures, i.e., 18R of ABABABCACACABCBCBC, 14H of ACBCBABABABCBC, 10H of ABACBCBCAB and 24R of ABABABABCACACACABCBCBCBC. The 18R structure is dominantly observed in the present study. The rest three are occasionally observed in places. The 10H and 24R structures are recently discovered. The lattice constants of 18R(1 1̄ 1 1̄ 2)3), 14H(2̄ 1 2̄ 1 1̄ 1 1̄ 2 1̄ 2), 10H(1 3̄ 1 1̄ 3 1̄) and 24R(1 1̄ 1 1̄ 1 1̄ 2)3 structures are estimated to be a = 0.320 nm and c = 4.678 nm, a = 0.325 nm and c = 3.694 nm, a = 0.325 nm and c = 2.603 nm, a = 0.322 nm and c = 6.181 nm for the hexagonal structure, respectively..
111. Yasuhiro Morizono, Masayuki Muto, Minoru Nishida, Takao Asada, Takateru Yamamuro, Akira Chiba, Solid state bonding of oxide dispersion strengthened silver to copper, Yosetsu Gakkai Ronbunshu/Quarterly Journal of the Japan Welding Society, 10.2207/qjjws.23.296, 23, 2, 296-301, 2005.01, Diffusion bonding and explosive welding of oxide dispersion strengthened silver (ODS-Ag), which is one of electric contact materials, to copper (Cu) have been conducted to compare their interfacial microstructures and bonding strength. The diffusion bonding was carried out at 973 K for 3.6 ks to achieve solid state bonding. Defects like void were observed at the interface in the diffusion bonded ODS-Ag/Cu joint. It is considered that insufficient contact at the interface is responsible for the formation of the defects. The shear strength of this joint was less than 40 MPa and far inferior to that of Ag/Cu joint produced under the same condition. On the other hand, the explosively welded joint had no defects in the collision interface. Its bonding strength exceeded that of the diffusion bonded Ag/Cu joint, and was about four times as high as that of the ODS-Ag/Cu joint fabricated by diffusion bonding. From the results of TEM observations, microstructural aspects of the ODS-Ag in the vicinity of the collision interface appear to be similar to those observed before bonding. This suggests that the characteristics of the ODS-Ag as a electric contact material are retained even after the bonding treatment. Therefore, the solid state bonding with momentary high pressure such as explosive welding is suited to the bonding method for the ODS-Ag materials..
112. Minoru Nishida, Mituhiro Matsuda, Yasuhiro Morizono, Towako Fujimoto, Hideharu Nakashima, Application of the CSL model to deformation twin boundary in B2 Type TiNi compound, Unknown Journal, 842, 371-376, 2005, The deformation structure of B2 type TiNi compound around 573 K has been investigated by transmission electron microscopy (TEM). Serrations are seen in stress-strain curve, which corresponds to the formation of various planar defects with twin relation. The dominant planar defect found in the specimens showing serration is {114} compound twin. The other defects are in mirror symmetry with respect to {113}, {115}, {447} planes and so on. These defects are considered to be 〈110〉 symmetric tilt boundaries in bcc structure by ignoring the atomic arrangement of B2 structure and are characterized with ∑ value based on coincide site lattice (CSL) model. For instance, the ∑ value of {114}, {113}, {115} and {447} boundaries are ∑9, ∑11, ∑27 and ∑81, respectively. Numerous (114) defects initially form at grain boundary and grow into grain interior, Some of those deflect to (-1-14) defects. In such case, the {447} ∑81defect is always observed at the interface of (114) ∑9 and (-1-14) ∑9 defects. This fact indicates that the sigma combination rule of the CSL model can be applied to the triple junction of defects. Similarly, {7710} ∑99 boundary forms at the interface of {114} ∑9 and {113} ∑11 defects. It can be concluded that the ductility of B2 type TiNi compound around 573 K is attributable to the formation of various planar defects with large shear strain and the increment of independent slip system due to the formation of planar defects, and that the arrangement of some planar defects conforms to the sigma combination rule of CSL model..
113. Minoru Nishida, Mitsuhiro Matsuda, Daisuke Hashimoto, C11b type precipitates in B2 parent and B19 martensitic matrices in Ti-Pd alloy, International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2005 Proceedings of an International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2005, 2, 81-86, 2005, The morphology and crystallography of the Ti2Pd phase with C11b structure precipitated in B2 parent and B19 martensitic matrices in a Ti-rich Ti-Pd shape memory alloy have been investigated by transmission electron microscopy. Three Ti2Pd variants are recognized in the specimen aged above the Af temperature, i.e., in the B2 matrix. On the other hand, four Ti2Pd variants are confirmed in the specimen aged below the As temperature, i.e., in the B19 matrix. The ori.entation relationship between the Ti2Pd precipitate and each matrix is consistent with the number of Ti2Pd variants. The Ti 2Pd precipitates in the B2 and the B19 matrices have disk and polygonal plate shapes, respectively. The c-axis of Ti2Pd precipitate in the B2 matrix is perpendicular to the disk surface. On the other hand, that in the B19 matrix is parallel to the plate surface. These differences are well explained by the magnitude of the coherent strain..
114. Minoru Nishida, Yasuhiro Morizono, Kousuke Fujishima, Kentarou Ishiuchi, Effect of heat treatment conditions on multistage R and martensitic transformations in aged Ni-rich Ti-Ni alloys, International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2005 Proceedings of an International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2005, 2, 139-144, 2005, It has been demonstrated with systematic experiments that the appearance and disappearance of multistage martensitic transformation (MMT) in aged Ni-rich Ti-Ni alloys depend on the heat treatment atmosphere. No multistage transformation occurs when the evaporation of Ti and/or Ni and the preferential oxidation of Ti are prevented and the purification of heat treatment atmosphere in an evacuated quartz tube is achieved. The heterogeneity in precipitation morphology of the Ti3Ni4 phase, which is responsible for the multistage transformation, can be suppressed with the regulation of heat treatment atmosphere as mentioned above. We have concluded that the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys is extrinsic, and is an artifact during the heat treatment, rather than intrinsic in nature. Effect of heat treatment condition on the multistage R-phase transformation (MRT) is also discussed..
115. Yasuhiro Morizono, Minoru Nishida, Akira Chiba, Takateru Yamamuro, Effect of heat treatment on formation of columnar ferrite structure in explosively welded titanium/hypoeutectoid steel joints, Proceedings of the 1st International Symposium on Explosion, Shock Wave and Hypervelocity Phenomena (ESHP Symposium) Materials Science Forum, 465-466, 373-378, 2004.11, Explosive welding of titanium to hypoeutectoid steel (0.09 mass%C) was carried out, and interfacial aspects of as-welded and heat treated states have been investigated with a focus on microstructures of the steel. In as-welded joint, plastic flow occurred by high velocity collision was observed in the vicinity of the interface. The steel in the joints retained equiaxed structure consisting of ferrite and pearlite even after prolonged heat treatment up to 1173 K. Columnar grains were generated in the steel near the interface by the heat treatment at 1223 K and above. Although the region of the columnar ferrite structure increased with increasing heating temperature and holding time, texture with specific crystal orientation was not confirmed. It was found that such a microstructural change in the steel was closely related to constituent phases formed at the bonding interface. The formation mechanism of the columnar structure was also discussed..
116. M. Matsuda, S. Ii, Y. Kawamura, Y. Ikuhara, Minoru Nishida, Interaction between long period stacking order phase and deformation twin in rapidly solidified Mg97Zn1Y2 alloy, Materials Science and Engineering A, 10.1016/j.msea.2004.08.006, 386, 1-2, 447-452, 2004.11, Interaction between long period stacking order (LPSO) phase and {1 0 1̄ 2} deformation twin in rapidly solidified Mg97Zn1Y2 alloy is investigated. The densely developed LPSO phase prevents the growth of {1 0 1̄ 2} deformation twin in Mg matrix. On the other hand, the LPSO phase with low density cannot be the resistance of the twinning. The trace of basal plane in such LPSO phase deviates with constant angle of about 3.8° at the twin boundary. This angle is well explained by the atomic movement with shuffling in the formation of {1 0 1̄ 2} twin. The interfacial microstructure of {1 0 1̄ 2} deformation twin is also discussed on the basis of high resolution electron microscopy (HREM)..
117. Akira Chiba, Minoru Nishida, Yasuhiro Morizono, Microstructure of bonding interface in explosively-welded clads and bonding mechanism, Proceedings of the 1st International Symposium on Explosion, Shock Wave and Hypervelocity Phenomena (ESHP Symposium) Materials Science Forum, 465-466, 465-474, 2004.11, Microstructural aspects and bonding characteristics of the explosive welded Ti/Ti, Ti/steel and Ti/Ni clads were investigated mainly by TEM microscopy. It was found that the bonding interface was composed of layers of metastable phases such as amorphous phases, icosahedral quasicrystal and intermetallic compounds. These metastable phases are formed as a trace of melting followed by subsequent rapid solidification of thin layers of about 200 nm in thickness along the contact surface of both the component materials. It is concluded that the very thin melting layer is responsible for the bonding of explosively welded Ti base clads and especially amorphous phase formed in the bonding interface keeps high bonding strength..
118. Minoru Nishida, Yoshihito Kawamura, Takateru Yamamuro, Formation process of unique microstructure in rapidly solidified Mg97Zn1Y2 alloy, Materials Science and Engineering A, 10.1016/j.msea.2003.10.145, 375-377, 1-2 SPEC. ISS., 1217-1223, 2004.07, The formation process of 6H-phase in rapidly solidified powder metallurgy (RS P/M) Mg97Zn1Y2 alloy has been investigated by transmission electron microscopy (TEM) observations. The initial microstructure of RS powder consists of equiaxed grains about 1μm in average diameter which is surrounded by Y and Zn rich amorphous grain boundaries. The 6H-phase was observed at grain boundaries in the RS ribbon prepared at circumferential speed of 42m/s. By lowering the circumferential speed, the 6H-phase at grain boundary in the RS ribbon changes to amorphous phase. The amount of Y and Zn segregation at the grain boundary in RS Mg97Zn1Y2 alloy increases with decreasing the cooling rate. In other words, the amorphization of grain boundary phase in RS alloy was promoted by the enrichment of Y and Zn. The growth of 6H-phase starts from grain boundary in the RS ribbon annealed at 573K for 1.2ks. It can be concluded that the 6H-phase in RS P/M Mg97Zn1Y2 alloy crystallizes in the Y and Zn rich amorphous phase at grain boundary and then grows into grain interior during extrusion. In order to clarify the stability of 6H-phase with heat treatment, microstructure changes in RS ribbon are also described..
119. Takashi Maeshima, Minoru Nishida, Shape memory and mechanical properties of biomedical Ti-Sc-Mo alloys, Materials Transactions, 10.2320/matertrans.45.1101, 45, 4, 1101-1105, 2004.04, Ni-free Ti-Sc-Mo shape memory alloys are designed as a substitute for Ti-Ni alloys in the biomedical field. From results of bending and recovery test with heating, Ti-Sc-Mo alloys were found to have superior shape memory effect. The optimum composition for the shape memory effect was Ti-4.0 to 6.0Sc-6.0Mo alloys. The maximum shape recovery strain in the Ti-5.0Sc-6.0Mo alloy was 5.3% measured through cyclic tensile deformation. Vickers hardness and 0.2% proof stress were remarkably decreased and elongation was increased with Sc content. The marked grain refining was also achieved. The relationship between microstructure and mechanical properties was briefly discussed. Microstructure observations and XRD measurements before and after tensile deformation showed that the shape memory effect was associated with the stress induced βto α″ transformation..
120. Takashi Maeshima, Minoru Nishida, Shape memory properties of biomedical Ti-Mo-Ag and Ti-Mo-Sn alloys, Materials Transactions, 10.2320/matertrans.45.1096, 45, 4, 1096-1100, 2004.04, Shape memory properties of Ti-Mo-Ag and Ti-Mo-Sn alloys consisting of biocompatible elements were investigated. The alloys with appropriate combination of Mo and Ag or Sn showed nearly perfect shape memory effect in convenient bending and heating tests. Recoverable tensile strain is more than 3% in some of Ti-Mo-Ag and Ti-Mo-Sn alloys. Microstracture observations and X-ray diffraction measurements before and after tensile test revealed that stress induced β to α″ martensitic transformation was origin of the shape memory effect..
121. Yasuhiro Morizono, Minoru Nishida, Akira Chiba, Takateru Yamamuro, Yusuke Kanamori, Takanobu Terai, Diffusion Bonding of TiAl Alloy to Eutectoid Steel and its Interfacial Self-destruction Behavior, Materials Transactions, 10.2320/matertrans.45.527, 45, 2, 527-531, 2004.01, Interfacial microstructures and bonding strength of TiAl alloy/eutectoid steel joints have been investigated from the viewpoint of diffusion barrier effect of carbide layer formed at the interface. Diffusion bonding was performed at 1073 to 1273 K for 3.6 ks in a vacuum, and then several specimens were heated at 1073 to 1273 K for 10.8 to 86.4 ks in evacuated quartz tube to examine the growth behavior of reaction layer. The joint has essentially four kinds of the reaction layers. They are composed of two layers with Ti, Al and Fe elements, TiC layer containing Fe-Al compounds and ferrite layer. This indicates that the joint is difficult to have stable diffusion barrier layer consisting only of the TiC due to contribution of Al element to the interfacial reaction. Although the joint bonded at 1073 K shows high bonding strength of 160 MPa, the strength dramatically decreases with increasing bonding temperature. In addition, self-destruction phenomenon is recognized at the interface in the joints heat-treated at 1173 and 1273 K, and the origin is also discussed..
122. Yasuhiro Morizono, Minoru Nishida, Akira Chiba, Takashi Nakata, Interfacial microstructures and bonding strength between aluminum nitride and silver brazing filler metals containing various active elements, Journal of the Ceramic Society of Japan, 10.2109/jcersj.112.305, 112, 1306, 305-310, 2004.01, Effect of active element on interfacial microstructures and bonding strength of brazed AIN/AIN joints has been investigated and compared with the case of brazed Si3N4/Si3N4 joints. Brazing was carried out at 1173 to 1473 K for 3.6 ks in a vacuum using Ag-Cu filler metals containing Ti, Zr, V and Nb as an active element. The obtained joint had no defects such as un-bonded areas, regardless of active element and bonding temperature. Four kinds of active elements were divided into two groups by shear tests and microstructural observations. One was Ti and Zr, and the other was V and Nb. The bonding strength of the former was higher than that of the latter. In particular, the joint with Ti addition showed an excellent strength of about 200 MPa. Main fracture position in the joints with Ti and Zr additions was within the AIN, while most joints with V and Nb additions broke at the interface between the active filler metal and the AIN. In the former, TiN and ZrN layers consisting of fine grains were observed adjacent to the AIN. On the other hand, the joint with Nb addition had roundish grains of Nb 2N in similar locations. It was considered that the existence of fine grains contributed to the enhancement of bonding strength due to the increase of contact area and to the formation of complicated interface. These tendencies were essentially consistent with those of the brazed Si3N 4/Si3N4 joints..
123. S. Ii, K. Yamauchi, Y. Maruhashi, Minoru Nishida, Direct evidence of correlation between {2 0 1̄}B19′ and {1 1 4}B2 deformation twins in Ti-Ni shape memory alloy, Scripta Materialia, 10.1016/S1359-6462(03)00356-7, 49, 7, 723-727, 2003.10, The correlation between {201̄}B19′ and {114}B2 deformation in Ti-NI shape memory alloys was discussed. It was found that the stress-strain curve of Ti-50.6at%Ni alloy, deformed at 240 K was divided into three stages, which were same as those in Ti-50.0at%Ni alloy. It was confirmed that there is the continuity of K1 planes between the two twinning systems..
124. S. Li, Minoru Nishida, Yasukazu Murakami, D. Shindo, Martensitic transformation in Ti50Pd50-xFex alloy, Journal De Physique. IV : JP, 112 II, 1035-1038, 2003.10, In order to clarify the transformation sequence in Ti50.0Pd50.0-XFeX alloy in detail, in-situ heating TEM observations and electron diffraction experiments were carried out in JEM-2010 microscope equipped with omega type energy-filter. Mf temperature of Ti50.0Pd43.0Fe7.0 alloy is about 520 K and martensite of 2H and 9R structures are observed at room temperature. The 9R martensite directly reverts to the B2 parent phase via no intermediate state. Only incommensurate (IC) phase is confirmed at room temperature in Ti50.0Pd40.0Fe10.0 and Ti50.0Pd36.0Fe14.0 alloys, although Mf temperatures of these alloys are above room temperature. The IC phase transforms to the B2 parent phase without any shift of intensity maximum position of IC reflections with heating. Therefore, the low temperature phase in the alloys with more than 8.0 at% of Fe is the IC phase. Based on these results, systematical transformation phase diagram is proposed..
125. Minoru Nishida, K. Tanaka, S. Ii, M. Kohshima, S. Miura, M. Asai, Microstructure modifications by tensile deformation in Ti-Ni-Fe alloy, International Conference on Martensitic Transformations Journal De Physique. IV : JP, 112 II, 803-806, 2003.10, The origin of anomalous ductility in Ti-Ni alloy systems has been investigated by using Ti50Ni48Fe2 with tensile tests at wide temperature range about 200 to 800 K and TEM observations. The advantage of the alloy used is that there is no decomposition during tensile test at elevated temperature. Tensile stress-strain curve is divided into three types. Below 400 K tensile deformation behavior relates to stess and or strain induced martensitic transformation. Between 400 and 700 K serration is observed in stress-strain curve, which is derived from the formation of various deformation twins with rather large twinning shear. Anomalous ductility is attribute to the formation of these twins and increment of slip system. Above 700 K necking take place during tensile test and only dislocations are seen in the deformed specimen. However, type of burgers vector dose not change with deformation temperature throughout the present study..
126. V. C. Solomon, Minoru Nishida, Morphological and crystallographic aspects of C11b-type precipitates nucleated in martensitic and parent phase matrices in Ti-rich Ti-Pd shape memory alloys, Unknown Journal, 112 II, 1039-1042, 2003.10, Ti2Pd phase with C11b-type structure which precipitates in Ti-rich Ti-Pd shape memory alloys may nucleate either in martensitic phase or parent phase depending upon thermal treatment conditions, since the transformation temperatures are around 800 K. In the alloy aged above Af, three C11b-type precipitate variants are always observed by TEM. The orientation relationship between those three variants and the B19 structure, which was transformed from B2 structure after the precipitation, is as follows: Variant I (001)Ti2Pd// (101̄)B19; Variant II (001)Ti2Pd// (101)B19; Variant III (001)Ti2Pd// (010)B19. The shape of the precipitates was deduced to be disk-like and/or elliptic. On the other hand, only the variants I and II are observed when the precipitates are nucleated in martensitic phase. Since the difference between the lattice spacing of (010)B19 and (001)/3Ti2Pd is about 20%, the formation of a third variant in the martensitic matrix is energetically unfavorable..
127. M. Nagasako, Minoru Nishida, Phase transformations in Pd- and Ni-rich Ti-Pd-Ni alloys, Unknown Journal, 112 II, 1043-1046, 2003.10, It has been found that Ti45Pd45Ni10 alloy shows peculiar phase transformations. Upon heating in DSC measurement, an endothermic reaction occurs firstly around 373 K, which corresponds to the reverse martensitic transformation from B19 to B2 structure. Subsequently, a pair of exothermic and endothermic peaks is observed from 550 to 740 K, which is due to the appearance and disappearance of new order phase with long period stacking structure. One of characteristic feature in electron diffraction pattern of the new phase is superlattice spots at 1/8 position in the row of reflections of 111B2*. Finally, an exothermic reaction which corresponds to the formation of Ti2(PdNi)3 phase is detected around 850 K. More interesting phenomenon, which is the parent phase stabilization with low temperature aging below 500 K, is discovered. The ω-like diffuse reflections with rather strong intensity are observed in electron diffraction patterns taken from the stabilized B2 phase. Morphological and crystallographic aspects of the new order phase are also discussed..
128. Minoru Nishida, T. Yamamuro, M. Nagano, Y. Morizono, Y. Kawamura, Electron microscopy study of microstructure modifications in RS P/M Mg97Zn1Y2 alloy, Proceedings of the Second Osaka International Conference on Platform Science and Technology for Advanced Magnesium Alloys 2003 Materials Science Forum, 419-422, II, 715-720, 2003.04, In order to clarify the formation process of 6H-phase in RS P/M Mg97Zn1Y2 alloy, transmission electron microscopy (TEM) observations have been carried out. The initial microstructure of RS powder consists of cellular structure. The equiaxed grains about 1 μm in average diameter are surrounded by rather wide Y and Zn rich amorphous grain boundaries. 6H-phase was observed at grain boundaries in the RS ribbon prepared at circumferential speed of 42 m/s. By lowering the circumferential speed, the 6H-phase at grain boundary in the RS ribbon changes to amorphous phase. The growth of 6H-phase starts from grain boundary in the RS ribbon annealed at 573 K for 1.2 ks. It can be concluded that the 6H-phase in RS P/M Mg97Zn1Y2 alloy crystallizes in the Y and Zn rich amorphous phase at grain boundary and then grows into grain interior during extrusion..
129. Kenshi Inoue, Yoshihito Kawamura, Minoru Nishida, Rapidly solidified Mg-(Ag, Sc)-X alloys with high strength, Proceedings of the Second Osaka International Conference on Platform Science and Technology for Advanced Magnesium Alloys 2003 Materials Science Forum, 419-422, II, 757-762, 2003.04, The structure and mechanical properties of ternary Mg-(Sc, Ag)-X (X= Al, Ca, Zn, Y, Mn, Sn and Si) rapidly solidified (RS) ribbons were investigated. Alloy compositions having the best-combined properties of ductility and hardness (> Hv110) were a Mg97Sc1Y2 alloy in Mg-Sc-X system and a Mg96.5Ag0.5Y3 alloy in Mg-Ag-X system. It is expected that the RS powder metallurgy alloys having a high yield strength above 600 MPa and an elongation above 5 % can be developed in the Mg97Sc1Y2 and Mg96.5Ag0.5Y3 compositions..
130. Minoru Nishida, Toru Hara, Takuya Ohba, Koichi Yamaguchi, Koichi Tanaka, Kiyoshi Yamauchi, Experimental consideration of multistage martensitic transformation and precipitation behavior in aged Ni-rich Ti-Ni shape memory alloys, Materials Transactions, 10.2320/matertrans.44.2631, 44, 12, 2631-2636, 2003.01, It has been demonstrated with systematic experiments that the appearance and disappearance of multistage martensitic transformation in aged Ni-rich Ti-Ni alloys depend on the heat treatment atmosphere. No multistage transformation occurs when the evaporation of Ti and Ni and/or the preferential oxidation of Ti in the specimen are prevented and the purification of heat treatment atmosphere in an evacuated quartz tube is achieved. The heterogeneity in precipitation morphology of Ti
3
Ni
4
phase which is responsible for the multistage transformation can be suppressed with the regulation of heat treatment atmosphere as mentioned above. We have concluded that the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys is an extrinsic nature, i.e., a kind of artifact during the heat treatment..
131. Mitsuhiro Matsuda, Yoshihito Kawamura, Minoru Nishida, Production of high strength Mg97Zn1Y2 alloy by using mechanically alloyed MgH2 powder, Materials Transactions, 10.2320/matertrans.44.440, 44, 4, 440-444, 2003.01, The Mg97Zn1Y2 bulk alloy has been produced by MA-HDH P/M process using MgH2 powders as the starting material. As-extruded Mg97Zn1Y2 bulk alloy of MAed powders showed a high compressive yield strength of 616 MPa and a plastic strain of 4.2%. These values were much higher than those of commercial ingot metallurgy (I/M) Mg alloys, such as AZ91 and ZK60. This is originated from the refinement of hcp-Mg grains, the solid solution hardening of Zn and Y, and the dispersion hardening by MgO and Y2O3 fine particles. No degradation was observed in mechanical properties of the alloy even after annealing at 673 K for prolonging time. This is considered to be due to the inhibition of the hcp-Mg grain growth by the densely dispersed MgO and Y2O3 fine particles. Therefore, MA-HDH P/M Mg97Zn1 Y2 alloy is promising as the structural material for high temperature applications..
132. Yasuhiro Morizono, Ryohei Kumagae, Minoru Nishida, Yoshiyuki Mizuta, Akira Chiba, Superplasticity-like behavior of rapidly solidified Ti-rich TiAl powders and its application to in-situ sintering bonding, Materials Transactions, 10.2320/matertrans.44.754, 44, 4, 754-758, 2003.01, The application of rapidly solidified Ti-rich TiAl alloy powders to bonding technique has been proposed. The alloy powders are produced by plasma rotating electrode process (PREP), Among them, the powders (denoted as M powders) having surface relief of martensitic phase are used as an interlayer of the joint. The bonding of two Ti-50 mol% Al alloy disks was performed at 1273 K for 0.6 ks under 1.9 kN using the M powders of Ti-40 mol% Al alloy. Since the M powder shows superplasticity-like deformation, there are no defects such as void and oxide film in the bonding interface and the powders in the interlayer are indistinguishable. It is also confirmed that the bonding strength of the obtained joint increases notably by the use of the powder interlayer. Consequently, the bonding of the TiAl disks is achieved well by the excellent deformation behavior of the M powder even at relatively lower temperature and shorter holding time..
133. Mitsuhiro Matsuda, Shintaro Yoshimoto, Yoshihito Kawamura, Kazuhiro Ishikawa, Minoru Nishida, Development of high strength Mg alloys by MA-HDH P/M process, Materials Science Forum, 419-422, II, 739-744, 2003, MA-HDH P/M process for the production of Mg bulk alloy has been established by using MgH2 powders as the starting material. The as-extruded Mg95Zn2.5Zr2.5 bulk alloy of MAed powders showed high compressive yield strength of 613 MPa, which was originated from the refinement of hcp-Mg grains, the solid solution hardening of Zn and Zr, and the precipitation hardening by MgO fine particles. The compressive yield strength of the MA-HDH P/M Mg95Zn2.5Zr2.5 alloy annealed at 823K for 10.8 ks was as high as that of the as-extruded Mg95Zn2.5Zr2.5 bulk alloy. This seems to be due to the suppression of the hcp-Mg grain growth by the densely dispersed MgO fine particles..
134. S. Ii, Minoru Nishida, T. Hara, Crystallography and morphology of twins in 9R martensite in Ti-Pd-Fe shape memory alloy, Scripta Materialia, 10.1016/S1359-6462(01)01238-6, 46, 7, 549-554, 2002.04, Twins in 9R martensite in Ti50.0Pd43.0Fe7.0 shape memory alloy are investigated by conventional transmission electron microscopy. There are four twinning modes, i.e., {114}9R Type I, 〈591〉9R Type II, {105}9R compound and {001}9R compound twins. The {114}9R Type I and the 〈591〉9R Type II twins are considered to be lattice invariant shear in the 9R martensite continuously coexisting with 2H martensite. On the other hand, those two twins and {105}9R compound twin can be regarded as variant accommodation twins in the region only consisting of the 9R martensite. Irrational nature of Type II twin boundary, i.e., A:B type pair, is also observed in the edge-on state by high resolution electron microscopy (HREM). The boundary is gradually and randomly curved with strain contrast..
135. Sei Ichiro Ii, Minoru Nishida, Toru Hara, Kazuyuki Enami, Combination and interface structure of 9R martensite plate variants in Ti50.0Pd43.0Fe7.0 shape memory alloy, Materials Transactions, 10.2320/matertrans.43.902, 43, 5, 902-907, 2002.01, The combination of 9R martensite plate variants in Ti50.0Pd43.0Fe7.0 shape memory alloy has been investigated by conventional transmission electron microscopy (CTEM). Three fundamental combinations of plate variants are identified in the plate group. These are designated as A:B, A:C and A:D types, which correspond to 〈5̄91〉9R Type II, {114̄}9R Type I and {105}9R compound twins, respectively. They show the same morphological characteristics of 9R and 18R martensite in Cu-base shape memory alloys, i.e., wedge, spear and fork (or kink) types. The Type II and compound twins are new findings. Irrational nature of the A:B interface is also studied in the edge-on state by high resolution electron microscopy (HREM). The boundary is gradually and randomly curved with strain contrast..
136. Y. Morizono, Minoru Nishida, A. Chiba, Effect of Zr and Ta inserts on bonding strength and interracial microstructures of Ti/steel clads, ISIJ International, 10.2355/isijinternational.42.645, 42, 6, 645-650, 2002.01, Bonding strength and interfacial microstructures of Ti/steel clads using Zr and Ta inserts have been investigated from the viewpoint of diffusion barrier effect of carbide laver formed at the interface. Diffusion bonding was performed at 1 073 to 1 273 K for 3.6 and 14.4 ks in a vacuum. TiC layer, as a diffusion barrier, is observed at the interface in the Ti/low carbon steel (structural steel, SS400) clad bonded at 1 073 K and 1 173 K without Zr and Ta inserts. However, the clad bonded at 1 273 K has no TiC barrier layer, and thus microstructural change resulting from the diffusion of Fe and Ti atoms into each parent material is observed. Although Zr insert is used in order to produce the carbide layer showing diffusion barrier effect at 1 273 K, such a layer cannot be obtained because of eutectic reaction between the steel and the insert. On the other hand, Ta insert leads to the formation of reaction layer consisting of TaC and Ta2C in the clad bonded at 1 273 K. This clad shows the highest bonding strength in the present study. Therefore, Ta insert makes it possible to retain diffusion barrier effect of carbide layer at the temperature of 1 273 K and improves the bonding strength of the Ti/SS400 steel clad as well. The advantages of Zr and Ta inserts for Ti/high carbon steel and Ti/stainless steel clads are also discussed..
137. Virgil Constantin Solomon, Minoru Nishida, Effect of aging on martensitic transformation in Ti-Rich Ti-Pd shape memory alloy, Materials Transactions, 10.2320/matertrans.43.897, 43, 5, 897-901, 2002.01, Effect of aging on successive martensitic transformation in a Ti-47 at%Pd shape memory alloy has been studied by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). After short time aging successive transformation takes place in Ti-47 at%Pd alloy irrespective of aging temperature. On the other hand, after relatively prolonged period only the specimen aged above 1073 K shows successive transformation. The change of transformation behavior with aging condition is discussed on the basis of equilibrium between TiPd matrix and Ti2Pd precipitate. The homogeneity range of TiPd compound is also estimated from the transformation behavior and TEM observations..
138. Virgil Constantin Solomon, Minoru Nishida, Martensitic transformation in Ti-rich Ti-Pd shape memory alloys, Materials Transactions, 10.2320/matertrans.43.908, 43, 5, 908-915, 2002.01, A systematic study on martensitic transformation in Ti-rich Ti-Pd alloys has been carried out using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The alloys quenched from the single region of B2 parent phase show a successive transformation during DSC measurement. On the other hand, the furnace-cooled alloys show a single transformation. The successive transformation behavior is closely related to the formation of fine Ti2Pd precipitates with C11b-type structure during transformation cycle. The first peak on DSC heating curve is attributable to the reverse martensitic transformation of the TiPd matrix, while the second one is due to the reverse martensitic transformation in local regions around the Ti2Pd precipitates where Pd concentration is higher than that in matrix. Morphological characteristics of the precipitate are also discussed..
139. K. Noguchi, Minoru Nishida, A. Chiba, Transmission electron microscopy of NiCrAlY raw powder material and the low pressure plasma sprayed coating, Scripta Materialia, 10.1016/S1359-6462(00)00609-6, 44, 3, 467-473, 2001.03, The microstructure of low pressure plasma sprayed (LPPS) CoNiCrAlY coating is investigated by TEM to show that the characterization is effective for examining the spray mechanism. Microstructural characterizations by TEM and micro Vickers hardness test are carried out on the NiCrAlY raw powder material and the LPPS coating. The microstructure and the mechanical properties of the raw powder material are compared with those of the coating in the investigation of spray mechanism..
140. Yasumichi Matsumoto, Yoshie Ishikawa, Minoru Nishida, Seiichiro Ii, A New Electrochemical Method to Prepare Mesoporous Titanium(IV) Oxide Photocatalyst Fixed on Alumite Substrate, Journal of Physical Chemistry B, 104, 17, 4204-4209, 2000.05, A TiO2 film was deposited onto alumite using an electrochemical technique, where the initial electrodeposition was carried out by ac electrolysis in (NH4)2[TiO(C2O4)2] solution, followed by pulse electrolysis in TiCl3. This is a new method to prepare a mesoporous TiO2 photocatalyst film consisting of nanosized particles and to directly fix them onto the alumite substrate (Al/Al2O3). The sizes of the TiO2 particles in the prepared film were about 5 nm, and they consisted of mixtures of the anatase, rutile, and amorphous phases. This film had a high catalytic activity for the decomposition of acetaldehyde even under fluorescent lamp illumination. Moreover, the preparation cost is very low compared with other methods. Therefore, the prepared Al/Al2O3/ TiO2 plate is very useful for the practical photodecomposition of chemical contaminants in the atmosphere. The mechanisms of the TiO2 deposition and the photocatalysis are discussed..
141. Minoru Nishida, S. Ii, Crystallography and boundary structure of twins in Ti-Ni and Ti-Pd martensites, Unknown Journal, 327, 103-110, 2000, Morphology and crystallography of twins in the martensite in Ti-Ni and Ti-Pd shape memory alloys are reviewed on the basis of recent electron microscopy observations. It has been confirmed that there are five and three twinning modes in Ti-Ni and Ti-Pd martensites, respectively. The morphology and crystallography of newly found deformation twin in Ti-Ni martensite are briefly reported. The irrational nature of Type II twin boundary has been clarified by high resolution electron microscopy observations in edge-on state. There are neither ledge nor step structures at the irrational boundary..
142. G. Oomi, S. Aduma, I. Kosaka, T. Kagayama, Minoru Nishida, Design of a new high pressure apparatus using shape memory alloy, Unknown Journal, 327, 39-42, 2000, A new high pressure apparatus using Ti-Ni shape memory alloy as an actuator has been developed. It is found that the high pressure around 10 GPa is easily obtained when we use the Bridgman type anvil having a face of 3 mm in diameter. Some other properties of this high pressure apparatus are reported briefly..
143. S. Ii, N. Matsuzaki, Y. Morizono, Minoru Nishida, Effect of thermal cycling and aging on microstructure in near-equiatomic Ti-Pd alloys, Unknown Journal, 327, 167-170, 2000, The effect of thermal cycling and aging on the transformation behaviors and the microstructure in martensite of Ti-50.0 at%Pd alloy has been investigated by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). There is no change in Af temperature upon thermal cycling in spite of the increase of volume fraction of {101} compound twinning and the dislocation density. The aging treatment was subjected just below the As temperature. Af temperature of the aged alloys slightly increases with increasing aging period. Twinning modes in martensite in the aged specimen are essentially the same as those of the solution treated one. However, a large number of stacking faults on the (001)B19 basal plane is induced upon aging..
144. Y. Shirakawa, Y. Morizono, Minoru Nishida, New precipitate phase in Pd and Ni rich Ti-Pd-Ni shape memory alloys, Unknown Journal, 327, 171-174, 2000, The decomposition behavior and morphology of new precipitate in Pd and Ni rich Ti-Pd-Ni high temperature shape memory alloys have been studied by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The precipitate is formed in Ti48Pd52-XNiX alloys with X = 11 to 36 at%Ni. The precipitate appears with exothermic peak about 650 to 700 K and resolves with endothermic peak with about 740 to 780 K in DSC heating curve for the quenched alloys. The both peak temperatures increase with increasing Ni concentration. The shape of precipitate changes from cuboid to oval sphere shapes with increasing Ni concentration. The electron diffraction patterns of the precipitate are characterized by 1/4{111} superlattice reflections in B2 reciprocal space. The Ti48Pd31Ni21 alloy aged under constrained condition at 673 K for 36 ks shows reversible shape memory effect during thermal cycling between room temperature and 523 K..
145. Y. Maruhashi, A. Ozaygen, Minoru Nishida, Relation between {201̄} twinning of B19′ martensitic and {114} twinning of B2 parent phases in Ti-Ni shape memory alloy, Unknown Journal, 327, 163-166, 2000, A direct evidence of the relation between {201̄}B19′ twinning in the deformed martensite and {114}B2 twinning in the TiNi alloys' parent phase after reverse transformation is demonstrated by conventional and high resolution electron microscopies. There is the continuity of K1 planes between the two twinnings. Such that the {201̄}B19′ twinning is retained after the {4̄11}B2 twinning as a complement of reverse transformation. The validity of the results is based on the orientation relationship between martensite and parent phases and the magnitude of twinning shear for both the twinnings..
146. Yasuhiro Morizono, Minoru Nishida, Akira Chiba, Kihachirou Imamura, Effect of heat treatment on bonding characteristics and interfacial microstructures in explosively welded Ti/SUS430 stainless steel clad, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.85.4_340, 85, 4, 340-345, 1999.01, Effect of heat treatment on bonding characteristics and interfacial microstructures in explosively welded titanium/SUS430 ferritic stainless steel clad was investigated. The average shear strength of the clad annealed at 1073K for 3.6 ks was 338 MPa and was equivalent to about 60% of that of an as-welded clad. The strength of the clad annealed at 1073K gradually decreased to 242 MPa with increasing holding time up to 360ks. The same tendency was obtained from the clad annealed at 1173K. On the other hand, the strength of the clad annealed at 1273K drastically decreased to 107 MPa with increasing holding time up to 360ks. The clad annealed at 1073 and 1173K yielded TiC layer at the bonding interface, while the reaction layer in the clad annealed 1273K consisted of TiC, FeTi, Fe2Ti and χ (Fe29Cr13Ti8) from titanium side. It was noted that chromium existed in the Fe2Ti, which has wide solubility limit for chromium, and χ compounds formed at the SUS430 side. The TiC layer in the former clads acts as a barrier for diffusion of titanium, iron and chromium across the bonding interface and prevents the growth of intermetallic compounds. The clad formed TiC layer at the bonding interface preserved high bonding strength even after prolonged annealing..
147. Takashi Sakamoto, Minoru Nishida, Kenji Okazaki, Microstructure of Mo powders sintered with Ni and Ni3Al powders, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.46.1221, 46, 12, 1221-1225, 1999.01, When Ni or Ni3Al powders are added to Mo powders, sintering is greatly promoted to result in significantly higher densities even at lower temperatures than one-half of the homologous temperature for Mo. The activation energies obtained for mixed sintering are lower than that required for mutual volume diffusion between Mo and Ni. TEM observations of microstructure after sintering Mo and Ni powders at 1573 K revealed the formation of a MoNi phase at interfaces of Mo particles. When sintered at 1673 K, not only Mo-Ni phase is seen at the interface but also the Mo particle surface became slightly wavy as a result of contacting with the liquid Mo-Ni phase. When Mo powders were sintered with a 5 wt.% of Ni3Al alloy powders at 1573 K, the microstructure obtained by quenching from this temperature is a mixture of Mo and Ni3Al. But the microstructure obtained by furnace-cooling is a mixture of Mo, Mo-Ni and Ni3Al which is surrounded by MoNi3..
148. Taizo Sato, Yuji Tashiro, Yoshitaka Honda, Minoru Nishida, Akira Chiba, The Influence of Cold Rolling Reduction on r-value and Recrystallization Behavior in Fe-36Ni Alloy, ISIJ International, 38, 6, 640-646, 1998.12, Recrystallization behavior and grain growth in Fe-36%Ni invar alloy for shadow masks in color cathode ray tubes are studied by using transmission electron microscopy. The r-value increases with increasing (111) surface intensity. In case of light cold-rolling reduction, nuclei orientations of recrystallized structure after annealing are (011) and the nuclei are surrounded by cold rolled matrices of (011) orientation. On the other hand, in case of heavy cold rolling reduction, nuclei orientations of recrystallized structure after annealing are (011) and (100). These two nuclei are surrounded by the same cold rolled matrices of (011) orientation with light cold rolling reduction..
149. Minoru Nishida, S. Ii, K. Kitamura, T. Furukawa, A. Chiba, T. Hara, K. Hiraga, New deformation twinning mode of B19′ martensite in Ti-Ni shape memory alloy, Scripta Materialia, 10.1016/S1359-6462(98)00366-2, 39, 12, 1749-1754, 1998.11.
150. M. Hayakawa, H. Miyauchi, A. Ikegami, Minoru Nishida, Elastic constants of zirconia single crystals determined by X-ray measurements for polycrystals, materials transactions, jim, 10.2320/matertrans1989.39.268, 39, 2, 268-274, 1998.01, A previously developed method for determining elastic constants of single crystals from polycrystalline specimens was applied to cubic and tetragonal zirconia. The method is based on the orientation dependence of the lattice strain of a stressed specimen as measured by X-ray diffraction and also on Kröner's equation relating the elastic constants of polycrystals to those of a single crystal. A simple loading device for a disc-shaped specimen was developed using a Ti-Ni shape memory alloy. The resulting elastic constants, C11, C12, and C44 for cubic zirconia were in fair agreement with those measured directly on a single crystal. The same method was applied to tetragonal zirconia after verifying that the elasticity of this material may be well approximated by cubic symmetry. Error analysis and suggestions for an improved measurement are also included..
151. Minoru Nishida, Y. Morizono, T. Kai, J. Sugimoto, A. Chiba, Grain refining and superplastic compaction of rapidly solidified TiAl powder with phase separation of nonequilibrium α2 martensite, Materials Science Forum, 233-234, 303-310, 1997.12, There were two kinds of powders with respect to microstructures in the rapidly solidified Ti-rich TiAl powders produced by Plasma Rotating Electrode Process (PREP). The first one had a surface relief of a martensitic phase and consisted of α2 lath plates and the primary phase during solidification was deduced to be the β phase, which is referred as M powder. The second one had a dendritic structure and consisted of α2/γ lamellar and γ phases decomposed in the α2 matrix, which is referred as D powder. The primary phase of the D powder during solidification was determined to be the α phase. In Ti-40 at%Al alloy, α2/γ lamellar and α2/γ microduplex structures were formed in D and M powders, respectively, by annealing at 1273 K. The microduplex structure consisted of γ precipitate in α2 matrix with the usual orientation relationship. The D powder was difficult to compact by hot press at 1273 K at 50 MPa. Lots of dislocations were observed in the lamellar structure. The M powder was compacted easily by hot press at 1273 K at 50 MPa. α2 and γ phases in the duplex structure were lost the usual orientation relationship during the hot press. There were no dislocations inside of α2 and γ crystal grains. It was concluded that the grain boundary sliding was a predominant deformation mode in the M powder during the hot press. In other words, the M powder exhibited a superplastic deformation behavior at elevated temperature. D and M powders in Ti-45 and 47 at%Al alloys showed the same tendency as those in Ti-40 at%Al alloy..
152. T. Mashimo, S. Tashiro, Minoru Nishida, K. Miyahara, E. Eto, B1-type and WC-type phase bulk bodies of tantalum nitride prepared by shock and static compressions, Physica B: Condensed Matter, 10.1016/S0921-4526(97)00367-0, 239, 1-2, 13-15, 1997.08, Tantalum nitride (TaN) is a unique nitride which has CoSn-type structure at ambient state among the transition metal nitrides (1:1). We have been performing the shock-and static-high-pressure compression experiments to synthesize the dense-phase tantalum nitrides. The single-phase bulk body of B1-type tantalum nitride with good stoichiornetry was prepared by shock compression. The single-phase bulk bodies of B1-and WC-type tantalum nitrides were also prepared by static compression. The static-compression quenching experiments showed that the B1-type phase was a high-temperature high-pressure phase and the WC-type phase was a low-temperature high-pressure phase. The B1-and WC-type phases bulk bodies had good high-temperature stabilities and much higher hardnesses than the CoSn-type. The shock-compression-synthesized B1-type one showed superconductivity with a comparatively high critical temperature..
153. Y. Morizono, Minoru Nishida, A. Chiba, Diffusion barrier effect of carbide layer on bonding characteristics of Ti/steel clad, Proceedings of the 1996 MRS Fall Meeting Materials Research Society Symposium - Proceedings, 458, 363-368, 1997.01, Bonding characteristics and interfacial microstructures in explosively welded Ti/stainless steel clad of the as-welded and annealed states were investigated. In case of Ti/SUS430 ferritic stainless steel combination, the average shear strength of an as-welded clad was 555 MPa, and metastable phases such as amorphous and fine crystalline phases were observed at the interface. These were considered to the trace of melting and subsequently rapid solidification at the contact surface of both the parent materials. By annealing below 1173 K, the strength gradually decreased with increasing holding time. The average shear strength of the clad annealed at 1073 K for 360 ks was 242 MPa, while that of the clad annealed at 1273 K abruptly decreased down to 107 MPa with increasing holding time up to 360 ks. The reaction layer formed at the interface consisted only of TiC in the former. On the other hand, the coexistence of TiC, TiFe, TiFe2 and χ was observed at the interface in the latter. The TiC in the former was considered to serve as a barrier for diffusion of Ti, Fe and Cr across the interface and to suppress the formation of intermetallic compounds. As a result, the growth of reaction layer was inhibited and high bonding strength was preserved even after prolonged annealing. The results of the combination of Ti and SUS304 austenitic stainless steel were also discussed..
154. Akira Chiba, Minoru Nishida, Yasuhiro Morizono, Kihatioru Imamura, Diffusion barrier effect of TiC layer formed at the bonding interface and bonding characteristics of an explosively welded Ti/SUS420J1 stainless steel clad by heat treatment, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.83.11_736, 83, 11, 1997.01, The high temperature stability of an explosively welded Ti/SUS420J1 stainless steel clad was assessed by studying microstructures and bonding strengths of the clads with changing the annealing temperature. Compounds formed at their bonding interfaces consisted of TiC , FeTi, and/or Fe2Ti phases depending on the annealing conditions. The TiC layer formed at the boundary acts as an barrier for the diffusion of the base metals across the bonding interface under the 1000°C annealing and prevents the growth of intermetallic compounds, (FeTi and Fe2Ti) and of β-Ti. The specimens formed TiC layer at the bonding interface sustained high bonding strength even by high temperature annealing. Diffusion barrier effect diminished above 1050°C annealing due to the dissolution of TiC layer in γ matrix and the strength decreased. The diffusion barrier effect of the TiC layer was discussed on the basis of phase diagrams and physical properties of TiC compound..
155. Minoru Nishida, Yasuhiro Morizono, Tomoaki Kai, Jim Sugimoto, Akira Chiba, Ryohei Kumagae, Microstructure dependence of compactibility of rapidly solidified Ti-rich TiAl alloy powders produced by plasma rotating electrode process, Materials Transactions, JIM, 10.2320/matertrans1989.38.334, 38, 4, 334-343, 1997.01, The effect of initial microstructure on the compactibility at elevated temperatures in rapidly solidified Ti-rich TiAl alloy powders produced by the plasma rotating electrode process (PREP) has been investigated. There are two kinds of powders with respect to the microstructure. The first one has a surface relief of a martensitic phase and consists of twin-related α2(Ti3Al) lath platelets, which is referred to as M powder. The second one has a dendritic structure and consists of a single phase of α2 with no microstructure other than the grain boundary, which is referred to as D powder, α2+γ (TiAl) microduplex and α2/γ lamellar structures are formed in M and D powders of the Ti-40 at%Al alloy by heat treatment at 1273 K, respectively. The microduplex structure consists of γ precipitate in the twin-related α2 matrix with the usual orientation relationship. It is difficult to compact the D powder by hot pressing at 1273 K under 50 MPa for 14.4 ks. On the other hand, the M powder is compacted easily by hot pressing with the same condition. The twin-related α2 and α2 boundary changes to random ones and the α2 and γ phases lose the usual orientation relationship in the duplex structure during the hot pressing. In other words, the low energy boundaries are changed to the high energy ones suitable for grain boundary sliding. Dislocations are scarcely observed inside of both the α2 and γ crystal grains. It is concluded that the grain boundary sliding is a predominant deformation mode in the M powder during the hot pressing. The D and M powders in Ti-45 and 47 at%Al alloys show the same tendency as those in Ti-40 at%Al alloy during hot pressing. From the practical viewpoint the optimization of PREP conditions is also discussed to increase the number fraction of the M powder..
156. Toru Hara, Takuya Ohba, Kazuhiro Otsuka, Minoru Nishida, Phase transformation and crystal structures of Ti2Ni3 precipitates in Ti-Ni alloys, Materials Transactions, JIM, 10.2320/matertrans1989.38.277, 38, 4, 277-284, 1997.01, In Ni-rich Ti-Ni alloys, three kinds of precipitates such as TiNi3, Ti2Ni3 and Ti3Ni4 appear with aging heat-treatments. The shape memory effect and superelasticity of the alloys are greatly affected by the presence of these precipitates. It is interesting to note that the Ti2Ni3 precipitate itself exhibits a phase transformation. However, the characteristics of this transformation is not understood in detail as yet. In the present study, the characteristics of this transformation were studied from crystallographic point of view. The crystal structures of the low- and the high-temperature phases were determined by combining several techniques such as electron diffraction, convergent beam electron diffraction, high resolution electron microscopy and powder X-ray diffraction with the Rietveld analysis. The results of these analyses revealed that the space group of the low- and the high-temperature phases are Bbmm and I 4/mmm, respectively. It was reported that the Ti2(Ni, Cu)3 alloy shows a similar transformation. The relevance of the transformation in this alloy to Ti2Ni3 precipitates is also discussed..
157. Minoru Nishida, T. Hara, Y. Morizono, A. Ikeya, H. Kijima, A. Chiba, Transmission electron microscopy of twins in martensite in Ti-Pd shape memory alloy, Acta Materialia, 10.1016/S1359-6454(97)00162-6, 45, 11, 4847-4853, 1997.01, Twins in the B19 martensite in the Ti-Pd shape memory alloy have been investigated by conventional transmission electron microscopy (CTEM) and electron diffraction. There were three twinning modes, i.e. {111} Type I, 〈121〉 Type II and {101} compound twins, in the martensite. The {111} Type I and 〈121〉 Type II twinnings which were conjugate to each other coexisted in a same martensite variant. The {111} Type I twins were dominantly observed and the 〈121〉 Type II twins were less frequently observed. The former twinning was considered to be a lattice invariant shear. The Type II twin plate appeared in two types of forms. The first one was directly connected to the Type I plate. In other words, the twin plate was inclined at crystallographically defined angle. The second one branched off from the Type I plate. Since there was no martensite variant consisting wholly of the 〈121〉 Type II twins throughout the present observations, the 〈121〉 Type II twins were considered to be a deformation twin due to the elastic interaction during the transformation. The {101} compound twinning was also considered to be a deformation twin which was introduced as result of elastic interactions during the transformation since the twin had an isolated fashion in the martensite variant consisting of {111} Type I twins..
158. Minoru Nishida, A. Chiba, Y. Morizono, T. Kai, J. Sugimoto, Effect of initial microstructure on the compactibility of rapidly solidified Ti-rich TiAl powder, Unknown Journal, 460, 45-50, 1997, Initial microstructure dependence of compactibility at elevated temperature in rapidly solidified Ti-rich TiAl alloy powders produced by plasma rotating electrode process (PREP) has been investigated. There were two kinds of powders with respect to the microstructure. The first one had a surface relief of a martensitic phase, which was referred as M powder. The second one had a dendritic structure, which was referred as D powder. α2+γ microduplex and α2/γ lamellar structures were formed in M and D powders of the Ti-40 at%Al alloy by heat treatment at 1273 K, respectively. The microduplex structure consisted of γ precipitate in the twin related α2 matrix with the usual orientation relationship. It was difficult to compact the D powder by hot pressing at 1273 K under 50 MPa for 14.4 ks. On the other hand, the M powder was compacted easily by hot pressing with the same condition. The twin related α2 and α2 boundary changed to random ones and the α2 and γ phases were lost the usual orientation relationship in the duplex structure during the hot pressing. In other words, the low energy boundaries were changed to the high energy ones suitable for grain boundary sliding. Dislocations were scarcely observed inside of both the α2 and γ crystal grains. It was concluded that the grain boundary sliding was a predominant deformation mode in the M powder during the hot pressing. D and M powders in Ti-45 and 47 at%Al alloys showed the same tendency as those in Ti-40 at%Al alloy during hot pressing..
159. Minoru Nishida, Y. Morizono, H. Kijima, A. Ikeya, H. Iwashita, K. Hiraga, Phase transformations and crystallography of twins in martensite in Ti-Pd alloys, Materials Research Society Symposium - Proceedings, 459, 375-380, 1997, Phase transformations and crystallography of twins in near-equiatomic Ti-Pd alloys have been studied. In the first half we have found that the transformation temperature decreases with decreasing the Pd contents and the successive transformations take place in the Ti-rich alloys. While the transformation temperature is nearly constant with the composition and a single transformation takes place in the equiatomic and Pd-rich alloys. The solubility limit of TiPd compound in Ti-rich side is extended to about 55 at%Ti at 900 °C and abruptly decreased with decreasing temperature. In the latter half we have found three twinning modes, i.e., {111} Type I, 〈121〉 Type II and {101} compound twins, in the martensite. The {111} Type I and 〈121〉 Type II twinnings which are conjugate to each other coexist in the same variant. The {111} Type I twins are dominantly observed and the 〈121〉 Type II twins are less frequently observed. The former twinning is considered to be a lattice invariant shear. There is no martensite variant consisting wholly of the 〈121〉 Type II twins throughout the present observation. The 〈121〉 Type II twinning is considered to be a deformation twin due to the elastic interaction during the transformation. The {101} compound twinning is also considered to be a deformation twin, since the twin has an isolated fashion in the martensite variant. The boundary structure of the above three twinning modes was also discussed on the basis of lattice image..
160. K. Noguchi, Minoru Nishida, A. Chiba, Transmission electron microscopy of low pressure plasma sprayed CoNiCrAlY coating, Scripta Materialia, 10.1016/1359-6462(96)00304-1, 35, 11, 1359-1364, 1996.12.
161. K. Yamauchi, Minoru Nishida, I. Itai, K. Kitamura A Chiba, Specimen preparation for transmission electron microscopy of twins in B19 martensite of Ti-Ni shape memory alloys, Materials Transactions, JIM, 10.2320/matertrans1989.37.210, 37, 3, 210-217, 1996.01, Specimen preparation for transmission electron microscopy (TEM) of twins in B19′ martensite in the edge-on state of polycrystalline Ti-Ni shape memory alloys was proposed utilizing the recrystallization texture of cold-drawn rod and the parent-martensite lattice correspondences. The five twinning modes, i.e. <011>Type II, {11I} Type I, {011} Type I, (100) compound and (001) compound twins, were observed in the martensite. The <011> of the martensite which is derived from the <001> of the parent phase is in the edge-on state for all the observed twinning modes, except for the (001) compound twinning. The <100> of the martensite which also corresponds to the <001> of the parent phase is in the edge-on state for the {011} Type I and (001) compound twinnings. There was the <111> recrystallization fiber texture of the parent phase in the cold-drawn and subsequently annealed rod. Therefore, the identification of twinning modes by electron diffraction and the high resolution electron microscopy (HREM) study of twin boundaries in the edge-on state were easily performed using the specimen which was sliced obliquely about 50 degrees to the drawing axis of the rod..
162. Tsutomu Mashimo, Akira Nakamura, Minoru Nishida, Susumu Matsuzaki, Keiji Kusaba, Kiyoto Fukuoka, Yasuhiko Syono, Anomalous shock compression behavior of yttria-doped tetragonal zirconia, Journal of Applied Physics, 10.1063/1.359315, 77, 10, 5069-5076, 1995.12, Shock-wave measurement and shock-compression recovery experiments of yttria (Y2O3) -doped (3.0 mol %) tetragonal zirconia in the pressure range up to 125 GPa were performed to study the anomalous shock compression and release behaviors. The minute three-wave structure with the transition points of 15-17 and 33-35 GPa was observed also by the inclined-mirror method, which is consistent with the VISAR (velocity interferometer system for any reflector) data. The shock velocities of the second wave were so fast that the first transition could not be identified as a normal elastoplastic transition. The shock velocity Us versus particle velocity Up relation of the final wave was given by U s=2.71+2.39Up km/s. The equation of state of the final phase was analyzed by using a program based on the Debye model, the Mie-Grüneisen equation, and the Birch-Marnaghan equation. The volume change between the tetragonal phase and the final phase at zero pressure was estimated to be 18%, which was larger than that expected for the tetragonal-orthorhombic II transition. The bulk moduli of the final phase at zero pressure was estimated to be 550 GPa. An instability was observed at release in the stress history of 28 GPa in peak stress. A certain amount of the monoclinic phase was observed at fractured surfaces of the recovered specimens from the shock compressions of below and above the first transition point (15-17 GPa) by Raman spectrum and transmission electron microscope observations. This might be related to the observed anomalous shock compression and release behaviors..
163. A. Chiba, Minoru Nishida, Y. Morizono, K. Imamura, Bonding characteristics and diffusion barrier effect of the TiC phase formed at the bonding interface in an explosively welded titanium/high- carbon steel clad, Journal of Phase Equilibria, 10.1007/BF02645348, 16, 5, 411-415, 1995.10, Microstructural aspects and bonding characteristics of the explosively welded titanium/high-carbon steel clad of the as-welded and postannealed states were investigated. Amorphous and βTi phases were observed at the interface in the as-welded clad. These were considered to be the trace of melting and subsequently rapid solidification of thin layers along the contact surface of both the parent materials. The melting layer was considered to be responsible for the substantial bonding. The TiC layer was formed at the bonding interface by postannealing, which served as a barrier for diffusion of species across the interface and suppressed the formation of Fe-Ti intermetallic compounds. As a result, high bonding strength was preserved even after prolonged annealing at elevated temperatures..
164. Yasuhiro Morizono, Takashi Nakata, Minoru Nishida, Akira Chiba, Effect of active metal on bonding characteristics and interfacial structure of the Si3N4/Si3N4 joints brazed by Ag-Cu filler metal, Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan, 10.2109/jcersj.103.810, 103, 1200, 810-815, 1995.01, Joining of Si3N4 to Si3N4 was carried out using Ag-Cu filler metal containing Ti, Zr, V and Nb as an active metal. Bonding treatment was performed at 1173 to 1473 K for 1h in a vacuum. The shear strengths of the joints brazed at 1173 to 1473 K using active filler metals containing Ti and Zr were 150 to 250 MPa. The fracture position of the joints after shear test was the filler metal or mixture of the filler metal and Si3N4. On the other hand, the average shear strengths of the joints brazed at 1373 K using active filler metals containing V and Nb were 144 and 163 MPa, respectively. The fracture position of the joints using these filler metals was the interface between filler metal and Si3N4 in all cases. The active filler metals containing Ti and Zr yielded TiN and ZrN fine grains close to the Si3N4. No fine grains were observed in the joint using active filler metal containing V and coarse columnar grains of V3Si were observed. Therefore, it is concluded that the fine grains of the nitrides formed close to the Si3N4 is responsible for the substantial bonding between filler metal and Si3N4..
165. Minoru Nishida, Akira Chiba, Yositaka Honda, Jun ichi Hirazumi, Koji Horikiri, Electron Microscopy Studies of Bonding Interface in Explosively Welded Ti/Steel Clads, isij international, 10.2355/isijinternational.35.217, 35, 2, 217-219, 1995.01, Microstructural modifications of bonding interface in explosively welded Ti/SUS 304 and Ti/SS 41 steels clads were studied by transmission electron microscopy. Metastable phases such as amorphous and supersaturated solid solution of β-Ti were observed at the interface. These were considered to be the trace of melting and subsequently rapid solidification of thin layers along the contact surface of both the parent materials. It is concluded that the melting layer is responsible for the bonding of explosively welded Ti/steel clads..
166. Minoru Nishida, H. Ohgi, I. Itai, A. Chiba, K. Yamauchi, Electron microscopy studies of twin morphologies in B19′ martensite in the Ti-Ni shape memory alloy, Acta Metallurgica Et Materialia, 10.1016/0956-7151(94)00332-C, 43, 3, 1219-1227, 1995.01, Twins in the B19′ martensite in the Ti-Ni shape memory alloy have been investigated by conventional transmission electron microscopy (CTEM) and electron diffraction. The following five twinning modes were observed. The 〈011〉 Type II twin was dominantly observed among those and confirmed to be a lattice invariant shear since most martensite variants consisted of the 〈011〉 Type II twinning. The {111-} Type I twinning was morphologically and characteristically divided into three types, i.e. a deformation twin, a variant accommodation twin and a lattice invariant shear. (100) and (001) compound twinnings were considered to be a deformation twin. The 011 Type I twinning was inevitably reconfirmed and considered to be a lattice invariant shear rather than a deformation twin since it extended over the whole martensite plate. The formation order and mechanism of each twinning mode were qualitatively discussed in view of the elastic interaction accumulated during the martensitic transformation..
167. K. Hokamoto, A. Chiba, Minoru Nishida, M. Fujita, Experimental conditions for fabrication of multilayered metal base composites by single‐shot explosive welding, Welding International, 10.1080/09507119509548765, 9, 2, 116-120, 1995.01.
168. Minoru Nishida, Akira Chiba, Yasuhiro Morizono, Mitsuhiro Matsumoto, Takanobu Murakami, Akihisa Inoue, Formation of nonequilibrium phases at collision interface in an explosively welded Ti/Ni clad, Materials Transactions, JIM, 10.2320/matertrans1989.36.1338, 36, 11, 1338-1343, 1995.01, Microstructural modifications of collision interface in an explosively welded Ti/Ni clad were studied by transmission electron microscopy. Nonequilibrium phases such as amorphous and icosahedral quasicrystalline phases were synthesized and locked into the collision interface. These products were concluded to be the trace of melting and subsequently rapid solidification of thin layers along the contact surface of both the parent materials. It was considered that the impact pressure during explosive welding promoted the formation of the nonequilibrium phases. The solidification process of the molten layer was also discussed..
169. Minoru Nishida, K. Yamauchi, I. Itai, H. Ohgi, A. Chiba, High resolution electron microscopy studies of twin boundary structures in B19′ martensite in the Ti-Ni shape memory alloy, Acta Metallurgica et Materialia, 10.1016/0956-7151(94)00328-F, 43, 3, 1229-1234, 1995.01, The boundary structure of the 〈011〉 Type II, {111-} Type I, 011 Type I, (100) compound and (001) compound twins in the B19′ martensite in the Ti-Ni shape memory alloy was observed in the edge-on state by high resolution electron microscopy (HREM). The lattice images of the Type I and the compound twins exhibit the well-defined crystallographic features of those boundaries. Lattice image of the 〈011〉 Type II twin taken from the unique η1 axis suggests that neither ledge nor step structures are present at the irrational boundary..
170. Ryuichi Tomoshige, Akira Chiba, Minoru Nishida, Kihachiro Imamura, Masao Kodama, Toru Matsushita, Microstructures and mechanical properties of shock consolidated TiAl alloy powder compacts, Kayaku Gakkaishi/Journal of the Japan Explosives Society, 55, 4, 166-173, 1994.07, Shock consolidation of TiAl alloy powder produced by plasma rotating electrode process (P-REP) was carried out using underwater-shock consolidation assembly newly developed. Microstructures and mechanical properties were investigated for the obtained compacts. The compacts heat-treated at 973K to 1623K were also observed and tested as well as the as-compacted specimens. As the result, the as-compacted specimens have nearly theoretical density, and attained strong bonding through the thin melting layer generated by friction of the powder particles and adiabatic compression of residual air between the particles. Further, specimen heat-treated at 1623K have microduplex structures with γ+α2 phases. The specimen showed high compressive strength of 1280MPa and high strain of about 32%. From above results, it is concluded that the compacts with excellent mechanical properties were obtained by operating both shock consolidation and heat treatment..
171. Kazuyuki Hokamoto, Akira Chiba, Minoru Nishida, Masahiro Fujita, Experimental conditions for the fabrication of multilayered metal base composite made by single-shot explosive welding technique, QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY, 10.2207/qjjws.12.363, 12, 3, 363-367, 1994.01, Multilayered composites reinforced with steel sheets were tried to be fabricated using single-shot explosive welding technique. The experimental conditions for obtaining moderate bonding at every interface were investigated based on collision velocity (VP) and kinetic energy loss by collision (ΔKE) calculated using finite-difference analysis. In case of aluminum base composite reinforced with stainless steel sheets with the same thickness of multilayered plates, the amount of energy dissipated by collision (ΔKE) should be regulated at a certain range by changing stand-off distances between plates. In case of aluminum and titanium base composite reinforced with maraging steel sheets, moderated welding is unable to be achieved when using the multilayered plates with the same thickness due to a large difference of tensile strength between the components. The use of multilayered plates with the same mass per unit area by regulating the thickness of multilayered plates was useful for obtaining moderate bonding as a means to decrease the difference of ΔKE at each collision of the plates..
172. Yasuhiro Morizono, Minoru Nishida, Akira Chiba, Joining of chromized carbon-steel and Si3N4, Journal of the Ceramic Society of Japan. International ed., 101, 12, 1327-1332, 1993.12, A 0.96 mass%C steel coated with chromium carbides was brazed to Si3N4 by using Ag-Cu/Ti alloy. Chromium carbides were coated on the steel at 1373 K for 2.5 to 36 h in an [Ar+HCl] mixture gas using the Cr powder pack process. The obtained coating layer consisted of M7C3 and M23C6(M = Fe, Cr). The bonding treatment was performed at 1173 K for 1 h in vacuum. The shear strength of the joint increased with increasing coating layer thickness up to 20 μm. The average and maximum shear strengths of the joint with a coating layer of 20 μm in thickness were 209 and 258 MPa, respectively. Those of the joint without the coating layer were 149 and 218 MPa, respectively. The Weibull slopes for the shear strength were 9.4 in the former and 3.8 in the latter. The coating layer was considered to play an important role as an active layer of interfacial reaction and as a relaxation layer of thermal stress in the joint. The difference in interfacial structures between these joints was also discussed on the basis of TEM observation..
173. T. Mashimo, S. Tashiro, T. Toya, Minoru Nishida, H. Yamazaki, S. Yamaya, K. Oh-Ishi, Y. Syono, Synthesis of the B1-type tantalum nitride by shock compression, Journal of Materials Science, 10.1007/BF01159819, 28, 13, 3439-3443, 1993.07, B1-type tantalum nitride (polycrystalline bulk state) was synthesized by shock compression. Shock-compression recovery experiments of the porous sample of tantalum nitride with a hexagonal structure (CoSn-type) were performed in the impact-velocity range up to 1.5kms-1. The instrumental chemical analysis, X-ray and electron diffraction experiments were carried out on the recovered tantalum nitride sample and the combustion-synthesized B1-type sample for comparison. The recovery rate of the B1 -type phase increased with increasing porosity, impact velocity and impactor thickness; among these above all the effect of porosity was most remarkable. Almost 100% recovery rate was achieved for the powder of 70% porosity impacted by a 2 mm thick tungsten plate with velocities above 1.4 kms-1. It was confirmed by chemical analysis that the nitrogen content did not change by shock compression. The chemical formulae of the shock-synthesized and combustioned-synthesized B1-type phases were estimated to be TaN0.96-0.99 and TaN1.13-1.16, 1.27-1.30, respectively. The lattice parameter of the shock-synthesized B1 -type (Fm3m) phase was ao=0.43363- + (1) nm. The results of X-ray and electron diffraction experiments also supported that the shock-synthesized B1-type tantalum nitride has a good stoichiometry compared with the combustion-synthesized ones..
174. Ryuichi Tomoshige, Akira Chiba, Minoru Nishida, Kihachiro Imamura, Shigeru Itoh, Masahiro Fujita, Fabrication and some mechanical properties of SiC whisker-reinforced Si3N4 composites utilizing underwater-shock pressure, Journal of the Ceramic Society of Japan. International ed., 101, 4, 434-440, 1993.04, SiC whisker-reinforced Si3N4-based composites without additives were compacted by underwater-shock wave. The composites contained 10, 20 and 30 vol%SiC whisker as reinforcements. There were no macrocracks in all shock compacted composites. The as-compacted and specimens sintered at various temperatures for 5 h were characterized by the measurements of relative density, micro Vickers hardness and fracture toughness. The relative density of sintered Si3N4-10 vol%SiC whisker composite was higher than that of sintered Si3N4-20 and 30 vol%SiC whisker composites, and reached the theoretical density by sintering at 1973 K. Hardness of each composite increased up to 1823 K in proportion to sintering temperature, and then saturated above 1823 K. The hardness and fracture toughness of the Si3N4-30 vol%SiC whisker composite sintered at 1973 K were about 29 GPa and 5.0 MPa√m, respectively. The fracture toughness was 25% higher than those of monolithic Si3N4 and other obtained composites sintered at the same temperature. SEM observation showed that whisker bridging and deflection were observed in sintered composites and that the matrix of the Si3N4-30 vol%SiC whisker composite consists of plate-like and submicron order fine needle-like β-Si3N4 grains..
175. Minoru Nishida, A. Chiba, K. Imamura, H. Minato, J. Shudo, Microstructural modifications in an explosively welded Ti/Ti clad material
I. Bonding interface, Metallurgical Transactions A, 10.1007/BF02656641, 24, 3, 735-742, 1993.03, Microstructural modifications of the bonding interface in an explosively welded Ti/Ti clad material using the preset angle standoff configuration with various flyer plate speeds have been studied. Explosive welding was completed at flyer plate speed over 420 m/s. The wavelength and amplitude of the wavy interface increased with increasing flyer plate speed up to 1060 m/s. The planar interface was obtained at flyer plate speed of 1150 m/s. The trace of melting was observed at the bonding interface in the present experimental conditions. It is concluded that the melting layer is responsible for the bonding of explosively welded Ti/Ti clad materials. An anomaly hardening zone was formed at the bonding interface in the clad material welded at flyer plate speed of 1150 m/s. The origin of the observed anomalous hardening has also been discussed..
176. Minoru Nishida, A. Chiba, S. Ando, K. Imamura, H. Minato, Microstructural modifications in an explosively welded Ti/Ti clad material
II. Deformation structures around bonding interface, Metallurgical Transactions A, 10.1007/BF02656642, 24, 3, 743-750, 1993.03, The residual deformation structures around the bonding interface in an explosively welded Ti/Ti clad material have been studied by optical microscopy and transmission electron microscopy (TEM). The microstructures around the bonding interface in the clad material welded at flyer plate speed of 420 m/s were consistent with the deformation structures of pure titanium under conventional quasistatic deformation around ambient temperature, except for the development of c + a dislocations just near the bonding interface and the presence of {10-13} twinning. The latter has been newly observed in pure titanium. The deformation modes within 50 μm from the bonding interface in system IV were essentially the same as those in pure titanium under conventional quasistatic deformation at elevated temperatures. The {13-41} twinning has been newly confirmed experimentally and was defined as an active twinning mode under high strain rate and/or at elevated temperatures. The microstructural aspects of adiabatic shear band (ASB) were also described..
177. Ryuichi Tomoshige, Akira Chiba, Minoru Nishida, Kihachiro Imamura, Shigeru Itoh, Masahiro Fujita, Fabrication and some mechanical properties of SiC whisker-reinforced Si3N4 composites utilizing underwater-shock pressure, Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan, 10.2109/jcersj.101.445, 101, 1172, 445-450, 1993.01, SiC whisker-reinforced Si3N4-based composites without additives were compacted by underwater-shock wave. The composites contained 10, 20 and 30 vol% SiC whisker as reinforcements. There were no macrocracks in all shock compacted composites. The as-compacted and specimens sintered at various temperatures for 5h were characterized by the measurements of relative density, micro Vickers hardness and fracture toughness. The relative density of a sintered Si3N4-10 vol% SiC whisker composite was higher than that of sintered Si3N4-20 and 30 vol% SiC whisker composites, and reached the theoretical density by sintering at 1973 K. Hardness of each composite increased up to 1823 K in proportion to sintering temperature, and then saturated above 1823 K. The hardness and fracture toughness of the Si3N4-30 vol% SiC whisker composite sintered at 1973 K were about 29 GPa and 5.0 MPa√m, respectively. The fracture toughness was 25% higher than those of monolithic Si3N4 and other obtained composites sintered at the same temperature. SEM observation showed that whisker bridging and deflection were observed in sintered composites and that the matrix of the Si3N4-30 vol% SiC whisker composite consisted of plate-like and submicron order fine needle-like β-Si3N4 grains..
178. Minoru Nishida, T. Tateyama, R. Tomoshige, K. Morita, A. Chiba, Electron microscopy studies of Ti - 47 at. % Al powder produced by plasma rotating electrode process, Scripta Metallurgica et Materiala, 10.1016/0956-716X(92)90522-G, 27, 3, 335-340, 1992.08.
179. Yasumichi Matsumoto, Jukichi Hombo, Yoshiaki Yamaguchi, Minoru Nishida, Akira Chiba, Origin of the silver doping effects on superconducting oxide ceramics, Applied Physics Letters, 10.1063/1.103218, 56, 16, 1585-1587, 1990.12, The origin of silver doping effects on Y-Ba-Cu-O superconducting ceramics, such as a high-temperature shift of the point at zero resistivity in resistivity measurements and an increase in critical current density, was sought by transmission electron microscopy observations. Sintering was strongly promoted together with suppression of the formation of the liquid phase in the grain boundaries by silver. Consequently, the liquid phase, which is not a superconductor, was not present in almost all the grain boundaries of the silver-doped ceramics, while this phase was present in almost all the grain boundaries in pure ceramics..
180. Yasunari Kaneko, Hiromichi Iwasaki, Yoshitaka Matsumoto, Minoru Nishida, Akihiro Mouri, Akira Chiba, Synthesis and morphological aspects of AlN whiskers from Al powders obtained by spark discharged process, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.39.1347, 39, 445, 1347-1352, 1990.01, Synthesis of AlN whiskers from Al powders obtained by a spark discharged process and their morphology were studied. AlN whiskers were synthesized by nitridation of the compositions in the Al-C system in N2-gas flow at 1450°C for 24 hours. Morphological aspects of the whiskers were observed by a scanning and a transmission electron microscopes. Al powders obtained by the spark discharged process were covered with a thin layer of hydroxide and did not melt nor coalesce up to 1000°C in air. Morphologies of the synthesized whiskers were divided into three types; two single filament types and one bicrystal type. Both of the single filament whiskers had 〈0001〉 growth direction. The growth direction of the latter type deviated about 13 degrees from 〈0001〉 axis. All the whiskers were thin plate-like. The internal defect of whiskers was also described..
181. Akira Chiba, Kazuyuki Hokamoto, Minoru Nishida, Effect of heat treatment on tensile strength of explosively-welded maraging steel/Al and maraging steel/Ti multilayered composites, Nippon Kinzoku Gakkai-si, 53, 12, 1268-1275, 1989.12, Multilayered aluminum and titanium base composite reinforced with 18%Ni maraging steel sheets were fabricated by the single-shot explosive welding technique. Microstructures and tensile strength were examined. The effect of heat treatment on the tensile strength was analyzed based on the rule of mixtures. When the reinforcement exhibits the maximum strength by aging, the ultimate tensile strength of both composites aged after welding is about 1.5 times higher than that of the aged one before welding. The former is slightly higher than that predicted from the rule of mixtures. This increment is attributable to the strengthening by the thin intermetallic compound layer formed by aging. The effect of the thickness of the intermetallic compound layer on the tensile strength of the titanium base composite is also described..
182. Minoru Nishida, A. Chiba, K. Imamura, T. Yamaguchi, H. Minato, Microstructures and mechanical properties of explosively consolidated Ti powder with a pressure medium, Metallurgical Transactions A, 10.1007/BF02670175, 20, 12, 2831-2839, 1989.12, Cylindrical axisymmetric explosive consolidation with a pressure medium has been performed on fine irregular Ti powder. The effects of pressure medium on the consolidation process, micro-structural modifications, and tensile properties of the compacts were investigated. The pressure medium used in the present study was water. An optimum consolidation condition was deter-mined by changing the mass ratio of explosive to the innermost powder container tube plus consolidated powder (E/M ratio). For producing a sound compact, an optimum E/M ratio with-out a pressure medium is about 1.52. This narrow window of optimization is an inherent dis-advantage of the explosive consolidation without a pressure medium. On the contrary, an optimum E/M ratio with a pressure medium is determined to be from 1.80 to 5.14, where neither cracks nor central melt hole are formed in the compact. The presence of the pressure medium is ef-fective in extending the range of the optimum E/M ratio. The relative density (the percentage to the theoretical density) of an as-compacted specimen reaches 95 pct or more under the op-timum condition. Microstructural modifications show that substantial interparticle bonding is achieved by melting the surface of the powder or the powder itself. However, the ultimate tensile strength of an as-compacted specimen is 280 MPa with no ductility. The tensile properties of the compacts can be improved by postsintering treatments. The sintering under the optimum condition (1273 K/2 h) raises the ultimate tensile strength and the elongation to 750 MPa and 14 pct, respectively. The observed effect of postsintering treatment on tensile properties of the compacts can be consistently explained by the modification of microstructure..
183. Akira Chiba, Kazuyuki Hokamoto, Minoru Nishida, Thermal stability and mechanical properties of explosive-welded SUS304 steel wire mesh/Al composite, Nippon Kinzoku Gakkai-si, 52, 8, 826-833, 1988.08, The growth of the reaction layers at the wire-matrix interface in the annealing temperature range from 473 to 873 K and its influence on the strength of the composite using uncoated wire and Ni-coated wire were examined. When using an uncoated wire, the reaction layer was not formed at the wire-matrix interface began to form above 673 K. The reaction layer was composed of FeAl3 and Fe2Al5. When using Ni-coated wire composite, the reaction layer was not formed up to 573 K. At temperatures above 673 K. NiAl3 was formed at the Ni-coated layer, while FeAl3 and Fe2 Al5 were formed at the wire side. The effect of the annealing temperature on the tensile strength of the composite was investigated by annealing at various temperatures for 180 ks. The tensile strength of the uncoated wire composite decreased about 10 MPa compared with the as-welded one and showed a constant value at 473-673 K. Above 773 K, it decreased. In the Ni-coated wire composite, the same tendency was observed and strength showed a maximum value at 673 K. The Ni-coated wire composite was strengthened not only by interdiffusion but also by the formation of intermetallic compounds..
184. Minoru Nishida, C. M. Wayman, A. Chiba, Electron microscopy studies of the martensitic transformation in an aged Ti-51at%Ni shape memory alloy, Metallography, 10.1016/0026-0800(88)90025-0, 21, 3, 275-291, 1988.01, Microstructural aspects of the martensite phase in an aged Ti-51at%Ni alloy containing Ti3Ni4 precipitates have been studied systematically using optical and electron microscopy and electron diffraction. A morphological difference in the martensite phase formed in the solution treated and the aged specimens was confirmed. In the former, a dominance of variants forming a small triangular grouping was observed. Plate-like martensite variants formed along certain preferential directions were found in the latter. (001)M twins were observed as internal defects in the martensite formed in aged specimens. This phenomenon was more notable in specimens including finer precipitates. In these specimens, the internal defects in stress-induced martensite were also (001)M twins. Upon increasing the precipitate size by prolonged aging, the microstructure of the martensite in aged specimens recovers to that observed in solution-treated specimens. The mechanism for the formation of (001)M twins is discussed qualitatively in view of the interaction between the precipitates and the parent phase..
185. Minoru Nishida, C. M. Wayman, Electron microscopy studies of the "Premartensitic" transformations in an aged Ti-51 at%Ni shape memory alloy, Metallography, 10.1016/0026-0800(88)90024-9, 21, 3, 255-273, 1988.01, "Premartensitic" transformations in an aged Ti-51at%Ni shape memory alloy have been studied by means of electrical resistance measurements, and electron diffraction and microscopy. On aging at 500°C or below following solution treatment, premartensitic transitions appear in Ti-51at%Ni. The appearance of the premartensitic transitions is attributable to the formation of Ti3Ni4 precipitates. Crystallographic and morphological aspects of the premartensitic transitions in specimens aged under several conditions are described in detail. The premartensitic behavior of the present aged specimens is essentially the same as that of the ternary TiNiFe [8-10] and TiNiAl alloys [16]..
186. A. Chiba, Minoru Nishida, T. Yamaguchi, J. Tosaka, Explosive consolidation of titanium powder with a pressure medium, Scripta Metallurgica, 10.1016/S0036-9748(88)80336-3, 22, 2, 213-217, 1988.01.
187. Tomio Satoh, Kunio Okimoto, Minoru Nishida, Kihachiro Imamura, Akira Chiba, Improvement of Superplasticity of Zn-22Al Pre-alloy Powder by the Use of Rapid Solidification Technique and Heat-treatment Method, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.35.91, 35, 3, 91-95, 1988.01, Zn-22Al pre-alloy powders were fabricated by air-atomized, argon-atomized and rapidly solidified methods. The rapidly solidified powder was fabricated by centrifugal atomization method. To improve the superplasticity of the air-atomized and argon-atomized powders, a simple heat-treatment of the powders, i.e. rapid cooling after heating at 380°C for half an hour, was attempted. Microstructures of the rapidly solidified and the heat-treated Zn-22Al pre-alloy powders were observed by optical microscope, SEM and TEM. It was found that the microstructures of the heat-treated powders were refined and granulated, and that also the grains became equiaxed in shape. Compactibility of the rapidly solidified powder was inferior to those made from the air-atomized and argon-atomized powders, because the shape of the rapidly solidified powder was nearly spherical. However, the refinement and homogenization of the rapidly solidified powder was almost same to those of the heat-treated powders and elongation of the compact reached about 1000%..
188. Minoru Nishida, C. M. Wayman, Phase transformations in Ti2Ni3 precipitates, Metallurgical transactions. A, Physical metallurgy and materials science, 10.1007/BF02646921, 18, 6, 785-799, 1987.06, The morphology and crystallography of transformation products of Ti2Ni3 in an aged Ti-52.0 at. pct Ni alloy have been studied by means of optical and electron microscopy and electron diffraction. Band-shaped surface relief was observed in optical micrographs at room temperature. Needle and antiphase-like domains were observed in electron micrographs at room temperature. The former correspond to the band-shaped relief seen in optical micrographs. The crystal structure of Ti2Ni3 at room temperature was confirmed to be monoclinic by electron diffraction. The needle-like domains and matrix are twin-related with respect to the {120} plane of the monoclinic structure. Upon heating, first the needle-like domains (low temperature phase) shrank and disappeared at about 50 °C, and then the antiphase-like domains (intermediate phase) disappeared at about 100 °C. Upon subsequent cooling, antiphase-like domains appeared and then needle-like domains appeared. These transformations are reversible upon thermal cycling. The antiphase-like domains in the intermediate phase disappeared with the growth of the needle-like domains and new antiphase-like domains appeared within the needles. The sequence of transformation events in the Ti2Ni3 phase was deduced by electron microscopy and diffraction to be as follows: parent phase (tetragonal) → intermediate phase characterized by antiphase-like domain morphology (orthorhombic) → low temperature phase characterized by needle-like domain morphology (monoclinic). In spite of some differences in crystallographic and morphological changes, the above phenomena are much like the R-phase transition associated with CDW's in TiNiFe alloys..
189. Minoru Nishida, C. M. Wayman, PHASE TRANSFORMATIONS IN Ti//2Ni//3 PRECIPITATES FORMED IN AGED Ti-52 At. Pct Ni., Metallurgical transactions. A, Physical metallurgy and materials science, 18 A, 5, 785-799, 1987.05, The TiNi alloys of near equiatomic composition are one of the most technologically important shape memory alloys. The morphology and crystallography of transformation products of Ti//2Ni//3 in an aged Ti-52. 0 at. pct Ni alloy have been studied by optical and electron microscopy and electron diffraction. The crystal structure at room temperature is confirmed to be monoclinic. The sequence of transformation events was deduced to be as follows: parent phase (tetragonal) yields intermediate phase characterized by antiphase-like domain morphology (orthorhombic) yields low temperature phase characterized by needle-like domain morphology (monoclinic)..
190. Minoru Nishida, C. M. Wayman, Electron microscopy studies of precipitation processes in near-equiatomic TiNi shape memory alloys, Materials Science and Engineering, 10.1016/0025-5416(87)90424-1, 93, C, 191-203, 1987.01, Transmission electron microscopy studies based on pervious data obtained from optical microscopy observations were made of precipitation processes in Ti-50at.%Ni and Ti-52at.%Ni shape memory alloys which had been systematically aged. The precipitation sequence is consistent with previous results obtained using conventional metallographic techniques. Morphological and crystallographic characteristics of the various precipitate phases are described in detail..
191. Minoru Nishida, C. M. Wayman, T. Honma, Precipitation processes in near-equiatomic TiNi shape memory alloys, Metallurgical Transactions A, 10.1007/BF02650086, 17, 9, 1505-1515, 1986.09, Metallographic studies have been made of precipitation processes in Ti-50 pct Ni and Ti-52 pct Ni (at. pct) shape memory alloys. The eutectoid and peritectoid reactions previously reported for near-equiatomic and Ni-rich TiNi alloys were not observed for either composition. In the Ti-52Ni alloy, diffusional transformations take place, similar to those in supersaturated alloys. The precipitation sequence can be written as β
0
→ Ti
11
Ni
14
→ Ti
2
Ni
3
→ TiNi
3
. The solidus line of the TiNi phase in the Ti-52Ni alloy lies at 812 ± 22 °C. Morphological characteristics of the various precipitate phases are described in detail..
192. Minoru Nishida, C. M. Wayman, R. Kainuma, T. Honma, Further electron microscopy studies of the Ti11 Ni14 phase in an aged Ti52at%Ni shape memory alloy, Scripta Metallurgica, 10.1016/0036-9748(86)90463-1, 20, 6, 899-904, 1986.01.
193. Minoru Nishida, C. M. Wayman, T. Honma, Phase transformations in a Ti50Ni47.5Fe2.5 shape memory alloy, Metallography, 10.1016/0026-0800(86)90010-8, 19, 1, 99-113, 1986.01, An optical metallographic study involving surface relief was made of the phase transformations in a Ti50Ni47.5Fe2.5 alloy. The formation and reversion of two different kinds of surface relief associated with R-phase and martensitic transformations were observed upon thermal cycling. The nature of the R-phase transition and its microstructural changes during deformation were also observed; these are described..
194. Minoru Nishida, C. M. Wayman, T. Honma, Electron microscopy studies of the Ti
11
Ni
14
phase in an aged Ti-52.0at%Ni shape memory alloy, Scripta Metallurgica, 10.1016/0036-9748(85)90296-0, 19, 8, 983-987, 1985.01.
195. Minoru Nishida, T. Honma, All-round shape memory effect in Ni-rich TiNi alloys generated by constrained aging, Scripta Metallurgica, 10.1016/0036-9748(84)90125-X, 18, 11, 1293-1298, 1984.01.
196. Minoru Nishida, T. Honma, Effect of heat treatment on the all-round shape memory effect in Ti-5lat%Ni, Scripta Metallurgica, 10.1016/0036-9748(84)90126-1, 18, 11, 1299-1302, 1984.01.
197. Minoru Nishida, C. M. Wayman, T. Honma, Electron microscopy studies of the all-around shape memory effect in a Ti-51.0 at .%Ni alloy, Scripta Metallurgica, 10.1016/0036-9748(84)90371-5, 18, 12, 1389-1394, 1984.01.
198. Minoru Nishida, T. Honma, PHASE TRANSFORMATIONS IN Ti//5//0Ni//5//0//-//xFe//x ALLOYS., Journal de Physique (Paris), Colloque, 43, 1982.12.
199. Toshio Honma, Minoru Matsumoto, Yoshiro Shugo, Minoru Nishida, Isao Yamazaki, EFFECTS OF THERMAL CYCLES AND SUBSTITUTION ELEMENTS ON THE PHASE TRANSFORMATIONS OF TiNi., Unknown Host Publication Title, 1455-1146, 1980.12.