Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Satoshi Hata Last modified date:2018.07.02

Professor / Quantum Physicality Course / Department of Advanced Materials Science and Engineering / Faculty of Engineering Sciences


Papers
1. Kana L. Hasezaki, Hikaru Saito, Takumi Sannomiya, Hiroya Miyazaki, Takashi Gondo, Shinsuke Miyazaki, Satoshi Hata, Three-dimensional visualization of dislocations in a ferromagnetic material by magnetic-field-free electron tomography, Ultramicroscopy, 10.1016/j.ultramic.2017.07.016, 182, 249-257, 2017.11, In conventional transmission electron microscopy, specimens to be observed are placed in between the objective lens pole piece and therefore exposed to a strong magnetic field about 2 T. For a ferromagnetic specimen, magnetization of the specimen causes isotropic and anisotropic defocusing, deflection of the electron beam as well as deformation of the specimen, which all become more severe when the specimen tilted. Therefore electron tomography on a ferromagnetic crystalline specimen is highly challenging because tilt-series data sets must be acquired without changing the excitation condition of a specific diffraction spot. In this study, a scanning transmission electron microscopy (STEM) tomography method without magnetizing a ferromagnetic specimen has been developed for three-dimensional (3D) visualization of dislocations in α-Fe, which is a typical ferromagnetic material. Magnetic-field-free environment down to 0.38 ± 0.07 mT at the specimen position is realized by demagnetizing the objective lens pole piece of a commercial STEM instrument. By using a spherical aberration corrector with the magnetic-field-free environment, an “aberration corrected Low-Mag STEM mode” with no objective lens field reaches a convergence semi angle ∼1 mrad and a spatial resolution ∼5 nm, and shows an adequate performance of imaging dislocations under a two-beam excitation condition for a low-index diffracted beam. The illumination condition for the aberration corrected Low-Mag STEM mode gives no overlap between the direct beam disk (spot) and neighboring diffraction disks. An electron channeling contrast imaging technique, in which an annular detector was located at a doughnut area between the direct beam and the neighboring diffracted beams, was effectively employed with the aberration corrected Low-Mag STEM mode to keep image intensity high enough even at large specimen-tilt angles. The resultant tomographic observation visualized 3D dislocation arrangements and active slip planes in a deformed α-Fe specimen..
2. D. Hirakami, K. Ushioda, T. Manabe, K. Noguchi, K. Takai, Y. Hata, Satoshi Hata, H. Nakashima, Change in the microstructure and mechanical properties of drawn pearlitic steel with low-temperature aging, IOP Conference Series: Materials Science and Engineering, 10.1088/1757-899X/219/1/012026, 219, 1, 2017.08, Hydrogen embrittlement is a serious problem in high-strength steels. Drawn pearlitic steel shows excellent resistance to hydrogen embrittlement despite its high strength, and aging treatment at a low temperature can simultaneously improve its strength and hydrogen-embrittlement resistance. To clarify the mechanism for this we have used thermal desorption analysis (TDA) and the newly developed precession electron diffraction analysis method in the transmission electron microscope. After aging at 100 °C for 10 min, the amount of hydrogen seen amount on the TDA curve reduced at around 100 °C. In contrast, when aging was performed at 300 °C, the hydrogen amount further reduced at around 100 °C and the unevenly deformed lamellar ferrite zone was locally recovered. For the samples that were aged at the low temperature, we confirmed that their yield strength and relaxation stress ratios increased simultaneously with improvement in the hydrogen-embrittlement property. We infer that segregation of carbon or formation of very fine carbide in dislocations during aging is the cause of these behaviors..
3. H. Sosiati, N. Kuwano, Satoshi Hata, Electron Microscopy of the Tin-oxide Nanolayer Formed on the Surface of Sn-Ag-Cu Alloys, IOP Conference Series: Materials Science and Engineering, 10.1088/1757-899X/196/1/012006, 196, 1, 2017.05, Sn-Ag-Cu alloy used in the present study is commercial Sn-3.0Ag-0.5Cu solder ball alloys with a diameter of 400 and 300 μm which were long term atmospheric oxidized for about 6 years (specimen-1) and under high temperature/humidity at 85°C and relative humidity of 85% for 2140 h, respectively. Morphologies and nanostructure of the oxide nanolayers formed on the surface of Sn-Ag-Cu alloys were studied from the interface of the oxide film and the tin substrate by transmission electron microscopy (TEM) to verify the oxidation mechanism. Cross-sectional TEM specimens were prepared using a focused-ion-beam (FIB) micro-sampling technique. Before the FIB fabrication, the specimen surface was coated with carbon (C) and tungsten (W) films. Inhomogeneous thickness of tin-oxide nanolayer formed on specimen-1 and specimen-2 were fluctuated between 20-40 nm and 40-50 nm, respectively. The nanolayer on specimen-1, however, consists of polycrystalline SnO and SnO2, whereas the one on the specimen-2 comprises of polycrystalline SnO2. High resolution (HRTEM) image and fast Fourier transformation (FFT) spectra corresponding to the interface and the substrate areas have confirmed those results. The results verify that at very long atmospheric oxidation Sn was gradually oxidized to be SnO (Sn2+) and then SnO2 (Sn4+), in which SnO is present at the region closed to interface between Sn-substrate and the tin-oxide layer. At high temperature oxidation, however, Sn was completely oxidized to be SnO2..
4. Satoshi Hata, S. Miyazaki, T. Gondo, K. Kawamoto, N. Horii, K. Sato, H. Furukawa, H. Kudo, H. Miyazaki, M. Murayama, In-situ straining and time-resolved electron tomography data acquisition in a transmission electron microscope, Microscopy (Oxford, England), 10.1093/jmicro/dfw109, 66, 2, 143-153, 2017.04, This paper reports the preliminary results of a new in-situ three-dimensional (3D) imaging system for observing plastic deformation behavior in a transmission electron microscope (TEM) as a directly relevant development of the recently reported straining-and-tomography holder [Sato K et al. (2015) Development of a novel straining holder for transmission electron microscopy compatible with single tilt-axis electron tomography. Microsc. 64: 369-375]. We designed an integrated system using the holder and newly developed straining and image-acquisition software and then developed an experimental procedure for in-situ straining and time-resolved electron tomography (ET) data acquisition. The software for image acquisition and 3D visualization was developed based on the commercially available ET software TEMographyTM. We achieved time-resolved 3D visualization of nanometer-scale plastic deformation behavior in a Pb-Sn alloy sample, thus demonstrating the capability of this system for potential applications in materials science..
5. Wan song Li, Hong ye Gao, Hideharu Nakashima, Satoshi Hata, Wen huai Tian, In-situ EBSD study of deformation behavior of retained austenite in a low-carbon quenching and partitioning steel via uniaxial tensile tests, Materials Characterization, 10.1016/j.matchar.2016.06.020, 118, 431-437, 2016.08, Through using in-situ electron back-scattered diffraction and uniaxial tensile tests, this work mainly focuses on the deformation behavior of retained austenite (RA) in a low-carbon quenching and partitioning (Q&P) steel. In this paper, three different types of RA can be distinguished from different locations, respectively, RA grains at the triple edges, twinned austenite and RA grains positioned between martensite. The results have shown that grains at the triple edges and twinned austenite could transform easily with increasing strain, i.e. are less stable when compared with RA grains distributed between martensite that could resist a larger plastic deformation. Meanwhile, the strain leads to rotations of RA grains distributed at the triple edges and between martensite. Moreover, RA grains with a similar orientation undergone similar rotations with the same true strain. These RA grains rotated along a specific slip plane and slip direction and the grain rotation is taken as a significant factor to improve the ductility of steel. In addition, grain sizes of RA decreased gradually with an increase of true strain and smaller (0–0.2 μm) grains were more capable of resisting the deformation. According to kernel average misorientation (KAM) analysis, it can be found that strain distribution is preferentially localized near martensite–austenite phase boundaries and in the interior of martensite. The average KAM values increased continuously with increasing true strain..
6. Wan song Li, Hong ye Gao, Hideharu Nakashima, Satoshi Hata, Wen huai Tian, Microstructural evolution and mechanical properties of a low-carbon quenching and partitioning steel after partial and full austenitization, International Journal of Minerals, Metallurgy and Materials, 10.1007/s12613-016-1306-0, 23, 8, 906-919, 2016.08, In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected..
7. Chanmin Lee, Yukwon Jeon, Satoshi Hata, Joo Il Park, Ryutaro Akiyoshi, Hikaru Saito, Yasutake Teraoka, Yong Gun Shul, Hisahiro Einaga, Three-dimensional arrangements of perovskite-type oxide nano-fiber webs for effective soot oxidation, Applied Catalysis B: Environmental, 10.1016/j.apcatb.2016.03.001, 191, 157-164, 2016.08, Perovskite-type oxides have been widely applied in heterogeneous catalytic reactions, such as soot oxidation. However, a poor contact point between the catalyst and solid reactant (soot) often limits the catalytic performance. Here, we report La1 - xSrxCo0.2Fe0.8O3 - δ perovskite oxide catalysts with a unique three-dimensional (3D) fiber web structure that increases the high-contact area by trapping soot in the unique pore structure for effective catalytic activity. This feature was carefully analyzed using scanning transmission electron microscopy (STEM) tomography to investigate the location of the soot on the web. The structure of the web, with a thickness of approximately 55 μm, indicated that the soot particles were caught by the 3D pores between the fibers. The relationship between the Sr amount and activate oxygen was also characterized by means of XPS. The results show that the Sr amount of 0.4 produced the highest amount of active oxygen species (O-) that are essential for soot oxidation reaction. The developed catalyst exhibited a good catalytic performance due to the optimized perovskite chemical structure and the greatly increased number of the contact points owing to the 3D inter-fiber spaces. Hence, our proposed approach is reasonable for application to real soot combustion processes and can also be easily extended to numerous other catalytic processes to enhance the catalytic activity..
8. Toshihiro Tsuchiyma, Shinji Yamamoto, Satoshi Hata, Mitsuhiro Murayama, Satoshi Morooka, Daichi Akama, Setsuo Takaki, Plastic deformation and dissolution of ϵ-Cu particles by cold rolling in an over-aged particle dispersion strengthening Fe-2mass%Cu alloy, Acta Materialia, 10.1016/j.actamat.2016.03.018, 113, 48-55, 2016.07, Deformation and dissolution behaviors are important characteristics of soft dispersion particles in steel to improve the deformability of high strength steel sheets by controlling the work hardening/softening and fracture processes associated with particle dispersion strengthening. In this study, the deformation and dissolution behaviors of ϵ-Cu precipitate particles in a ferrite matrix were investigated to understand how relatively soft dispersion particles influence mechanical responses of the steel compared to hard dispersion particles such as alloy carbides. 35 nm diameter nearly spherical ϵ-Cu particles were initially elongated along the rolling direction by cold rolling, and then these were partly dissolved into the ferrite matrix as the equivalent strain increased. The dissolution of the Cu particles was suggested to be caused by a dynamic partitioning of Cu atoms from the precipitates into the matrix by dislocation shearing at the particle tip sharpened by severe cold working. Simultaneously, the contribution of the ϵ-Cu particles to the dispersion strengthening appeared to be decreased with increasing dislocation density in the matrix during cold rolling. The dislocation density and other defects in the ϵ-Cu particles also increased and the particle/matrix interfaces were serrated or became indistinct as deformation progressed. The morphology, internal defects, and interface structure changes of fine dispersion particles and their correlation with mechanical responses of the alloy are discussed in reference to an identically processed, hard particles dispersed Fe-V binary alloy..
9. Jun jie SHEN, Ken ichi IKEDA, Satoshi Hata, Hideharu Nakashima, Primary-transient creep and anelastic backflow of pure copper deformed at low temperatures and ultra-low strain rates, Transactions of Nonferrous Metals Society of China, 10.1016/S1003-6326(16)64285-1, 26, 7, 1729-1735, 2016.07, Creep and anelastic backflow behaviors of pure copper (4N Cu) with grain size dg=40 μm were investigated at low temperatures of T<0.3Tm (Tm is melting point) and ultra-low creep rates of ɛ˙=1×10−10s−1 by a high strain-resolution measurement (the helicoid spring specimen technique). Analysis of creep data was based on the scaling factors of creep curves instead of the conventional extrapolated steady-state creep rate. Power-law creep equation is suggested to be the best for describing the primary transient creep behavior, because the pre-parameter does not apparently change with elapsed time. The observed anelastic strains are 1/6 of the calculated elastic strains, and linear viscous behavior was identified from the logarithm plot of the anelastic strain rate versus anelastic strain (slope equals 1). Therefore, the creep anelasticity is suggested to be due to the unbowing of there-dimensional network of dislocations..
10. Jesbains Kaur, Noriyuki Kuwano, Khairur Rijal Jamaludin, Masatoshi Mitsuhara, Hikaru Saito, Satoshi Hata, Shuhei Suzuki, Hideto Miyake, Kazumasa Hiramatsu, Hiroyuki Fukuyama, Electron microscopy analysis of microstructure of postannealed aluminum nitride template, Applied Physics Express, 10.7567/APEX.9.065502, 9, 6, 2016.06, The microstructure of an AlN template after high-temperature annealing was investigated by transmission electron microscopy (TEM). The AlN template was prepared by depositing an AlN layer of about 200nm thickness on a sapphire (0001) substrate by metal-organic vapor phase epitaxy. The AlN template was annealed under (N2 + CO) atmosphere at 1500-1650 °C. TEM characterization was conducted to investigate the microstructural evolution, revealing that the postannealed AlN has a two-layer structure, the upper and lower layers of which exhibit Al and N polarities, respectively. It has been confirmed that postannealing is an effective treatment for controlling the microstructure..
11. K. Jesbains, N. Kuwano, K. R. Jamaludin, H. Miyake, K. Hiramatsu, S. Suzuki, Masatoshi Mitsuhara, Satoshi Hata, Y. Soejima, Reduction of dislocation density of aluminium nitride buffer layer grown on sapphire substrate, Journal of Mechanical Engineering and Sciences, 10.15282/jmes.10.1.2016.14.0182, 10, 1, 1908-1916, 2016.06, An aluminium nitride (AlN) buffer layer with 200 nm thickness was grown on (0001) sapphire substrate using the metal-organic vapour phase epitaxy (MOVPE) method in a low-pressure furnace, followed by a clean-up treatment of sapphire substrate at 1100°C. Thereafter, the AlN buffer layer was annealed at a high temperature in the range of 1500°C to 1700°C for 2 hours under the atmosphere of N2+CO. The objective of this research is to determine the microstructure changes with different annealing temperatures. Cross-sectional TEM has revealed that, after annealing at 1500°C, two types of defects remained in the AlN buffer layer: inverted cone shape domains and threading dislocations. The former domains were observed in an image taken with diffraction of g=0002, but not in an image with g=1010. The morphology and the diffraction condition for the image contrast strongly, suggesting that the domains are inversion domains. The threading dislocations were invisible in the image taken with the diffraction of g=0002, revealing that they were a-Type dislocations. However, after annealing at 1600oC, the inversion domains coalesced with each other to give a two-layer structure divided by a single inversion domain boundary at the centre of the AlN buffer layer. The density of threading dislocation was roughly estimated to be 5×109 cm-2 after annealing at 1500°C, and to be reduced to 5×108 cm-2 after annealing at 1600°C. These experimental results validate the fact that the annealing temperature around 1600°C is high enough to remove the defects by the diffusion process. Therefore, it was discovered that high temperature annealing is an effective treatment to alter the microstructure of AlN thin films and remove defects by the diffusion process. Annealing at high temperature is recommended to increase the emission efficiency for fabrication of optoelectronic devices..
12. Wan song Li, Hong ye Gao, Zhong yi Li, Hideharu Nakashima, Satoshi Hata, Wen huai Tian, Effect of lower bainite/martensite/retained austenite triplex microstructure on the mechanical properties of a low-carbon steel with quenching and partitioning process, International Journal of Minerals, Metallurgy and Materials, 10.1007/s12613-016-1239-7, 23, 3, 303-313, 2016.03, We present a study concerning Fe–0.176C–1.31Si–1.58Mn–0.26Al–0.3Cr (wt%) steel subjected to a quenching and partitioning (Q&P) process. The results of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests demonstrate that the microstructures primarily consist of lath martensite, retained austenite, lower bainite (LB), and a small amount of tempered martensite; moreover, few twin austenite grains were observed. In the microstructure, three types of retained austenite with different sizes and morphologies were observed: blocky retained austenite (~300 nm in width), film-like retained austenite (80–120 nm in width), and ultra- fine film-like retained austenite (30–40 nm in width). Because of the effect of the retained austenite/martensite/LB triplex microstructure, the specimens prepared using different quenching temperatures exhibit high ultimate tensile strength and yield strength. Furthermore, the strength effect of LB can partially counteract the decreasing strength effect of martensite. The formation of LB substantially reduces the amount of retained austenite. Analyses of the retained austenite and the amount of blocky retained austenite indicated that the carbon content is critical to the total elongation of Q&P steel..
13. Sumiha Ikeshita, Ansis Strodahs, Zineb Saghi, Kazuhiro Yamada, Pierre Burdet, Satoshi Hata, Ken ichi Ikeda, Paul A. Midgley, Kenji Kaneko, Hardness and microstructural variation of Al-Mg-Mn-Sc-Zr alloy, Micron, 10.1016/j.micron.2015.12.002, 82, 1-8, 2016.03, Variations of Vickers hardness were observed in Al-Mg-Mn alloy and Al-Mg-Mn-Sc-Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54ks down to 67.4 HV at 360ks, below the initial hardness value, 71.8 HV at 0ks for the case of Al-Mg-Mn-Sc-Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al3Sc1-xZrx and also block-shaped Al3Sc precipitates growing along <100>Al with facets {100} and {110} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al3Sc..
14. W. S. Li, H. Y. Gao, Hideharu Nakashima, Satoshi Hata, W. H. Tian, In-situ study of the deformation-induced rotation and transformation of retained austenite in a low-carbon steel treated by the quenching and partitioning process, Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 10.1016/j.msea.2015.09.076, 649, 417-425, 2016.01, We report an in-situ study of the deformation-induced rotation and transformation of austenite grains in a low-carbon steel treated by the quenching and partitioning process using electron back-scattered diffraction and uniaxial tension experiments. It was found that retained austenite could be classified into four types according to different locations in the microstructure: retained austenite at triple edges, twinned austenite, retained austenite distributed between martensite and retained austenite embedded completely in a single ferrite. The results showed that at the early stage of deformation, the retained austenite at the triple edges and twinned austenite transformed easily, while the retained austenite at the boundaries between martensite and that embedded completely in a single ferrite rotated with no transformation; and did not transform until a large deformation was provided. This phenomenon implies that the retained austenite at the boundaries between martensite and that embedded completely in a single ferrite are more capable of resisting deformation. From the observations of Schmid factor maps and the texture of retained austenite, it can be concluded that the rotation of retained austenite followed a particular slip plane and slip direction. Moreover, the rotation of retained austenite could improve the ductility of the material. In comparison with the film-like retained austenite distributed between martensite, the retained austenite embedded completely in a single ferrite could resist a larger rotation angle, i.e. the latter could contribute more to the ductility of the steel. In addition, from the analysis of kernel average misorientation that the strain distribution mainly concentrated near the α - γ phase boundaries and in the interior of martensite, and the rotation angles and dislocation density of austenite increase with increasing strain..
15. Yusuke Shimada, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Syo Matsumura, Hiroya Tanaka, Akiyasu Yamamoto, Jun Ichi Shimoyama, Kohji Kishio, Microstructural connectivity in sintered ex-situ MgB2 bulk superconductors, Journal of Alloys and Compounds, 10.1016/j.jallcom.2015.09.253, 656, 172-180, 2016.01, We have performed combined high-resolution microstructural and grain orientation analyses to understand the key microstructural factors associated with high intergranular transport current in polycrystalline bulk forms of MgB2. The ex-situ method can produce MgB2 with relatively high packing factors; nevertheless, the connectivity of MgB2 fabricated by the ex-situ method (ex-situ MgB2) was less than that of in-situ MgB2. The poor connections between MgB2 grain aggregates cause the low connectivity of ex-situ MgB2. Plate-like pores are present between the aggregates of MgB2 grains in ex-situ MgB2; these pores remain even after prolonged self-sintering at high temperatures. In addition, MgB2 crystals decompose to MgB4 in sintering for a long period. Moreover, MgO particles are formed between MgB2 grain aggregates and inhibit interaggregate connections. In contrast, in-situ MgB2 fabricated at the same sintering conditions exhibits spherical pores between MgB2 grains, resulting in a uniform pore distribution and intergranular connection. These problems must be addressed to further enhance the connectivity in ex-situ MgB2..
16. Daisuke Hirakami, Toshiyuki Manabe, Kohsaku Ushioda, Kei Noguchi, Kenichi Takai, Yoshinori Hata, Satoshi Hata, Hideharu Nakashima, Effect of aging treatment on hydrogen embrittlement of drawn pearlitic steel wire, ISIJ International, 10.2355/isijinternational.ISIJINT-2015-735, 56, 5, 893-898, 2016, Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. As-drawn pearlitic steel wire is well known to have superior resistance to hydrogen embrittlement. The resistance to hydrogen embrittlement is clarified as being further improved by aging treatment at 100-°C and 300-°C for 10-min. of as-drawn 0.8 mass% C pearlitic steel wire with-5.0 mm (=1.9). The higher the aging temperature is, the better the resistance to hydrogen embrittlement becomes. Simultaneously, the strength even increased slightly by aging treatment. The mechanism is investigated by exploiting thermal desorption analysis (TDA) and the newly developed TEM precession analysis. Aging at 100-°C led to a decrease in the hydrogen content at peak I around 100-°C in the TDA curve, which is inferred to be caused by C segregation to dislocations resulting in improvement of hydrogen embrittlement. Aging at 300-°C further improved the resistance to hydrogen embrittlement, which is presumably brought about by the local recovery of the heterogeneously deformed lamellar ferrite area together with the C segregation to dislocations. Here, the strength increased slightly by aging due to the softening factor of recovery and the hardening factor of strain aging..
17. Ken Ichi Ikeda, Takuya Takashita, Ryutaro Akiyoshi, Satoshi Hata, Hideharu Nakashima, Kazuhiro Yamada, Kenji Kaneko, Effects of scandium and zirconium addition on recrystallization behavior of Al-Mg-Si alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 66, 11, 609-616, 2016, The effects of thermally stabilized particles in Al-Mg-Si alloy on recrystallization behavior were investigated to obtain fundamental knowledge to control microstructure, texture and mechanical properties of this alloy. In this study, the Al-Mg-Si-Sc-Zr alloy was cast, homogenized and hot rolled. Three types of spherical Al3(Sc, Zr) particles with L12 structure: Rod-like incoherent, spherical semi-coherent and spherical incoherent particles were observed in the hot-rolled sample in the Al-Mg-Si-Sc-Zr alloy by using TEM, STEM and EDS. In addition, it was found that all particles have the core-shell structure with the core enriched with Sc and the shell enriched with Zr atoms by 3D-ET and STEM-EDS. It is considered that these particles are formed during casting, homogenized treatment and hot rolling. The results of crystal orientation distribution of annealed sample after cold rolling indicated that the presence of Al3(Sc, Zr) particles may interfere with the recrystallization (the grain growth) until 600°C. From the comparison with the driving force of primary recrystallization and grain growth, and the pinning force of Al3(Sc, Zr) particles, it was suggested that these particles mainly contribute to the suppression of grain growth. The results of in-situ heating SEM/EBSD analysis of cold rolled Al-Mg-Si-Sc-Zr alloy supported the suggestion..
18. Satoshi Hata, Issues of experimental apparatuses for electron tomography observation in crystalline materials, Microscopy (Oxford, England), 10.1093/jmicro/dfw083, 65, i16, 2016, The author has contributed to developing sample holders for electron tomography (ET) [1, 2]. Based on the author’s experience of the holder development, there are distinctive issues of designing ET holders. Because ET usually needs high-angle sample tilt over 60 degrees, the information of a pole piece gap in a transmission electron microscope (TEM) is necessary and also unsatisfactory for designing sample holders capable of ET observation. Firstly, the eucentric height of a sample holder may not locate at the center of the pole piece gap. Secondly, there may not be an enough space (vertical and horizontal widths) outside the pole piece gap. These issues in the TEM sample chamber make the compatibility of high-angle tilt and desirable functions in an ET sample holder difficult. It is also an issue for ET that insertion of an objective aperture limits the maximal sample-tilt angle in modern TEMs of which the objective lens systems are optimized for high-resolution scanning transmission electron microscopy (STEM) as well as transmission electron microscopy (TEM). Therefore, using an objective aperture for diffraction contrast ET observation [3, 4] is not available in these modern TEMs. Alternative diffraction contrast ET observation methods without using an objective aperture have been reported [5, 6]. Fast tilt-series datasets acquisition for time-resolved ET [7] needs superior performances of a TEM goniometer system as well as an image acquisition system. Based on the author‘s experience of fast tilt-series datasets acquisition [8], the followings are issues of the goniometer system for high-resolution time-resolved ET imaging: controllable sample tilt speed at a user level; accurate readout of sample tilt angles synchronizing with image acquisition; (iii) a stable eucentric position of a field of view during sample tilt..
19. R. G Abhilash Kumar, Satoshi Hata, Ken Ichi Ikeda, K. G. Gopchandran, Organic mediated synthesis of highly luminescent Li+ ion compensated Gd2O3
Eu3+ nanophosphors and their Judd-Ofelt analysis, RSC Advances, 10.1039/c5ra26095g, 6, 71, 67295-67307, 2016, Highly luminescent red emitting Gd2O3:Eu3+, Li+ nanophosphor has been synthesized by the solvothermal combustion of the metal-citrate complex in diethylene glycol medium. The morphology and luminescence properties of these nanophosphors are found to be highly sensitive to the extent of lithium ion compensation. It is found that lithium ions promote grain growth and alter the morphology of the Gd2O3:Eu3+ nanophosphor from nearly spherical to cobblestone like. A significant enhancement in intensity of luminescence and quantum efficiency is observed in lithium compensated nanophosphors. The highest emission intensity is observed for the Gd1.75Eu0.1Li0.15O3 nanophosphor, about 1.83 times that of Gd1.9Eu0.1O3 and is attributed to the enhanced intra 4f-4f emission transitions arising from the modifications of the crystal field and distortion of the local symmetry around the europium ions. The luminescence decay profiles are found to be single exponential in nature and the lifetime measured was 1.36 ms for the Gd1.75Eu0.1Li0.15O3 nanophosphor. The chromaticity coordinates of these nanophosphors indicated high colour purity. Judd-Ofelt intensity parameters indicated that lithium compensation increases the polarization of the local environment and an increase of covalency and asymmetry around the europium ions..
20. Nobuo Nakada, Ken Ichi Ikeda, Hiroshi Shuto, Tatsuo Yokoi, Toshihiro Tsuchiyma, Satoshi Hata, Hideharu Nakashima, Setsuo Takaki, Quantification of large deformation with punching in dual phase steel and change of its' microstructure - Part II
Local strain mapping of dual phase steel by a combination technique of electron backscatter diffraction and digital image correlation methods, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.TETSU-2015-086, 102, 5, 253-259, 2016, To evaluate heterogeneous strain distribution developed by pre-deformations in dual phase (DP) steel accurately, a combinational technique of Electron Backscatter Diffraction (EBSD) and Digital Image Correlation (DIC) methods was newly introduced in this study. A good correlation is established between kernel average misorientation calculated by EBSD and local equivalent strain measured by DIC in ferrite matrix of DP steels regardless of the difference in deformation process, which means that an EBSD orientation map can be easily converted into an applicative strain map by employing the individual correlation formula. This new technique reveals that very high strain region is locally formed within dozens of micrometer from the punched edge in a punched DP steel. On the other hand, hard martensite grains dispersed in DP steel remarkably promote the heterogeneity of strain distribution in ferrite matrix. As a result, the high strain region is also developed in the form of bands in a cold-rolled DP steel by only 60% thickness reduction at least, as if it is affected by the distribution and morphology of martensite grains. In addition, the local strain mapping demonstrates that the equivalent strain of the high strain band in cold-rolled material is comparable to that of the heavily deformed edge in punched one. The very high strain band in ferrite matrix is characterized by ultrafine grained structure, which leads to the possibility for the losing ductility in ferrite matrix and the martensite cracking..
21. Nobuo Nakada, Ken Ichi Ikeda, Hiroshi Shuto, Tatsuo Yokoi, Toshihiro Tsuchiyma, Satoshi Hata, Hideharu Nakashima, Setsuo Takaki, Quantification of large deformation with punching in dual phase steel and change of its microstructure - Part II
Local strain mapping of dual phase steel by a combination technique of electron backscatter diffraction and digital image correlation methods, ISIJ International, 10.2355/isijinternational.ISIJINT-2016-310, 56, 11, 2077-2083, 2016, To evaluate heterogeneous strain distribution developed by pre-deformations in dual phase (DP) steel accurately, a combinational technique of Electron Backscatter Diffraction (EBSD) and Digital Image Correlation (DIC) methods was newly introduced in this study. A good correlation is established between kernel average misorientation calculated by EBSD and local equivalent strain measured by DIC in ferrite matrix of DP steels regardless of the difference in deformation process, which means that an EBSD orientation map can be easily converted into an applicative strain map by employing the individual correlation formula. This new technique reveals that very large strain region is locally formed within dozens of micrometer from the punched edge in a punched DP steel. On the other hand, hard martensite grains dispersed in DP steel remarkably promote the heterogeneity of strain distribution in ferrite matrix. As a result, the large strain region is also developed in the form of bands in a cold-rolled DP steel by only 60% thickness reduction at least, as if it is affected by the distribution and morphology of martensite grains. In addition, the local strain mapping demonstrates that the equivalent strain of the large strain band in cold-rolled material is comparable to that of the heavily deformed edge in punched one. The very large strain band in ferrite matrix is characterized by ultrafine grained structure, which leads to the possibility for the losing ductility in ferrite matrix and the martensite cracking..
22. Yoshimitsu Hishinuma, Akihiro Kikuchi, Yusuke Shimada, Taro Kashiwai, Satoshi Hata, Shuichi Yamada, Takeo Muroga, Akio Sagara, Development of MgB2 superconducting wire for the low activation superconducting magnet system operated around core D-T plasma, Fusion Engineering and Design, 10.1016/j.fusengdes.2015.05.005, 98-99, 1076-1080, 2015.10, MgB2 is one of the "low activation superconductors", because the half-life of the induced radio-activity on the MgB2 is much shorter than that of Nb-based superconductors such as NbTi, Nb3Sn and Nb3Al. MgB2 wire would become an alternative material for Nb-Ti wire for the Poloidal Field and correction feedback coils, if the critical current density (Jc) around the magnetic field of 4 T could be improved. We found that addition of Cu using the compound Mg2Cu was an effective method to enhance Jc and succeed to fabricate 100 m length of MgB2 wire with Cu addition. Jc of the 100 m long MgB2 with Cu addition was comparable to that of a NbTi wire, and the small solenoid coil using Cu added MgB2 wire reached a central magnetic field of 2.62 T. We found that MgB2 wire is an alternative material to commercial NbTi wires under the hard neutron irradiation in a fusion reactor. Furthermore, we also fabricated a Cu added MgB2 wire using isotope pure boron-11 (11B) powder as the boron source to reduce the radioactivity. The critical temperature (Tc) of the MgB2 wire using 11B powder was found to be 37 K, and Tc was found to be changed by different boron materials..
23. J. Wang, Satoshi Hata, Y. K. Takahashi, H. Sepehri-Amin, B. S.D.Ch S. Varaprasad, T. Shiroyama, T. Schrefl, K. Hono, Effect of MgO underlayer misorientation on the texture and magnetic property of FePt-C granular film, Acta Materialia, 10.1016/j.actamat.2015.03.007, 91, 41-49, 2015.06, A transmission electron microscope (TEM) based orientation mapping technique and micromagnetic simulations were applied to study the influence of easy axis distribution (EAD) on magnetic properties of FePt-C granular films which were deposited on a single crystalline MgO (0 0 1) substrate and a (0 0 1)-textured poly-crystalline MgO underlayer. The FePt-C film on the polycrystalline MgO underlayer shows smaller perpendicular coercivity, broader switching field distribution and visible in-plane minor loop compared with that deposited on the single crystalline MgO (0 0 1) substrate. Although the grain sizes and their distributions in both films look similar in TEM, orientation mapping and texture analysis revealed that the polycrystalline MgO underlayer introduces significant misorientation in the (0 0 1)-textured FePt grains. Micromagnetic simulations successfully reproduced the large hysteresis in the in-plane magnetization by introducing the specific misorientation distribution of the FePt grains obtained from the texture analysis. The misoriented FePt grains were found to be grown from misoriented MgO grains, indicating that the improvement of the (0 0 1) texture of the MgO underlayer is essential to reduce the in-plane component of FePt based recording media..
24. A. Matsumoto, H. Kitaguchi, T. Doi, T. Izumi, Y. Hakuraku, Y. Shimada, Satoshi Hata, Effect of annealing DC-sputtered Bi,Pb-2223 thin films, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2014.2376193, 25, 3, 2015.06, Thin films of Bi-2223 fabricated on SrTiO3(100) substrates by dc sputtering were found to have a transition temperature (Tc) as low as that of bulk-phase Bi-2223. Subsequent annealing of these precursor films in the presence of Bi,Pb-2223 pellets increased this Tc value from 72 to 105 K, making it comparable to bulk-phase Bi,Pb-2223. Strong (00l) peaks and a sharp quadrupole were observed in this annealed film, indicating a main phase of Bi,Pb-2223 with a c-axis orientation by the X-ray diffractometry (XRD) measurements. A maximum critical current density (Jc) of 3.3 × 105 A/cm2 at 77 K was also obtained with the Bi,Pb-2223 thin film, which is a value that is much higher than that of commercial Bi,Pb-2223 tapes. Jc values of thin films were strongly dependent on the annealing temperatures between 854 °C and 866 °C. In this temperature range, XRD data show that the thin films were not a single phase of Bi,Pb-2223, suggesting only a slight interruption of the supercurrent. Although, the films have a good c-axis and ab-axis alignments. Thus, although the films were not perfect, the improvement in microstructure allows for a much higher Jc value..
25. Yusuke Shimada, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Syo Matsumura, Hiroya Tanaka, Akiyasu Yamamoto, Jun Ichi Shimoyama, Kohji Kishio, Microstructural characteristics of ball-milled self-sintered ex situ MgB2 bulks, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2014.2379928, 25, 3, 2015.06, The ex situ method yields MgB2 samples with high packing factor. However, the critical current density of MgB2 bulks and wires fabricated using the ex situ method (ex situ MgB2) requires improvement for practical use because of insufficient connectivity. In this study, we evaluated the microstructure of self-sintered ex situ MgB2 bulks fabricated from laboratory-made ball-milled powder. We observed that green compacts of the ball-milled bulks contain fine MgB2 grain aggregates and a decreased gap length between MgB2 grain aggregates compared with those prepared without ball-milling. Therefore, the number of connections between the MgB2 grain aggregates and current path increased. However, the width of the connections between MgB2 grain aggregates remained narrow, suggesting the importance of controlling the initial microstructure of green compacts, such as the size of MgB2 grain aggregates and packing factor, by optimizing milling and pressing conditions..
26. Yusuke Shimada, Takato Kajihara, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Akiyoshi Matsumoto, Hitoshi Kitaguchi, Toshiya Doi, Microstructural studies of the effect of heat-treatment on Bi,Pb-2223 films prepared by RF sputtering, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2014.2382874, 25, 3, 2015.06, The uniform single phase Bi,Pb-2223 films are needed in order to acquire fundamental superconductivity data for the development of Bi,Pb-2223 wires. However, Bi,Pb-2223 films that we previously reported had the non-uniform microstructure containing several other phases. In this study we investigated the microstructural evolution during the heat treatment and processing route to fabricate uniform Bi,Pb-2223 films elucidated. An as-grown film had a small amount of Bi-2223 phase and a large amount of Ca-Sr-Cu-O phase. C-axes of some Bi-2223 crystals are not aligned along the normal direction of the STO substrate. In the primary stage of heat treatment, the formation of Bi,Pb-2223 phase proceeds. In the second stage of heat treatment, although the flat Cu-O layers in the Bi,Pb-2223 phase are formed by liquid-phase reactions, the grain coarsening of Ca-Sr-Cu-O phase also occurs. From the observation results, the fabrication process should be optimized based on the following points: uniform dispersion of penetration (diffusion) paths of Pb atoms into the film; short duration of heat treatment to avoid phase separation of Bi,Pb-2223 and coarsening of Ca-Sr-Cu-O phase..
27. Shigeto Yamasaki, Masatoshi Mitsuhara, K. Ikeda, Satoshi Hata, Hideharu Nakashima, 3D visualization of dislocation arrangement using scanning electron microscope serial sectioning method, Scripta Materialia, 10.1016/j.scriptamat.2015.02.001, 101, 80-83, 2015.05, We performed the three-dimensional visualization of dislocations through serial sectioning and use of SEM electron channeling contrast (ECC) images for a crept nickel-based alloy. We successfully reconstructed a volume of approximately 7.5 μm3, including dislocation arrangements, by performing calculations based on the continuous tomograms of ECC images. By incorporating the information on crystal orientation obtained by the electron back-scattered diffraction, we verified that the three-dimensional arrangement of dislocations, such as slip plane, was accurately reflected in the three-dimensional volume..
28. Masaharu Tsuji, Koichi Takemura, Chihiro Shiraishi, Koji Ikedo, Keiko Uto, Atsuhiko Yajima, Masashi Hattori, Yukinori Nakashima, Kento Fukutomi, Kunihiko Tsuruda, Takeshi Daio, Takeshi Tsuji, Satoshi Hata, Syntheses of Au@PdAg and Au@PdAg@Ag core-shell nanorods through distortion-induced alloying between Pd shells and Ag atoms over Au nanorods, Journal of Physical Chemistry C, 10.1021/jp509340s, 119, 20, 10811-10823, 2015.05, Noble Au@PdAg and Au@PdAg@Ag core-shell nanorods (NRs) having PdAg alloy shells were synthesized using Au@Pd NRs as seeds. Their crystal structures and growth mechanisms were examined using data from TEM, TEM-EDS, XRD, and UV-Vis-NIR extinction spectroscopy. First, cuboid or dumbbell-type Au@Pd NR seeds were prepared using Au NRs as seeds. In the second step, when Ag+ ions were reduced over these seeds, cuboid and dumbbell-type Au core PdAg alloy shell NRs were formed with maximum Ag content of about 16% and 24%, respectively, after heating at 60 °C. The driving force of alloying between Pd shells and Ag atoms was attributed to the distortion of Pd layers over Au NRs based on peak shifts and broadening of XRD data. The higher Ag content in dumbbell-type Au@PdAg NRs was explained by the greater distortion of Pd shells over Au NRs. When the Ag content exceeds its maximum solubility in Pd shells, the third Ag shells were grown over Au@PdAg NRs. For cuboid Au@PdAg NRs, the crystal growth of Ag shells over cuboid Au@PdAg cores begins with the formation of single nuclei on a wide side PdAg alloy facet, followed by growth to one cuboid rod shell and further growth of one or two neighboring cuboid rod shells having {100} facets. On the other hand, for dumbbell-type Au@Pd NRs, Ag shells were deposited over concave curvature of the side facets of Au@PdAg and cuboid Au@PdAg@Ag NRs having one large cuboid Ag block was finally formed in each particle. Our study provides a new simple technique for the epitaxial growth of uniform PdAg alloy layers using spontaneous alloying between Pd shells and Ag atoms over Au NRs..
29. Yoji Miyajima, Shin Ya Komatsu, Masatoshi Mitsuhara, Satoshi Hata, Hideharu Nakashima, Nobuhiro Tsuji, Microstructural change due to isochronal annealing in severely plastic-deformed commercial purity aluminium, Philosophical Magazine, 10.1080/14786435.2015.1021400, 95, 11, 1139-1149, 2015.04, Microstructural changes, such as the density of grain boundary (GB) and dislocation density, due to isochronal annealing in severely plastic-deformed commercial purity aluminium up to 523 K was evaluated using electrical resistivity measurements and scanning transmission electron microscopy. Eventually, the GB density decreases from about 7.2 × 106 to about 2 × 106 m-1, whilst the dislocation density decreases from an initial value of around 1.3 × 1014 m-2 down to around 4 × 1013 m-2..
30. Aira Matsugaki, Gento Aramoto, Takafumi Ninomiya, Hiroshi Sawada, Satoshi Hata, Takayoshi Nakano, Abnormal arrangement of a collagen/apatite extracellular matrix orthogonal to osteoblast alignment is constructed by a nanoscale periodic surface structure, Biomaterials, 10.1016/j.biomaterials.2014.10.025, 37, 134-143, 2015.01, Morphological and directional alteration of cells is essential for structurally appropriate construction of tissues and organs. In particular, osteoblast alignment is crucial for the realization of anisotropic bone tissue microstructure. In this article, the orientation of a collagen/apatite extracellular matrix (ECM) was established by controlling osteoblast alignment using a surface geometry with nanometer-sized periodicity induced by laser ablation. Laser irradiation induced self-organized periodic structures (laser-induced periodic surface structures; LIPSS) with a spatial period equal to the wavelength of the incident laser on the surface of biomedical alloys of Ti-6Al-4V and Co-Cr-Mo. Osteoblast orientation was successfully induced parallel to the grating structure. Notably, both the fibrous orientation of the secreted collagen matrix and the c-axis of the produced apatite crystals were orientated orthogonal to the cell direction. To the best of our knowledge, this is the first report demonstrating that bone tissue anisotropy is controllable, including the characteristic organization of a collagen/apatite composite orthogonal to the osteoblast orientation, by controlling the cell alignment using periodic surface geometry..
31. Satoshi Hata, Kazuhisa Sato, Mitsuhiro Murayama, Toshihiro Tsuchiyma, Hideharu Nakashima, An experimental protocol development of three-dimensional transmission electron microscopy methods for ferrous alloys
Towards quantitative microstructural characterization in three dimensions, ISIJ International, 10.2355/isijinternational.55.623, 55, 3, 623-631, 2015.01, The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed..
32. K. Sato, H. Miyazaki, T. Gondo, S. Miyazaki, M. Murayama, Satoshi Hata, Development of a novel straining holder for transmission electron microscopy compatible with single tilt-axis electron tomography, Microscopy (Oxford, England), 10.1093/jmicro/dfv021, 64, 5, 369-375, 2015.01, We have developed a newly designed straining specimen holder for in situ transmission electron microscopy (TEM) compatible with high-angle single tilt-axis electron tomography. The holder can deform a TEM specimen under tensile stress with the strain rate between 1.5 × 10−6 and 5.2 × 10−3 s−1. We have also confirmed that the maximum tilt angle of the specimen holder reaches ±60° with a rectangular shape aluminum specimen. The new specimen holder, termed as ‘straining and tomography holder’, will have wide range potential applications in materials science..
33. Daisuke Hirakami, Toshiyuki Manabe, Kohsaku Ushioda, Kei Noguchi, Kenichi Takai, Yoshinori Hata, Satoshi Hata, Hideharu Nakashima, Effect of aging treatment on hydrogen embrittlement of drawn pearlitic steel wire, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.101.59, 101, 1, 59-64, 2015.01, Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. As-drawn pearlitic steel wire is well known to have superior resistance to hydrogen embrittlement. The resistance to hydrogen embrittlement is clarified as being further improved by aging treatment at 100-°C and 300-°C for 10-min. of as-drawn 0.8 mass% C pearlitic steel wire with φ5.0 mm (ε=1.9). The higher the aging temperature is, the better the resistance to hydrogen embrittlement becomes. Simultaneously, the strength even increased slightly by aging treatment. The mechanism is investigated by exploiting thermal desorption analysis (TDA) and the newly developed TEM precession analysis. Aging at 100-°C led to a decrease in the hydrogen content at peak I around 100-°C in the TDA curve, which is inferred to be caused by C segregation to dislocations resulting in improvement of hydrogen embrittlement. Aging at 300-°C further improved the resistance to hydrogen embrittlement, which is presumably brought about by the local recovery of the heterogeneously deformed lamellar ferrite area together with the C segregation to dislocations. Here, the strength increased slightly by aging due to the softening factor of recovery and the hardening factor of strain aging..
34. Ken Takata, Kohsaku Ushioda, Ryutaro Akiyoshi, Ken Ichi Ikeda, Jun Takahashi, Satoshi Hata, Kenji Kaneko, Improvement of strength and elongation balance of Al-Mg-Si alloy utilizing Mg-Si cluster and its mechanism, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.J2015026, 79, 8, 391-397, 2015.01, Tensile properties of Al-Mg-Si alloy with Mg-Si clusters was compared with that withβ precipitate with the same strength. It was found that the elongation of the alloy with Mg-Si cluster was greater than the alloy with β precipitate because of high work hardening rate, in particular at large strain region. Decomposition of Mg-Si cluster into solute Mg and Si atoms during the tensile deformation test were also shown by differential scanning calorimetry (DSC). Three types of dislocation characteristics were observed from these alloys by transmission electron microscopy (TEM), homogeneous distribution of dislocation with β precipitate, cell structure with Mg and Si in solid solution, and combination of them with Mg-Si cluster. For the case of alloy with Mg-Si cluster, the yield strength was significantly increased due to the cutting mechanism. Simultaneously, the elongation was greatly improved due to the presences of decomposed solute Mg and Si atoms with plastic strain, which are inferred to prevent dynamic recovery in the later stage of tensile test. Consequently, the alloy with clusters has advantages from both alloys with precipitates and solutes, in terms of strength and elongation balance among the conventional 6000 series and 7000 series Al alloys..
35. Ryutaro Akiyoshi, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Takeshi Kasama, Ken Takata, Jun Takahashi, Kohsaku Ushioda, Kenji Kaneko, Influence of aging products on tensile deformation behavior of Al-0.62 mass%Mg-0.32 mass%Si alloy, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.J2014063, 79, 5, 273-279, 2015.01, Tensile tests and microstructural observations were carried out to investigate the influence of aging products on tensile deformation behavior of Al-0.62 mass%Mg-0.32 mass%Si alloy. Solution-treated alloys were aged to form needle-like β" precipitates or Mg-Si clusters. The aged alloy with β" precipitates showed higher yield stress than that with Mg-Si clusters. Transmission electron microscopy observations revealed that the β" precipitates pinned dislocations. It was suggested that the strengthening types of the alloy with β" precipitates were both Orowan and cutting mechanism, by estimating the Orowan stress and considering crystal structure of β" precipitates. In contrast, the aged alloys with Mg-Si clusters showed excellent performance of uniform elongation due to large work hardening compared to those of the alloy with β" precipitates. Dislocations in the alloy with Mg-Si clusters were wavy in morphology. The yield stress of the alloy with Mg-Si clusters was higher than that of the solution-treated alloy and much lower than the estimated Orowan stress. This result indicated that the cutting mechanism was the main strengthening type of the aged alloy with Mg-Si clusters, and this strengthening mechanism gave a good balance of strength and elongation..
36. R. G. Abhilash Kumar, Satoshi Hata, Ken Ichi Ikeda, K. G. Gopchandran, Luminescence dynamics and concentration quenching in Gd2-xEuxO3 nanophosphor, Ceramics International, 10.1016/j.ceramint.2015.01.051, 41, 4, 6037-6050, 2015.01, Gd2-xEuxO3 nanophosphor with enhanced luminescence has been synthesized by solution combustion method in diethylene glycol medium. The effect of Eu3+ content on the structure, morphology and luminescence dynamics has been investigated. The observed red shift in charge transfer band of the nanophosphor with increase in Eu3+content is attributed to the increase in covalency and Eu-O bond length. Excess europium content leads to reduction in intensity of photoemission as a result of concentration quenching. Transient characteristics exhibit single exponential behaviour and the fitted life time values get shortened with increase of Eu3+ content, due to increase in non-radiative transition rate. The observed quenching of luminescence in the phosphor is found to be in agreement with the energy transfer theory proposed by Dexter and Schulman and found that dipole-dipole interaction between Eu3+ ions is the key mechanism responsible for quenching. Critical energy transfer distance between Eu3+ ions in Gd2-xEuxO3 is determined to be 1.148 nm. Judd-Ofelt intensity parameters and the radiative parameters of the phosphors were evaluated from the emission spectrum to analyse the crystal field environment and the degree of covalency between the rare-earth ion and the surrounding ligands. The value of Ω2 intensity parameter confirmed the hypersensitive nature of the 5D0-7F2 transition with larger asymmetry around Eu3+ ions..
37. Hisahiro Einaga, Ryo Shiranita, Hikaru Saito, Satoshi Hata, Codeposition of colloidal platinum particles and iron chloride precursor on TiO2 for efficient catalytic oxidation of CO to CO2, Chemistry Letters, 10.1246/cl.150903, 44, 12, 1786-1788, 2015, Codeposition of metal chlorides with Pt colloidal nanoparticles on TiO2 followed by oxidation at 400 °C and reduction at 200 °C improved the activity for Pt-catalyzed CO oxidation with stoichiometric amount of O2. The highest activity was obtained when FeCl3 was used as the additive with the Fe/Pt ratio of 0.2. XAFS, X-EDS, FTIR, and catalytic studies revealed that the deposition of Fe species on the reduced Pt sites gave active sites, which exhibited CO oxidation with high efficiency..
38. Zhe Lei, Takuro Horiuchi, Iwao Sasaki, Chikara Kaido, Horibe Yochi, Satoshi Hata, Toshifumi Ogawa, Hidenori Era, Hysteresis and Domain Behaviors Analysis of High Purity Fe-(5, 6) wt% Si Alloys, Physics Procedia, 10.1016/j.phpro.2015.12.090, 75, 695-702, 2015, We investigated the improvement in magnetic properties of high-purity Fe-(5, 6) wt% Si formed by cold crucible levitation melting. The results showed that Fe-6 wt% Si alloy has a smaller coercivity than Fe-5 wt% Si. The hysteresis loss of both alloys increases linearly and slightly with maximum magnetization, and increases significantly after a certain maximum magnetization. Additionally, demagnetized domain structure and domain wall motion in both samples was studied by means of Lorentz microscopy. The results indicated that the domain wall motion of Fe-6 wt% Si can be activated in lower external fields and displaces more rapidly than Fe-5 wt% Si. Moreover, the displacement of domain walls that penetrate symmetrical grain boundaries and dislocations in Fe-6 wt% Si was analyzed. The boundaries and dislocations have no pinning effect on domain wall motion..
39. Ryuichiro Oguma, Syo Matsumura, Minoru Doi, Satoshi Hata, Keisuke Ogata, Simulations of TDGL equations for B2 type ordering with two-step phase separation in Fe-Ni-Al 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, 287-294, 2015, The present authors recently developed a time-dependent Ginzburg-Landau (TDGL) formulation for ordering processes of B2 and D03 in binary alloys, taking into account the symmetrical relationships between these ordered phases. Kinetic equations for time-evolution of order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of a mean-field free energies and interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. Micro-structures in the superalloys consist of B2 ordered domains and A2 disordered matrices in the first stage of phase separation. The second stage during a subsequent aging leads to formation of B2 domains and A2 phase regions in the former A2 matrices and B2 domains, respectively. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors have applied the TDGL formulation to this alloy system, and performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations..
40. P. S. Ghosh, A. Arya, U. D. Kulkarni, G. K. Dey, Satoshi Hata, T. Nakano, K. Hagihara, Hideharu Nakashima, Ab-initio study of long-period superstructures and anti-phase boundaries in Al-rich γ-TiAl (L10)-based alloys, Philosophical Magazine, 10.1080/14786435.2014.885135, 94, 11, 1202-1218, 2014.04, In this work, we report first-principles investigation of structural stability of all experimentally observed ordered long-period superstructures (LPSs), viz., r-Al2Ti, h-Al2Ti, Al5Ti 3 along with Al5Ti3′, Al 11Ti7 and Al3Ti2 LPSs, which are observed only as short-range ordered clusters at nanoscale level in Al-rich TiAl-based alloys. We adopt a procedure based on space-filling tiling arrangement of ordered Ti2Al, Ti3Al, Ti4Al motifs and their combination along with a symmetry analysis programme to determine the unit cell and the crystallographic information of Al 5Ti3′, Al11Ti7 and Al 3Ti2 LPSs in terms of L10 fcc unit cell. First-principles calculations are performed to further refine these crystallographic parameters (Wyckoff positions and lattice parameters) obtained from the above procedure. Moreover, it is found that the family of five LPSs have subgroup-supergroup relationships with γ-TiAl (Sp. gr. P4/mmm) and among themselves. Further, we find the inherent stability of r-Al2Ti + γ-TiAl and 2Al5Ti3 + γ-TiAl phase mixtures at 0 K compared to isomolecular Al3Ti2 and Al 11Ti7 LPSs at their respective concentrations. The calculations of single-crystal elastic constants of Al5Ti 3, Al11Ti7, Al3Ti2 and Al5Ti3′ LPSs show all these four structures are mechanically stable. We also calculate antiphase boundary (APB) formation energies for two types of APBs, viz., type-A and type-C in ordered Al 5Ti3 LPS using the supercell approach. The relaxed APB energies for type-A and type-C APBs are 15.44 and 124.16 mJ/m2, respectively..
41. R. G. Abhilash Kumar, Satoshi Hata, Ken Ichi Ikeda, K. G. Gopchandran, Influence of metal ion concentration in the glycol mediated synthesis of Gd2O3
Eu3+ nanophosphor, Ceramics International, 10.1016/j.ceramint.2013.10.020, 40, 2, 2915-2926, 2014.03, The solvothermal synthesis of highly luminescent and homogeneous Gd 2O3:Eu3+ nanophosphor using diethylene glycol as medium, followed by controlled combustion with citric acid as fuel is reported. The influence of concentrations of carboxylic acid and metal cations on the structure, morphology and luminescence properties are investigated in detail. The microscopic investigations indicate the nanocrystalline nature and the strong influence of cation concentration on the size, shape and agglomeration of the particles. It is found that increase in concentration of metal cations lead to the reduction in agglomeration of nanophosphors. The large value of intensity parameter Ω2, suggested that Eu 3+ ions reside in a more asymmetric environment, resulted in intense emission due to 5D0-7F2 electric dipole transition. Emission decay analysis of the samples exhibited one exponential nature. The samples prepared under optimum conditions showed a quantum efficiency of 78.63% and a moderately high life time of 1.217 ms..
42. Satoshi Hata, Kazuhisa Sato, Mitsuhiro Murayama, Toshihiro Tsuchiyma, Hideharu Nakashima, An experimental protocol development of three-dimensional transmission electron microscopy methods for ferrous alloys
Towards quantitative microstructural characterization in three dimensions, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.100.889, 100, 7, 889-896, 2014.01, The majority of engineering steels are ferromagnetic and structually inhomogeneous on special scales ranging from nanometers to micrometers, and physical properties of engineering steels arise from three-dimensional (3D) features of the microstructure. Thus, obtaining 3D representation with a large field of view is desired for transmission electron microscopy (TEM) based microstructure characterization to establish microstructure - physical properties relationships with reasonable statistical relevancy. Here, we venture to use a conventional sample preparation process, i.e., mechanical polishing followed by electro-polishing, and experimental protocols optimization for electron tomography (ET) for ferromagnetic materials, especially engineering steels' microstructural characterization are carried out. We found that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisition. For example, for a ferritic heat-resistant 9Cr steel with lath martensite structure, mechanically thinning down to 30 μm or thinner was necessary to acquire an adequate tilt-series image of carbide precipitates in the high-angle annular dark-field scanning TEM (HAADF-STEM) mode. On the other hand, tilt-series image acquisition from dislocation structures remains challenging because the electron beam deflection during specimen-tilt was unavoidable and significant in the HAADF-STEM mode. To overcome the electron beam deflection problem, we evaluate several relatively accessible approaches including the "Low-Mag and Lorentz" TEM/STEM modes; although they are rarely used for ET, both the modes reduce or even zero the objective lens current and likely weaken the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of those experimental components are discussed..
43. Shigeto Yamasaki, Masatoshi Mitsuhara, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Low stress creep deformation in high chromium ferritic heat-resistant steel evaluated by helicoid spring creep test method, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.100.688, 100, 5, 688-695, 2014.01, We measured a creep deformation in Grade T91 steel under low stress condition using a helicoid spring creep test method. By applying this method, we measured a very low strain rate creep deformation in a short time as there is no need to consider the contribution of the microstructural change to the creep deformation behavior. We distinguished magnitude of several types of time-dependent deformation, including viscoelastic deformation, which occurs during the creep test in order to evaluate a time-dependent plastic deformation in strain-time curves. This consideration derives a conclusion that the time-dependent plastic deformation occurs even in a short time and low stress condition. Moreover, we confrmed a strain rate of whole creep deformation is controlled by the strain rate of the time-dependent plastic deformation at the time of 270 ks in the creep test. We confrmed that though there are almost no changes in the microstructure of Grade T91 steel during creep tests, the susceptibility on strain rate to applied stress has changed depending on the applied stress region. In addition, activation energy of the creep deformation was also different in each stress region. From these results, we concluded that the dominant creep deformation mechanism is different in the low stress region and high stress region..
44. Mohammed Shahabuddin, Nasser S. Alzayed, Sangjun Oh, Seyong Choi, Minoru Maeda, Satoshi Hata, Yusuke Shimada, Md Shahriar Al Hossain, Jung Ho Kim, Microstructural and crystallographic imperfections of MgB2 superconducting wire and their correlation with the critical current density, AIP Advances, 10.1063/1.4862670, 4, 1, 2014.01, A comprehensive study of the effects of structural imperfections in MgB2 superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB2 material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB2, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB2, however, even at low sintering temperature, and thus block current transport paths..
45. Y. Hishinuma, A. Kikuchi, Y. Shimada, Satoshi Hata, T. Takeuchi, S. Yamada, A. Sagara, Effect of boron particle size on microstructure and superconducting properties of in-situ Cu addition MgB2 multifilamentary wire, Journal of Physics: Conference Series, 10.1088/1742-6596/507/2/022009, 507, PART 2, 2014, In previous studies, the secondary (impurity and non-reactive) phase and voids were observed in MgB2 matrix after the heat treatment, and then these are the lowering factors of critical current density (Jc) property. In order to improve Jc property by microstructure control of MgB2 matrix, the fine elemental boron powder as the raw material was carried out using the high-speed vibrated milling with tungsten carbide (WC) jar. The average particle size of metal boron powder was decreased from 1.14 μm to 0.20 μm by the high-speed vibrated milling. The various fine particle boron powders as the function of milling time were also prepared, and in-situ Cu addition MgB2 multifilamentary wires using these fine boron powders were fabricated. Critical transition temperature (Tc) value of Cu addition MgB2 wire using fine boron powder obtained to about 37 K. No change of the Tc property by the different particle sized boron powders was confirmed. In this paper, the comparisons of microstructure and superconducting properties between the different boron particle sizes were investigated..
46. Shigeto Yamasaki, Masatoshi Mitsuhara, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Low-stress creep deformation in long-term aged ferritic heat-resistant steel, Materials Transactions, 10.2320/matertrans.M2013427, 55, 5, 842-849, 2014, The transition of the creep deformation mechanism in the low-stress region of Grade P92 high Cr ferritic heat-resistant steel was investigated by a helicoid spring creep test. Specifically, the effect of variation in the microstructure of steel on creep deformation behavior was evaluated by subjecting samples to thermal aging for 1000, 3000, 5000, and 10000 h at 700°C over a wide stress range. In addition, stress exponents were determined from the stress dependence of the minimum strain rate in the creep curves up to 270 ks. The transition of the creep mechanism was indicated when the stress exponent decreased from 4 in the high-stress region to 1 in the low-stress region below 40 MPa. A quantitative evaluation of the microstructure of a tempered martensite sample, including the determination of the amount of dissolved Mo and W, dispersion state of the precipitates, and length of the grain boundaries per unit area, was also carried out. Furthermore, the change in the minimum strain rate was evaluated as a function of the microstructural changes that accompanied thermal aging. It was found that the change in the strain rate was the most affected by the fineness of the martensitic lath structure in the high-stress region and by the dispersion density of M23C6 precipitates in the low-stress region. Based on these results, it was concluded that the microstructural parameter that most affects creep deformation behavior differs depending on the stress region due to the difference in the creep mechanism..
47. R. G Abhilash Kumar, Satoshi Hata, K. G. Gopchandran, Diethylene glycol mediated synthesis of Gd2O3
Eu 3+ nanophosphor and its Judd-Ofelt analysis, Ceramics International, 10.1016/j.ceramint.2013.05.010, 39, 8, 9125-9136, 2013.12, Gd1.9Eu0.1O3 nanophosphor with enhanced photoemission is successfully synthesized by a controlled combustion method of metal-citrate complex in diethylene glycol medium. It is found that the phase formation and spectral properties including quantum efficiency are highly sensitive to sintering temperature and the role of citric acid both as a chelating agent and as a fuel for combustion was evident in the study. The formation of cubic Gd2O3:Eu nanocrystalline phosphor was confirmed by X-ray diffraction, Raman and Infrared measurements. Transmission electron microscopic images together with the SAED patterns indicate the formation of spherical Gd2O3 nanocrystalline powder with well defined planes separated by 0.312 nm of cubic Gd2O3. The high degrees of homogeneity observed in the electron micrographs are attributed to the glycol medium used. The intensities of transitions between different J levels depend on the symmetry of the local environment of Eu 3+ activators and are described using the Judd-Ofelt analysis. The spectral properties of the samples prepared under optimum conditions have shown large asymmetric ratio, indicating high degree of distortion in local environment around Eu3+ ions and a maximum quantum efficiency of 78% was obtained. The life-time measurements indicated an increase from 0.83 to 1.28 ms with increase in sintering temperature from 700 to 1000 C. The chromaticity and correlated colour temperature of the emission were evaluated based on the 1931 CIE chromaticity diagram. The absorptions observed in the excitation spectra show the suitability of the nanophosphor obtained in this study for getting excited in UV, NUV and visible regions for a variety of device applications..
48. Junjie Shen, Ikeda Kenichi, Satoshi Hata, Hideharu Nakashima, Instantaneous creep in face-centered cubic metals at ultralow strain rates by a high-resolution strain measurement, Journal Wuhan University of Technology, Materials Science Edition, 10.1007/s11595-013-0826-y, 28, 6, 1096-1100, 2013.12, Instantaneous creep in face-centered cubic metals, 5N Al (99.999%), 2N Al (99%) and 4N Cu (99.99%) with different grain sizes, was firstly investigated by sudden stress-change experiments at ultralow strain rates dot \varepsilon ≤ 10-10 s-1 and temperature T < 0.32 T m. The experimental results indicate that the observed instantaneous creep is strongly dependent on grain size, the concentration of impurity, and stacking fault energy. Creep in high-purity aluminum, 5N Al, with a very large grain size, d g > 1600 μm, shows non-viscous behavior, and is controlled by the recovery of dislocations in the boundary of dislocation cells. On the other hand, for 5N Al with a small grain size, d g=30 μm, and low-purity aluminum, 2N Al, with d g= 25 μm, creep shows viscous behavior and may be related to 'low temperature grain boundary sliding'. For high-purity copper, 4N Cu, with d g= 40 μm and lower stacking fault energy, creep shows a non-viscous behavior, and is controlled by the recovery process of dislocations. For all of the samples, creep shows anelastic behavior..
49. H. Matsuo, K. Ikeda, Satoshi Hata, Hideharu Nakashima, H. Yamada, C. N. Xu, Phase transformation behavior and pseudoelastic deformation in SrAl 2O4, Journal of Alloys and Compounds, 10.1016/j.jallcom.2012.04.009, 577, SUPPL. 1, 2013.11, Europium-doped strontium aluminate [SrAl2O4:Eu 2+] (SAOE) emits green light under an applied mechanical stress in a phenomenon called mechanoluminescence (ML). In order to clarify the relationship between ML and its structure, the microstructure, phase transformation behavior and structural change under a load on SAO ceramics were investigated. The microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been that SAO has a twin structure with three kinds of morphologies. The phase transformation behavior was investigated using differential scanning calorimetric (DSC) measurements and observation of the microstructures. It is indicated that the twin structures are formed by a thermoelastic martensitic transformation from a hexagonal (β) to a monoclinic (α) phase at about 670 C. In addition, the structural change under a load was observed by in situ TEM nanoindentation. It is clarified that pseudoelastic deformation occurred in SAO. These results suggest that ML occurs with rearrangement of variants of α phase. Crown.
50. Yuichiro Koizumi, Takeshi Otsuka, Yoritoshi Minamino, Takemori Takayama, Masanori Ueyama, Takeshi Daio, Satoshi Hata, Microstructures developed by super-rapid induction heating-and-quenching (SRIHQ) of Fe-1.4%Cr-1%C pearlitic steel, Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 10.1016/j.msea.2013.04.024, 577, 29-35, 2013.08, Microstructures and hardness of a Fe-1.4%Cr-1%C pearlitic steel processed by super-rapid induction heating-and-quenching (SRIHQ) under various conditions have been investigated. A nano-scaled laminated microstructure composed of two different types of martensite (highly-twinned or containing a high dislocation density) was formed and the maximum hardness was obtained by heating to 1223. K in 0.5. s and quenched. Electron energy loss spectroscopy indicated that the two different types of martensite were formed depending on the local solute-concentration in the non-uniform solute-distribution realized by the SRIHQ-process..
51. Jun Jie Shen, Kenichi Ikeda, Satoshi Hata, Hideharu Nakashima, "abnormal transient creep" in fine-grained Al-5356 alloy observed at low strain rates by high-resolution strain measurement, Transactions of Nonferrous Metals Society of China, 10.1016/S1003-6326(13)62585-6, 23, 5, 1209-1214, 2013.05, Transient creep at very low strain rates (less than 10-10s -1) is still unclear. The traditional uniaxial creep testing is less useful due to unsatisfied resolution strain ∼(10-6). To study transient creep behavior at such low strain rates, a high-resolution strain measurement using the helicoid spring specimen technique was employed in a fine-grained Al-5356 alloy at temperatures ranging from 0.47 Tm to 0.74Tm (Tm: melting point). To clarify transient creep mechanism at such low strain rates, transmission electron microscopy (TEM) was used in microstructure observation of crept specimens. The abnormal transient creep, high temperature strengthening at T>Tp(Tp: the phase transformation temperature, 0.58Tm) or intermediate temperature softening at 0.4Tmp and double-normal type (creep curves including double work-hardening stages) at T=Tp, were firstly observed. The substructure observation in a crept specimen at T=0.58Tm and É=1*10-4 shows pile-up dislocations including many small jogs with equal interval, and dislocations emitted from grain boundaries. The β-Al3Mg2 phase dissolves under the condition of testing temperatures higher than 523 K, which causes solid-solution quantity of Mg atoms to increase. Therefore, the "abnormal transient creep" may be related to the difference of solid solution strengthening caused by phase change during the creep tests..
52. P. S. Ghosh, A. Arya, U. D. Kulkarni, G. K. Dey, T. Nakano, Y. Umakoshi, K. Hagihara, Satoshi Hata, First-principles investigation of phase stability and electronic structure of tetragonal (P4/m) Ga 3-x Al x Ti 2 (x = 0-3) compounds, Philosophical Magazine Letters, 10.1080/09500839.2013.769068, 93, 5, 273-282, 2013.05, We report a first-principles study of the phase stability and electronic structure of tetragonal (P4/m) Ga3-x Al x Ti2 (x = 0-3) compounds to investigate the conspicuous absence of Al3Ti2 in the Al-Ti phase diagram while isostructural Ga3Ti2 is stable in the Ga-Ti phase diagram. It is found that Ga3Ti2 is the most stable phase compared to its ternary derivatives (Ga3-x Al x)Ti2, with the stability of Al3Ti2 being the lowest. Furthermore, the equimolecular phase mixture of γ-TiAl and r-Al2Ti is found to be more stable than Al3Ti2. By analysing the total and partial density of states, the valence charge transfer and the valence charge density distributions, we substantiate our conclusions from the perspective of the electronic structure..
53. H. Sosiati, Satoshi Hata, T. Doi, A. Matsumoto, H. Kitaguchi, Hideharu Nakashima, Nanostructure characterization of Ni and B layers as artificial pinning centers in multilayered MgB2/Ni and MgB2/B superconducting thin films, Physica C: Superconductivity and its Applications, 10.1016/j.physc.2013.02.011, 488, 1-8, 2013.05, Research on the MgB2/Ni and MgB2/B multilayer films fabricated by an electron beam (EB) evaporation technique have been extensively carried out. The critical current density, Jc of MgB2/Ni and MgB2/B multilayer films in parallel fields has been suggested to be higher than that of monolayer MgB2 film due to introducing the artificial pinning centers of nano-sized Ni and B layers. Nanostructure characterization of the artificial pinning centers in the multilayer films were examined by transmission electron microscopy (TEM) and scanning TEM (STEM-energy dispersive X-ray spectroscopy (STEM-EDS))-EDS to understand the mechanism of flux pinning. The growth of columnar MgB2 grains along the film-thickness direction was recognized in the MgB2/Ni multilayer film, but not in the MgB2/B multilayer film. Nano-sized Ni layers were present as crystalline epitaxial layers which is interpreted that Ni atoms might be incorporated into the MgB2 lattice to form (Mg,Ni)B 2 phase. On the other hand, nano-sized B layers were amorphous layers. Crystalline (Mg,Ni)B2 layers worked more effectively than amorphous B-layers, providing higher flux-pinning force that resulted in higher Jc of the MgB2/Ni multilayer film than the MgB 2/B multilayer film..
54. Ryuichiro Oguma, Syo Matsumura, Minoru Doi, Satoshi Hata, Keisuke Ogata, Application of TDGL model to B2 type ordering with two step phase separation in Fe-Ni-Al alloys, 21st International Materials Research Congress, IMRC 2012 Proceedings of the Multiscale Materials Modeling 2012 Conference, 10.1557/opl.2013.456, 1535, 41-47, 2013.01, Formation of domain structures in two-step phase separation in Fe-based Fe-Ni-Al alloys are investigated by applying a time-dependent Ginzburg-Landau (TDGL) model. The present authors recently developed a TDGL formulation for ordering processes of B2 and D03 in binary alloys, taking into account the symmetrical relationships between these ordered phases. In this formulation, multiple types of variants of the structures are represented by three order parameters which can be measured independently through crystal structure factors. Mean-field free energies are defined in a form of Landau type expansion with the order parameters and a composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations..
55. Satoshi Hata, H. Sosiati, Y. Shimada, A. Matsumoto, K. Ikeda, Hideharu Nakashima, H. Kitaguchi, H. Kumakura, Imperfection of microstructural control in MgB2 superconducting tapes fabricated using an in-situ powder-in-tube process
Toward practical applications, Journal of Materials Science, 10.1007/s10853-012-6901-5, 48, 1, 132-139, 2013.01, MgB2 is a promising superconductor for future applications to superconduct wires and tapes used at the liquid hydrogen temperature (20 K). Because the maximal superconducting current (critical current) in MgB 2 depends on its microstructure, an "in-situ" process to fabricate MgB2 based on a reaction between Mg and B is effective in controlling the microstructure. However, the critical current in the fabricated MgB2 wires and tapes is not sufficiently high for practical use. This may be attributed to the imperfectness of the microstructural control in MgB2 wires and tapes. In this paper, we will discuss the microstructural features of MgB2 tapes fabricated using a typical in-situ powder-in-tube process. By observing the early stage of microstructural evolution in detail, we can gain insights into the next strategy for improving the microstructure of MgB2 tapes with respect to their applications..
56. Takayoshi Nakano, Koji Hagihara, Satoshi Hata, Hajime Shigyo, Hideharu Nakashima, Yukichi Umakoshi, Ashok Arya, Ulhas D. Kulkarni, Long-period ordered superstructures that appear in an (Al,Ga)-rich (Al,Ga)Ti system, Philosophical Magazine, 10.1080/14786435.2012.699691, 93, 1-3, 22-37, 2013.01, Long-period ordered superstructures in an (Al,Ga)-rich (Al,Ga)Ti system composed of (Al,Ga)x Ti100-x (x = 50-65 at. %) were investigated by using melt-spun ribbons, focusing on the ordering process of the superstructural phases. Compositional regions in which h-(Al,Ga)2Ti (Ga2Zr-type), (Al,Ga)5Ti3 and (Al,Ga) 3Ti2 with threefold, fourfold and fivefold periodicity, respectively, appeared coherently in the L10 matrix were identified by electron diffraction patterns in two different temperature conditions of as-spun (a relatively high-temperature state) and heat-treatment at 700°C (a relatively low-temperature state). The (Al,Ga)5Ti3 superstructural phase always existed between the compositional region where h-(Al,Ga)2Ti and (Al,Ga)3Ti2 dominantly appear. Therefore, periodical ordering proceeds following the periodicity of the concentration wave of pure (Al,Ga) layers parallel to {310) in the Ti (002) layers from threefold to fivefold periodicity via fourfold periodicity. We found that the (Al,Ga)3Ti2 long-period superstructural phase preferentially appeared with increasing Ga concentration in the melt-spun ribbon annealed at 700°C. In other words, the h-(Al,Ga)2Ti superstructure with threefold periodicity preferentially appeared at the high temperature and a low Ga concentration. Thus, the (Al,Ga)3Ti 2-type superstructure was never produced without the addition of Ga in the present study. The long-period ordered superstructures were composed of three pairs of primitive cells, (Al,Ga)Ti2, (Al,Ga)Ti3 and (Al,Ga)Ti4, with periodic atomic arrangements corresponding to lean rhombus, fat rhombus and square, respectively. We discuss the ordering process throughout the (Al,Ga)5 superstructure based on the periodic concentration wave and exchange of atoms. The effect of long-period ordered superstructures on hardness is also mentioned..
57. Junjie Shen, Kenichi Ikeda, Satoshi Hata, Hideharu Nakashima, A new deformation region and how low do you go? - "intrinsic deformation limit", Chinese Materials Congress 2012, CMC 2012 High Performance Structure Materials, 10.4028/www.scientific.net/MSF.747-748.559, 747-748, 559-563, 2013, The creep deformation in pure aluminum was investigated using helicoid spring samples at room temperature, 298 K, and σ < 1.19 MPa. It was found that the stress exponent is n = 0, which means the creep behavior in this region is independent on applied stress but some physical properties of materials. The creep behavior was suggested to be controlled by surface diffusion based on the strongly effect of surface area on creep behavior only in this creep region (n = 0). The threshold creep rate, th ∑th, called "intrinsic deformation limit", decided by surface diffusion was suggested. This discovery provided a new perspective to understand the extremely slow deformation in the nature..
58. T. Kajihara, Y. Shimada, Satoshi Hata, K. Ikeda, Hideharu Nakashima, A. Matsumoto, T. Mochiku, H. Kitaguchi, T. Doi, Formation of Bi,Pb-2223 and microstructural evolution in Pb-Ca-Cu deposited Bi-2212(001) single crystal by heat treatment, Physics Procedia, 10.1016/j.phpro.2013.04.054, 45, 69-72, 2013, In order to study the mechanism of phase transformation from Bi-2212 to Bi-2223, we fabricated Pb-Ca-Cu deposited Bi-2212 (001) single crystals as precursors of the Bi,Pb-2223 phase. These single crystals were heated in a sintered Bi-Pb-Sr-Ca-Cu-O pellet, and microstructure was observed by analytical electron microscopy. As a result of the microstructural observation around the Bi,Pb-2223 phase, two formation paths of Bi,Pb-2223 were recognized. One is the formation from a liquid phase which is formed by Bi-2212 and melting of the secondary phases such as (Ca,Sr)2PbO4 and CuO. The other is the growth of Bi,Pb-2223 into Bi-2212 phase by diffusion of Pb, Ca and Cu atoms along the 〈hk0〉 directions of Bi-2212..
59. Yusuke Shimada, Yuuki Kubota, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Toshiya Doi, Takanori Fujiyoshi, Influences of microstructure on critical current properties in MgB 2/Al Film, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2013.2238284, 23, 3, 2013, The metal Al is lighter in weight than other substrate materials for MgB2 films such as Si and Ni. This property inspires MgB2 fabrication on a large-scale Al substrate as a new route to MgB2 tapes. Here we report microstructural factors influencing critical current density, Jc, in MgB2/Al films. MgB2/Al films were prepared by the following steps: deposit a boron layer of 3 nm in thickness on an Al substrate heated at 280°C ; deposit Mg and boron on the boron layer (sample A). For comparison, Mg and boron were deposited directly on an Al substrate heated at 265°C (sample B). The microstructure was observed by transmission electron microscopy (TEM) and scanning TEM. Jc values at 20 K in the self-field were 4.9 × 106 A cm-2 for sample A and 2.7 × 106 A cm-2 for sample B. Both the samples form an oxygen-rich layer of 10 nm in thickness at the substrate surface. This oxygen-rich layer may suppress Al diffusion into MgB2 lattices. The [001] texture of columnar MgB2 crystals grown on the substrate is stronger in sample A than in sample B. This indicates that the boron layer deposition on the Al substrate is effective for fabricating well-textured MgB2 polycrystals, resulting in the higher J c enhancement for sample A..
60. Ryuichiro Oguma, Syo Matsumura, Minoru Doi, Satoshi Hata, Keisuke Ogata, Simulations of structure formation in B2 type ordering with two step phase separation in Fe-Ni-Al alloys, 4th International Symposium on Slow Dynamics in Complex Systems: Keep Going Tohoku 4th International Symposium on Slow Dynamics in Complex Systems: Keep Going Tohoku, 10.1063/1.4794662, 1518, 703-709, 2013, The present authors recently developed a time-dependent Ginzburg-Landau (TDGL) formulation for ordering processes of B2 and D03 in binary alloys, taking into account the symmetrical relationships between these ordered phases. In this formulation, mean-field free energies are defined in a form of Landau type expansion with order parameters and a composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. Micro-structures in the super alloys consist of B2 ordered domains and A2 disordered matrices in the first stage of phase separation. The second stage during a subsequent aging leads to formation of B2 domains and A2 phase regions in the former A2 matrices and B2 domains, respectively. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors have applied the TDGL formulation to this alloy system, and performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations..
61. Akiyoshi Matsumoto, Hitoshi Kitaguchi, Toshiya Doi, Takato Kajihara, Satoshi Hata, The microstructure and superconducting properties of Bi,Pb-2223 thin film fabricated by RF sputtering and annealing method, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2012.2233856, 23, 3, 2013, We investigated the microstructures and superconducting properties of Bi,Pb-2223 thin films on SrTiO3(100) fabricated by radio-frequency (RF) sputtering and annealing. Most as-deposited films fabricated by RF sputtering did not exhibit a superconducting transition due to their low crystallinity, their deviation from the composition of Bi-2223, and their low intergrain connectivity. The as-deposited films did not contain Pb. To obtain the Bi,Pb-2223 phase, we annealed the film with Bi,Pb-2223 pellets and powder. After annealing, we confirmed that the thin film contained Pb. T c
zero = 100 K was obtained in Bi,Pb-2223 thin film after post-annealing. We observed strong 00l peaks and a sharp quadrupole in X-ray θ - 2θ and φ-scan measurements. These results suggest that this film consists of a single phase of Bi,Pb-2223 and has a biaxial orientation. The Bi,Pb-2223 thin film had a maximum Jc of 0.1 × 10 5A/cm2 at 78 K in a magnetic field of 2 T. Furthermore, Bi,Pb-2223 exhibited very strong anisotropy in its Jc-B angle characteristics..
62. J. S. Barnard, J. H. Sharp, Satoshi Hata, Masatoshi Mitsuhara, Kenji Kaneko, K. Higashida, 3-dimensional imaging of dislocation microstructures by electron beams, 2011 MRS Fall Meeting Three-Dimensional Tomography of Materials, 10.1557/opl.2012.430, 1421, 30-40, 2012.12, We review the progress in the electron tomography of dislocation microstructures in the transmission electron microscope (TEM). Dislocation contrast is visible both in conventional TEM and scanning TEM (STEM) modes and, despite the complicated intensity variations, dislocation contrast can be isolated using computational filtering techniques prior to reconstruction. We find that STEM annular dark-field (STEM-ADF) imaging offers significant advantages in terms of dislocation contrast and background artifacts. We present several examples, both in semiconducting and metallic systems, illustrating the properties of 3D dislocations. We present the high-angle triple-axis (HATA) specimen holder where the diffraction condition can be chosen at will and dislocation tomograms of multiple reflections can be combined. 3D dislocations are analyzed in terms of dislocation density and dislocation nodal structures. Several avenues of study are suggested that may exploit the 3D dislocation data..
63. Jung Ho Kim, Sangjun Oh, Yoon Uk Heo, Satoshi Hata, Hiroaki Kumakura, Akiyoshi Matsumoto, Masatoshi Mitsuhara, Seyong Choi, Yusuke Shimada, Minoru Maeda, Judith L. MacManus-Driscoll, Shi Xue Dou, Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi, NPG Asia Materials, 10.1038/am.2012.3, 4, 1, 2012.01, Increasing dissipation-free supercurrent has been the primary issue for practical application of superconducting wires. For magnesium diboride, MgB 2, carbon is known to be the most effective dopant to enhance high-field properties. However, the critical role of carbon remains elusive, and also low-field critical current density has not been improved. Here, we have undertaken malic acid doping of MgB2 and find that the microscopic origin for the enhancement of high-field properties is due to boron vacancies and associated stacking faults, as observed by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The carbon from the malic acid almost uniformly encapsulates boron, preventing boron agglomeration and reducing porosity, as observed by three-dimensional X-ray tomography. The critical current density either exceeds or matches that of niobium titanium at 4.2 K. Our findings provide atomic-level insights, which could pave the way to further enhancement of the critical current density of MgB2 up to the theoretical limit..
64. Y. Hishinuma, A. Kikuchi, K. Matsuda, K. Nishimura, Y. Kubota, Satoshi Hata, S. Yamada, T. Takeuchi, Microstructure and superconducting properties of Cu addition MgB2 multifilamentary wires using boron isotope powder as the boron source material, Physics Procedia, 10.1016/j.phpro.2012.06.119, 36, 1486-1491, 2012.01, The natural boron has two kinds of isotopes which are existed 20 wt% boron-10 (10B) and 80 wt% boron-11 (11B). 11B isotope is stable against the neutron irradiation without nuclear transformation. For an advanced fusion application, in-situ PIT process using 11B isotope powder as the boron source material was desirable to enhance low induced radio-activity of MgB2superconducting wire. We tried to fabricate the in-situ Cu addition MgB2/Ta/Cu multifilamenatry wire using boron isotope powder as the boron source material. In this study, superconductivity and microstructure of MgB2 wire using boron isotope powder were investigated. Tc value of MgB2 wire using 11B powder was shown to about 37 K by the low temperature diffusion reaction, and its value was higher than commercial natural powder. However, Jc value of MgB2 wire using 11B isotope powder was remarkably lower than that of commercial natural powder. This is caused by the forming of much impurity phase and decrease of MgB2 volume fraction due to the remaining of much non-reactive 11B isotope powder..
65. Atsushi Sho, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Effect of nitrogen on creep rupture strength and toughness after aging of an austenitic heat resistant steel, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane.98.117, 98, 4, 117-124, 2012, Creep-rupture tests and Charpy impact tests after long-term thermal aging were performed for three austenitic heat-resistant steels of which compositions were Fe-25%Ni-23.5%Cr-1%Mo-6%W-(0.11 to 0.27)%N-0.05%Ti-0.20%V-0.25%Nb-0.004%B by wt% to reveal the influence of nitrogen contents on the mechanical properties required for boiler tubes. Creep-rupture strengths of the steels at 700 °C for 6000 h were higher than 155 MPa. The material which showed the highest strength at 700 °C for 6000 h was the 0.21N steel. Nitrogen in the steels contributes to increasing the creep-rupture strength. The effect of nitrogen under higher stress condition became larger while the effect became smaller under lower stress condition. It was supposed that nitrogen decreased the effect of precipitation strengthening by stabilizing the austenite phase for a longer time while it increased the effect of solid solution strengthening. On the other hand, the Charpy impact value of all steels after aging at 700 °C for 1000 h became less than 10 J/cm2. Nitrogen in the steels did not have a notable influence on the toughness after long-term thermal aging because precipitates of M23C6 and a tungsten-rich phase formed along grain boundaries deteriorated the toughness..
66. U. D. Kulkarni, A. Arya, Satoshi Hata, Premonitory effects near critical transition temperature in ordering systems – a monte carlo simulation, Philosophical Magazine, 10.1080/14786435.2012.713136, 95, 35, 4470-4483, 2012, Premonitory effects manifest themselves in an ordering transition of the first kind (order) in the form of anomalously high short-range order (SRO) intensity at temperatures marginally above Tc, the critical transition temperature. This intensity located at the superlattice positions of the long-range ordered (LRO) phase is often attributed to the formation of ‘heterophase fluctuations’ resembling clusters of the LRO phase. Monte Carlo simulations in a hypothetical system showing FCC-to-L12 ordering transition have been carried out here to shed some light on this phenomenon and to look into the atomic configurations that make up these fluctuations. 92..
67. Takayoshi Nakano, Satoshi Hata, Koutarou Hayashi, Yukichi Umakoshi, Some long-period superstructures and the related motion of dislocations in Al-rich TiAl single crystals, 141st Annual Meeting and Exhibition, TMS 2012 TMS 2012 - 141st Annual Meeting and Exhibition, Supplemental Proceedings, 2, 797-804, 2012, Various long-period superstructures that appear in Al-rich TiAl are composed of three pairs of primitive cells, Ti 2Al, Ti 3Al, and Ti 4Al, having periodic atomic arrangements in unique shapes of lean rhombi, fat rhombi, and squares, respectively, on the (002) Ti layers. These primitive cells can produce long-period superstructures such as Al 5Ti 3, Al 3Ti 2, and h-Al 2Ti. The long-period superstructures play an important role in the operative deformation mode, configuration of dislocations, and related plastic deformation behavior in Al-rich TiAl, depending on the Al concentration. Fourfold ordinary dislocations, for example, often move as a group in the Al 5Ti 3 superstructure in the shapes of lean rhombi and squares embedded in the L1 0 matrix. In this study, the relationship between the periodic long-period superstructures and dislocation motion will be discussed from the viewpoint of anti-phase boundaries that form in each superstructure and their energies. The plastic deformation behavior in Al 5Ti 3 and h-Al 2Ti single-phase single crystals is also discussed..
68. Hosni Idrissi, Stuart Turner, Masatoshi Mitsuhara, Binjie Wang, Satoshi Hata, Michael Coulombier, Jean Pierre Raskin, Thomas Pardoen, Gustaaf Van Tendeloo, Dominique Schryvers, Point defect clusters and dislocations in FIB irradiated nanocrystalline aluminum films
An electron tomography and aberration-corrected high-resolution ADF-STEM study, Microscopy and Microanalysis, 10.1017/S143192761101213X, 17, 6, 983-990, 2011.12, Focused ion beam (FIB) induced damage in nanocrystalline Al thin films has been characterized using advanced transmission electron microscopy techniques. Electron tomography was used to analyze the three-dimensional distribution of point defect clusters induced by FIB milling, as well as their interaction with preexisting dislocations generated by internal stresses in the Al films. The atomic structure of interstitial Frank loops induced by irradiation, as well as the core structure of Frank dislocations, has been resolved with aberration-corrected high-resolution annular dark-field scanning TEM. The combination of both techniques constitutes a powerful tool for the study of the intrinsic structural properties of point defect clusters as well as the interaction of these defects with preexisting or deformation dislocations in irradiated bulk or nanostructured materials..
69. J. J. Shen, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Creep Mechanisms in a Fine-Grained Al-5356 Alloy at Low Stress and High Temperature, Materials Transactions, 10.2320/matertrans.M2011143, 52, 10, 1890-1898, 2011.11, Monotonic creep tests were carried out on fine-grained Al-5356 alloy with grain size dg = 5 ± 0. 5 mm by the helicoid spring specimen technique at homologous temperatures ranging from 0.63 to 0.74 and applied stresses of 0.13 to 1.42MPa. At stresses lower than about 0.50 MPa, Bingham-type viscous creep with activation energy Q = 80 ± 25 kJ/mol, characterized by a threshold stress which decreases with increasing temperature, was predominant. At a stress above about 0.50 MPa, grain boundary sliding with a stress exponent n = 2 and Q = 85 ± 25 kJ/mol obviously contributed to the measured creep data. Stress redistribution was evaluated, and it did not greatly influence the stress exponent. The creep mechanisms were elucidated with respect to standard creep models supported by the substructures studied by transmission electron microscopy. Viscous creep (n = 1) was identical to be Harper-Dorn creep controlled by dislocation core diffusion. The motion of jogs on edge dislocations dependent on dislocation core diffusion was observed to control the creep. Grain boundary sliding accommodated by slip with n = 2 was noted, while hardening and the recovery of dislocations at grain boundaries were suggested to control the creep. Microstructural observations along with a determination of parametric variations in the creep rates were useful for identifying the underlying deformation mechanisms..
70. H. Sosiati, Satoshi Hata, A. Matsumoto, H. Kitaguchi, H. Kumakura, Effect of ball-milling treatment on microstructure of in situ powder-in-tube (PIT) MgB2 tape, AIP Conference Proceedings, 10.1063/1.4730732, 1454, 246-250, 2011.11, In an in situ powder-in-tube (PIT) fabrication of MgB2 superconducting tapes, it has been found that ballmilling treatment on a starting powder is effective for improving critical current density (Jc) of the MgB2 tapes. In the present study, microstructures/nanostructures of MgB2 tapes and the mechanism of the Jc enhancement by the ball milling treatment were investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. A mixed powder of Mg and amorphous B was ball milled for 4 h. The milled powder was packed in a pure Fe tube and then cold rolled into a tape specimen. A heat treatment was performed at 600 C for 1 h under an Ar atmosphere and subsequently furnace cooled. MgB2 tape specimens without the ball-milling treatment were also prepared for comparison. A focused ion beam (FIB)-microsampling technique was used for TEM specimen preparation. The MgB2 tape with the ball-milling treatment exhibited a dense and uniform microstructure mainly composed of nano-crystalline MgB2. On the other hand, MgB2 tapes without the ball-milling treatment showed inhomogeneous microstructures that comprise of a porous uncrystallized area and a crystallized one. It was also found that the averaged grain size of the nano-crystalline MgB2 becomes smaller by the ball-milling treatment. Thus, it can be explained that the Jc enhancement by the ball-milling treatment is owing to improvements in the grain connectivity and microstructural uniformity of the crystalline MgB2 phase in the tape..
71. Y. Shimada, Y. Kubota, Satoshi Hata, K. Ikeda, Hideharu Nakashima, A. Matsumoto, K. Togano, H. Kumakura, Electron microscopy observations of MgB2 wire prepared by an internal Mg diffusion method, Physica C: Superconductivity and its Applications, 10.1016/j.physc.2011.05.143, 471, 21-22, 1137-1141, 2011.11, Microstructure in a high-density MgB2 wire fabricated by an internal Mg diffusion (IMD) process has been investigated by electron microscopy imaging and analysis at different scales. In the IMD process, a pure Mg rod was used as Mg source, and nanosized SiC powders were mixed with amorphous B powders. In the case of a heat treatment at 640 °C for 1 h carried out after rolling and drawing processes, the wire has two microstructural features that degrade critical current density: uncrystallized zones composed mainly of unreacted B and SiC powders, and cracks partly filled with course Mg 2Si crystals. Those cracks were formed in the uncrystallized zones as well as in crystallized MgB2 zones. It indicate that the cracks formed by the mechanical milling and drawing remain after the heat treatment..
72. Junjie Shen, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Transient creep in high-purity aluminum at ultra-low strain rate and room temperature by constant stress and changing-stress experiments, Materials Transactions, 10.2320/matertrans.M2011175, 52, 10, 1885-1889, 2011.11, Creep of high-purity aluminum (5N Al) at room temperature and ultra-low strain rate was investigated by a high sensitive helicoid-spring specimen technique under conditions of constant and changing stress. Creep deformation consists of transient creep stages, and no secondary creep stage was observed. Li's equation showed a good fit to the experimental curves. During nominal steady-state creep, the stress exponent is equal to one regardless of initial state of specimens. However, the nominal steady-state creep rate for water quenched 5N Al is one order less than that for the static recovered specimens due to work hardening. With increase in stress, creep strengthening (the creep rate progressively decreasing in subsequent segments) was observed, which is due to different hardening remains because changing-stress creep experiment was conducted in the transient creep stage. Those phenomena of work hardening indicate creep deformation is controlled by recovery and work-hardening mechanism. During transient creep, every decrease in stress is associated with the large and long anelastic backflow. The anelastic transient strain for stress reduction is equivalent to elastic deformation corresponding to the applied stress, while transient strain is 2.5 times greater than the equivalent elastic deformation regardless of whether stress increases or is constant. The transient effect was suggested to be due to a mix of anelastic behavior caused by the internal redistribution of stress and inelastic behavior..
73. U. D. Kulkarni, Satoshi Hata, T. Nakano, Masatoshi Mitsuhara, K. Ikeda, Hideharu Nakashima, Monte Carlo simulation of antiphase boundaries and growth of antiphase domains in Al5Ti3 phase in Al-rich -TiAl intermetallics, Philosophical Magazine, 10.1080/14786435.2011.563761, 91, 22, 3068-3078, 2011.08, Predominantly two kinds of antiphase boundaries (APBs) form in Al5Ti3, which is an Al-rich ordered derivative of the -TiAl (L10) phase. This phase can be viewed as a periodic arrangement of lean rhombs and squares on the Ti-rich (002) planes of the tetragonal L10. Energies of the two types of APBs were varied in a Monte Carlo simulation by suitably changing the pair interaction parameters. APBs of both types form boundaries of Al5Ti3 antiphase domains (APDs), which coarsen with time. An important observation in this regard is that mostly facetted APBs form at lower ageing temperatures, whereas curved APBs appear to form at relatively higher ageing temperatures. The findings of this work suggest that there exists a critical temperature, akin to the roughening transition temperature for crystals, that marks the transition from facetted to curved APBs..
74. Satoshi Hata, H. Miyazaki, S. Miyazaki, Masatoshi Mitsuhara, Masaki Tanaka, Kenji Kaneko, K. Higashida, K. Ikeda, Hideharu Nakashima, Syo Matsumura, J. S. Barnard, J. H. Sharp, P. A. Midgley, High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy, Ultramicroscopy, 10.1016/j.ultramic.2011.03.021, 111, 8, 1168-1175, 2011.07, Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils..
75. Junjie Shen, Shigeto Yamasaki, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Low-temperature creep at ultra-low strain rates in pure aluminum studied by a helicoid spring specimen technique, Materials Transactions, 10.2320/matertrans.M2010405, 52, 7, 1381-1387, 2011.07, The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, ε̇, lower than 10-10 s-1 and low temperature ranging from 0.32Tm to 0.43T m. It was found that the creep behavior in this region depends strongly on grain sizes and impurity concentrations. For high-purity aluminum (5 N Al) with an average grain size, dg > 1600 μm, nearly the wire diameter of the spring sample, where the role of grain boundary during creep deformation can be negligible, the stress exponent was n ∼ 5 and the activation energy was Qc = 32 kJ/mol. Microstructural observation showed the formation of large dislocation cells (∼10μm) and tangled dislocations at the cell walls. For high-purity aluminum (5N Al) with d g = 24 μm, the stress exponent was n ∼ 1 and the activation energy was Qc = 15kJ/mol. On the other hand, for commercial low-purity aluminum (2 N Al) with dg = 25 μm, the stress exponent was n = 2 and the activation energy was Qc = 25 kJ/mol. Microstructural observations revealed dislocations emitted from grain boundaries, those dislocations interacting with intragranular dislocations and the formation of dislocation cells in the grains. Based on those experimental results, the low-temperature creep mechanisms in pure aluminum at ε̇ < 10-10 s-l have been discussed..
76. Yusuke Shimada, Yuuki Kubota, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Akiyoshi Matsumoto, Kazumasa Togano, Jahmahn Hur, Hiroaki Kumakura, Microstructure in high-density MgB2 wires prepared by an internal Mg diffusion method, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2010.2091097, 21, 3 PART 3, 2668-2671, 2011.06, Several reaction-induced diffusion processes to fabricate high-density MgB2 materials are developed, and the critical current density (Jc) has been notably enhanced. In this study, microstructure in high-density MgB2 wires fabricated by an internal Mg diffusion (IMD) process has been investigated. The inner reacted region of the wire heat-treated at 640 °C for 1 h shows dense polycrystalline MgB2 of 20-200 nm in grain sizes. Fine MgO and Mg2Si particles of 10-30 nm in sizes are dispersed in this region. On the other hand, the outer region near the Ta sheath is composed of unreacted B and SiC powders, fine MgO particles and small voids. Sizes of voids in the IMD MgB2 wire are small compared with the PIT MgB2 wire. Oxidation of Mg in the IMD process forms fine dispersion of MgO which may be effective for flux pinning..
77. H. Gao, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Dong Wang, Hiroshi Nakashima, Measurement of strain and strain relaxation in free-standing Si membranes by convergent beam electron diffraction and finite element method, Acta Materialia, 10.1016/j.actamat.2011.01.031, 59, 7, 2882-2890, 2011.04, Bridge-shaped free-standing Si membranes (FSSM), strained by low-pressure (LP) SixNy, plasma-enhanced (PE) SixN y and SixGe1-x stressors, were measured by convergent beam electron diffraction (CBED) and the finite element method (FEM). The results of CBED show that, while the strain along the length of the FSSM is compressive in an LPSixNy/Si sample, those along the length of the FSSM are tensile in PESixNy/Si and SixGe1-x/Si samples. The average absolute values of strains are different in FSSM with LPSixNy, PESixNy and SixGe1-x as stressors. The FEM was used to compensate the results of CBED taking into account the strain relaxation in transmission electron microscopy (TEM) sample preparation. The FEM results give the strain properties in three dimensions, and are in good agreement with the results of CBED. There is approximately no strain relaxation along the length of FSSM, and the elastic strains along the other two axes in FSSM are partially relaxed by thinning down for the preparation of TEM samples..
78. J. J. Shen, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Room Temperature Creep and Substructure Formation in Pure Aluminum at Ultra-Low Strain Rates, Supplemental Proceedings: Materials Fabrication, Properties, Characterization, and Modeling, 10.1002/9781118062142.ch70, 2, 585-592, 2011.04, The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, ε, lower than 10-10 s-1 and room temperature, 298 K. It was found that the creep behavior at the very low ε depends strongly on grain sizes and impurity concentrations: in highpurity aluminum (5 N Al) with an average grain size of 24 μm, the stress exponent was n ~ 1; while, when the average grain size was larger than 1600 μm, the stress exponent was n ~ 5. Microstructural observation shows the formation of large dislocation cells, 10 μm. On the other hand, in commercial low-purity aluminum (2 N Al) with the average grain size of 25 μm, the stress exponent was n = 2. Microstructural observations revealed dislocations emitted from grain boundaries and the formation of lattice dislocation cells. To evaluate creep deformation mechanisms of the pure aluminum, stress change tests were conducted during creep tests. It was revealed that the deformation in the range of the stress exponent, n ~ 5, was controlled by recovery driven by internal stress, σi, because instantaneous strains at stress increment were larger than that at stress reduction. While the deformation behaviors in the ranges of the stress exponents, n ~ 1 and n = 2, were in viscous manner, because instantaneous strains at stress increment and reduction were in the same level. Based on those experimental results, the creep mechanisms have been discussed..
79. J. J. Shen, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Room temperature creep and substructure formation in pure aluminum at ultra-low strain rates, TMS 2011 - 140th Annual Meeting and Exhibition TMS 2011 - 140th Annual Meeting and Exhibition, Supplemental Proceedings, 2, 585-592, 2011, The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, ε, lower than 10-10 s -1 and room temperature, 298 K. It was found that the creep behavior at the very low ε depends strongly on grain sizes and impurity concentrations: in high-purity aluminum (5 N Al) with an average grain size of 24 μm, the stress exponent was n ∼ 1; while, when the average grain size was larger than 1600 μm, the stress exponent was n ∼ 5. Microstructural observation shows the formation of large dislocation cells, 10 μm. On the other hand, in commercial low-purity aluminum (2 N Al) with the average grain size of 25 μm, the stress exponent was n = 2. Microstructural observations revealed dislocations emitted from grain boundaries and the formation of lattice dislocation cells. To evaluate creep deformation mechanisms of the pure aluminum, stress change tests were conducted during creep tests. It was revealed that the deformation in the range of the stress exponent, n ∼ 5, was controlled by recovery driven by internal stress, σi, because instantaneous strains at stress increment were larger than that at stress reduction. While the deformation behaviors in the ranges of the stress exponents, n ∼ 1 and n = 2, were in viscous manner, because instantaneous strains at stress increment and reduction were in the same level. Based on those experimental results, the creep mechanisms have been discussed..
80. Yoji Miyajima, Masatoshi Mitsuhara, Satoshi Hata, Hideharu Nakashima, Nobuhiro Tsuji, Quantification of internal dislocation density using scanning transmission electron microscopy in ultrafine grained pure aluminium fabricated by severe plastic deformation, Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 10.1016/j.msea.2010.09.058, 528, 2, 776-779, 2010.12, Dislocation density within ultrafine grains in severely deformed aluminium was evaluated by the scanning transmission electron microscopy. The values were around 1014m-2 in commercial pure aluminium samples with equivalent strain up to 10. The obtained dislocation densities values correspond to strength between 55MPa and 70MPa according to the Bailey-Hirsch relationship..
81. Yoji Miyajima, Shin Ya Komatsu, Masatoshi Mitsuhara, Satoshi Hata, Hideharu Nakashima, Nobuhiro Tsuji, Change in electrical resistivity of commercial purity aluminium severely plastic deformed, Philosophical Magazine, 10.1080/14786435.2010.510453, 90, 34, 4475-4488, 2010.11, Commercial purity aluminium sheets were severely plastic deformed by accumulative roll bonding (ARB). Changes in electrical resistivity at 77 K and microstructure during the ARB process were traced up to 12 cycles, which corresponded to an equivalent strain of 10. The resistivity at 77 K increased with increasing number of ARB cycles, then saturated after about the sixth ARB cycle with a maximum increment of resistivity from starting material of about 1.1 n m. Since lattice defects affect the resistivity of metals, the internal dislocation density and the density of grain boundaries were evaluated from scanning transmission electron microscopy images using Ham's method and grain boundary maps obtained from electron back-scattering diffraction, respectively. The relationship between the change in resistivity and the lattice defects is discussed..
82. U. D. Kulkarni, Satoshi Hata, Masatoshi Mitsuhara, K. Ikeda, Ordering transformations in Ni75Mo15Mn10 alloy, Transactions of the Indian Institute of Metals, 10.1007/s12666-010-0125-7, 63, 5, 819-822, 2010.10, Effect of partial substitution of Mo in Ni3Mo by Mn on its ordering behaviour is studied here using Transmission Electron Microscopy (TEM). The change in alloy composition does not change the nature of the short range ordered (SRO) state, which shows intensity maxima at {1 1/2 0} and equivalent positions. However, prolonged aging at 973 K leads to transformation of the Ni75Mo15Mn10 alloy, studied here, almost entirely into the ordered D022 phase unlike in the case of the binary Ni-Mo alloy. Curved antiphase boundaries (APBs), with wetting of the interdomain D022 regions by the disordered phase, characterize the microstructure of the aged alloy. A small volume fraction of a sigma-like topologically close packed (TCP) phase that appears in the as quenched alloy seems to remain unaffected by ageing..
83. Hongye Gao, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Dong Wang, Hiroshi Nakashima, Measurement of strain in freestanding Si/SixNy membrane by convergent beam electron diffraction and finite element method, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.1143/JJAP.49.090208, 49, 9 PART 1, 2010.09, Strain in a bridge-shaped freestanding Si membrane (FSSM) induced by depositing an amorphous SixNy layer was measured by convergentbeam electron diffraction (CBED) and the finite element method (FEM). CBED results show that the strain magnitude depends negatively on the FSSM thickness, and compressive strain along the length of the FSSM is increased by approximately 0.1% at the end of the FSSM. FEM is used as a supplementary method to CBED for calculating the strain relaxation in three-dimension in the FSSM..
84. Hongye Gao, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Dong Wang, Hiroshi Nakashima, Microstructure and strain distribution in freestanding Si membrane strained by SixNy deposition, Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 10.1016/j.msea.2010.07.004, 527, 24-25, 6633-6637, 2010.09, Strain in a bridge-shaped freestanding Si membrane (FSSM) induced by depositing an amorphous SixNy layer was measured by convergent-beam electron diffraction (CBED). CBED results show that the strain magnitude depends negatively on the FSSM thickness. FEM is a supplement of the result of CBED due to the relaxation of TEM samples during fabricating. The FEM analysis results ascertain the strain property in three dimensions, and show that the strain magnitude depends negatively on the length of FSSM, and the magnitude of the compressive strain in FSSM increases as the position is closer to the upper Si/SixNy interface..
85. Hongye Gao, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Dong Wang, Hiroshi Nakashima, Strain distribution in freestanding Si/SixNy membranes studied by transmission electron microscopy, Thin Solid Films, 10.1016/j.tsf.2010.06.023, 518, 23, 6787-6791, 2010.09, Strain was induced in a bridge-shaped freestanding Si membrane (FSSM) by depositing an amorphous SixNy layer to surround the Si membrane. Convergent beam electron diffraction revealed that compressive strain is distributed uniformly along the horizontal direction in SixN y-deposited FSSM. On the other hand, strain decreases to almost zero at the ends of the FSSM, where the SixNy layer beneath the Si layer is replaced by a SiO2 buried oxide layer..
86. K. Hagihara, T. Nakano, Satoshi Hata, O. Zhu, Y. Umakoshi, Improvement of aligned lamellar structure by Cr-addition to NbSi2/MoSi2 duplex-silicide crystals, Scripta Materialia, 10.1016/j.scriptamat.2010.01.002, 62, 8, 613-616, 2010.04, The addition of Cr to (Mo0.85Nb0.15)Si2 crystals significantly improves the thermal stability of the lamellar structure composed of C11b-MoSi2 and C40-NbSi2 phases. Analysis using electron microscopy indicates the segregation of Cr atoms at the C40/C11b lamellar interface. This leads to a decrease in the lattice misfit strain at the interface and better thermal stability of the lamellae..
87. H. Matsuo, Masatoshi Mitsuhara, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Electron microscopy analysis for crack propagation behavior of alumina, International Journal of Fatigue, 10.1016/j.ijfatigue.2009.06.006, 32, 3, 592-598, 2010.03, In order to clarify crack propagation behavior of alumina (α-Al2O3), intergranular and transgranular fractures of alumina were investigated by electron microscopy techniques. For the intergranular fractures cracked grain boundaries were investigated by scanning electron microscopic electron back-scattered diffraction (SEM-EBSD) analysis. It was revealed that the intergranular fracture behavior of polycrystalline alumina with random distribution of crystallographic orientations is independent on grain boundary characters. For the transgranular fractures, fracture surfaces formed in a single-crystalline alumina were observed by electron tomography combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and high resolution TEM (HR-TEM). Three kinds of fracture surfaces were observed: even fracture surfaces, even fracture surfaces with step-terraces and fracture surfaces composed of the even fracture surface and the curved one. The even fracture surfaces mostly consist of cleavage planes parallel to {1 over(1, ̄) 0 2} and {1 over(1, ̄) 0 4}. On the other hand, the even fracture surfaces with step-terraces consist of the cleavage planes and basal planes (0 0 0 1). For the fracture surfaces composed of the even fracture surface and the curved one, both the even and curved shapes the even parts were formed by the fine cleavage planes and basal planes, whose intervals were inhomogeneous. It was indicated that the fracture surfaces in alumina are composed of the cleavage planes or basal plane at an atomic scale..
88. Y. Koizumi, T. Fujita, Y. Minamino, Satoshi Hata, Effects of plastic deformation on lamellar structure formation in Ti-39 at.% Al single crystals, Acta Materialia, 10.1016/j.actamat.2009.10.027, 58, 3, 1104-1115, 2010.02, The effects of plastic deformation on lamellar structure formation in solution-treated Ti-39 at.% Al single crystals were investigated, focusing on the role of dislocations of different slip systems. The dislocations were introduced by indentation on the surfaces of solution-treated single crystals with different crystallographic orientations. Traces of basal and prism slips were observed, depending on the position relative to the indentation. During annealing at α2 + γ dual-phase temperatures, lamellar structures were formed faster where basal slip had occurred than where prism slip had occurred. After long annealing, the length scale of lamellar structures formed depends on the slip system operated during prior deformation: in the region where only one of either basal or prism slip had occurred the lamellar structure was coarser than in undeformed crystal, while in the region where both basal and prism slips occurred the lamellar structure was finer than those formed in undeformed crystal. The reasons for the differences in lamellar structures are discussed on the basis of the frequencies of stacking fault formation on (0 0 0 1) planes as precursors to γ-precipitates. The results suggest that the cross-slip of dislocations between basal and prism planes, which gives rise to the formation of multiple stacking faults on many parallel (0 0 0 1) planes, is responsible for the refinement of lamellar structures..
89. Hajime Matsuo, Yusuke Kaieda, Nobuhiro Kojima, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Stress intensity factor and crack propagation behavior of thin α-alumina, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.74.24, 74, 1, 24-29, 2010.01, This paper reports the mechanical property and crack propagation behavior of thin ceramics. A method to evaluate the stress intensity factor, K I, of thin ceramics was proposed. Dependence of KI values on the average grain size, d, of thin α-alumina were measured by the method. KI values of thin α-alumina decreased with increasing d values from 4.3 μm to 15.2 μm, while the KI values were almost constant for 15.2 μm ≤d≤63.0 μm. The trend of KI values agreed with the dependence of fracture toughness, Kc, of bulk α-alumina. The thin α-alumina specimens after crack propagation were investigated by scanning electron microscopic electron back-scattered diffraction (SEM/EBSD) analysis. Branched cracks were hardly observed, regardless of grain size. The result indicates that the toughing mechanism do not occur in the thin α-alumina. Dependence of the transgranular fracture rate, F, and the crack deflection rate, D, on d were measured from the orientation distribution maps. However, the F values and the D values were independent of d and approximately constant. The F values and D values depend on d in bulk α-alumina. It indicates that the crack propagation behavior is varied by thinning α-alumina..
90. S. Sadamatsu, Masaki Tanaka, K. Higashida, Kenji Kaneko, Masatoshi Mitsuhara, Satoshi Hata, M. Honda, Crack tip dislocations observed by combining scanning transmission electron microscopy and computed tomography, 6th International Conference on Processing and Manufacturing of Advanced Materials - THERMEC'2009 THERMEC 2009 Supplement, 10.4028/www.scientific.net/AMR.89-91.473, 89-91, 473-478, 2010, Crack tip dislocations and dislocations introduced by three point-bending tests at high temperature are observed by combinating scanning transmission electron microscopy and computed tomography (STEM-CT). Commercially available P type (001) single crystal silicon wafers were employed. A series of STEM image was acquired from -60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. Reconstructed images of dislocations revealed dislocation structures in three-dimension..
91. Electron Tomography to Visualise Dislocations in Three-dimension.
92. Three-dimensional Visualization of Dislocations Using Two Diffraction Conditions.
93. K. Yamada, Masatoshi Mitsuhara, Satoshi Hata, Y. Miyanaga, Ryo Teranishi, N. Mori, Masashi Mukaida, Kenji Kaneko, Three-dimensional observation of microstructures in Y123 films fabricated by TFA-MOD method, Physica C: Superconductivity and its Applications, 10.1016/j.physc.2009.05.059, 469, 15-20, 1446-1449, 2009.10, We were successful for three-dimensional imaging of microstructures in YBa2Cu3O7-y (Y123) films fabricated by metal organic deposition using trifluoroacetates (TFA-MOD) method. We have reported previously, that a transmission electron microscopy (TEM) analysis clarified microstructures such as Y123 crystal grains and pores in the Y123 films. In order to derive important parameters for enhancement of superconducting properties of the Y123 films, quantitative analyses of those microstructures are required. Then, control of both pores and a-axis oriented grains distribution in the Y123 films are important. However, general TEM images provide only a two-dimensional projection of a three-dimensional object. An electron tomography is an effective technique for three-dimensional structure analysis of various materials. Cross-sectional view specimen for the three-dimensional electron tomography was prepared by focused ion-beam milling equipped with micro-sampling system. A scanning transmission electron microscopy - annular dark field technique was used for the present three-dimensional electron tomography. For the cross-sectional specimen of fired Y123 films, three-dimensional shapes and distributions of both pores and unreacted phases were observed in reconstructed images. Also, morphologies of the Y123 film surface were clearly seen..
94. Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashevia, Research on the formation behavior of recrystallization texture of high purity aluminum foil, Keikinzoku/Journal of Japan Institute of Light Metals, 59, 7, 412-415, 2009.07.
95. Yutaka Tsukano, Toshiya Doi, Hiroki Yamashita, Akira Tanaka, Ikumi Iwasaki, Yoshinori Hakuraku, Hitoshi Kitaguchi, Ken Ichiro Takahashi, Harini Sosiati, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Fabrication of Multilayered MgB2/Ni Thin Films and Their Flux Pinning Properties, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2009.2018527, 19, 3, 2807-2810, 2009.06, We prepared the multilayered MgB2 /Ni thin films with the Ni layer spacings of 32, 23 and 16 nm. The MgB2/Ni multilayer nanostructure was confirmed to be obtained from the scanning transmission electron microscope observation. The clear enhancement of Jc was observed in the multilayered MgB2/Ni thin film when the magnetic field was applied parallel to the film surface. Moreover, the peak position of FP - B curves shifted to higher magnetic field with decreasing the Ni layer spacing..
96. Masahiro Ishibashi, Kensuke Fujimoto, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, High temperature deformation behavior of sn-based solder alloys under low stress conditions by a helical spring creep testing method, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.73.373, 73, 5, 373-380, 2009.05, In the field of electronics, it is crucial to guarantee long-term joint reliability of the Sn-Ag-Cu solder alloy. Creep tests in low-stresses are necessary to guarantee the reliability. However, a very long period of time is required for the creep tests. To decide a steady-state creep strain rate, an approximate equation of a creep curve was newly applied to the helical spring creep test known as a method of a low-stress creep test. Obtained results are as follows. (1) The torsional strain component is decreased with the deformation of the helical spring shaped specimen. Therefore, the steady-state creep rate cannot be detected in the helical spring creep test. The approximate equation of a creep curve introduced by Li's group was found to be effective to obtain the steady-state creep rate for Sn-based solder alloy. (2) The helical spring creep testing method that uses the torsional deformation of the test specimen is more effective for the Sn-based solder alloy with a strong anisotropy of strength than the uniaxis creep testing method. (3) In the heat-treated Sn-3.0 mass%Ag-0.5 mass%Cu solder alloy, the creep stress exponent changed from 19 into 1.1 on the boundary of about 14 MPa. This result implies that the creep deformation mechanism was changed from the dislocation creep with dispersion-strengthening to the grain boundary sliding. This phenomenon was found for the first time by using the helical spring creep testing method..
97. H. Matsuo, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Stress-induced phase transformation in the vicinity of Vickers indentations in 10mol% CeO2 doped tetragonal ZrO2 polycrystal, 12th International Conference on Martensitic Transformations, ICOMAT-08 Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08, 167-172, 2009, The stress-induced martensitic phase transformation from a tetragonal (t) phase to a monoclinic (m) phase in a CeO2 doped tetragonal polycrystal (Ce-TZP) was investigated from the view pints of characters of lattice correspondences (LCs) between tand m-phases and morphology of m-phase. Electron back scattering diffraction (EBSD) analysis in the vicinity of Vickers indentations in Ce-TZP reveled that there were three LCs, named LCA (type A), LCB (type B) and LCC (type C), where fractions of the three LCs were 12%, 8% and 80%, respectively. Morphology of m-phase showing each of the three LCs were observed by transmission electron microscopy (TEM). A single variant of mphase with lamellar plate-shaped morphology (m-plates) was formed near the Vickers indentations. In contrast, two variants of m-phases with twin relationships (m-twins) were formed far from the Vickers indentations. The infinitesimal-deformation theory was adopted to calculate scalar magnitude of internal stress within the m-plates and m-twins for each type of the LCs. Irrespective of morphology of the m-phase, the internal stress field for type C is a tensile stress field. Regardless of the type of LCs, absolute values of internal stress in the m-plates are higher than those in the mtwins..
98. Masaki Tanaka, Masaki Honda, Masatoshi Mitsuhara, Satoshi Hata, Kenji Kaneko, Kenji Higashida, Erratum
Three-dimensional observation of dislocations by electron tomography in a silicon crystal (Materials Transactions (2008) 49:9 (1953-1956)), Materials Transactions, 10.2320/matertrans.E2008002, 49, 11, 2753, 2008.11.
99. Three-Dimensional Imaging of Crystalline Microstructures Using Electron Tomography.
100. Masaki Tanaka, Kenji Higashida, Kenji Kaneko, Satoshi Hata, Masatoshi Mitsuhara, Crack tip dislocations revealed by electron tomography in silicon single crystal, Scripta Materialia, 10.1016/j.scriptamat.2008.06.042, 59, 8, 901-904, 2008.10, Crack tip dislocations in silicon single crystals have been observed by a combination of annular dark-field scanning transmission electron microscopy and computed tomography. A series of images was acquired by maintaining the diffraction vector parallel to that of crack propagation to achieve sharp images of the dislocations. The observed dislocations were reconstructed by a filtered back-projection, and exhibited three-dimensional configurations of overlaid dislocations around the crack tip..
101. Masaki Tanaka, Masaki Honda, Masatoshi Mitsuhara, Satoshi Hata, Kenji Kaneko, Kenji Higashida, Three-dimensional observation of dislocations by electron tomography in a silicon crystal, Materials Transactions, 10.2320/matertrans.MAW200828, 49, 9, 1953-1956, 2008.09, Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from -60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. The observed dislocations were reconstructed by simultaneous interactive reconstruction technique, exhibiting a 3-D configuration of dislocations introduced by the three-point bending..
102. Satoshi Hata, T. Nakano, N. Kuwano, Masaru Itakura, Syo Matsumura, Y. Umakoshi, Microscopic properties of long-period ordering in Al-Rich TiAl alloys, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-007-9397-x, 39, 7, 1610-1617, 2008.07, The ordering mechanism of long-period superstructures (LPSs) in Al-rich TiAl alloys has been investigated by high-resolution transmission electron microscopy (HRTEM). The LPSs are classified in terms of arrangements of base clusters with different shapes and compositions formed in Ti-rich (002) layers of L 10-TiAl matrix: square Ti4Al, fat rhombus Ti3Al, and lean rhombus Ti2Al type clusters. The HRTEM observations revealed that antiphase boundaries of long-range-ordered LPS domains and short-range-ordered microdomains are constructed by various space-filling arrangements of the base clusters. Such a microscopic property characterized by the base clusters and their arrangements is markedly analogous to that of the 〈1,1/2,0〉* special-point ordering alloys such as Ni-Mo..
103. Satoshi Hata, Kosuke Kimura, Hongye Gao, Syo Matsumura, Minoru Doi, Tomokazu Moritani, Jonathan S. Barnard, Jenna R. Tong, Jo H. Sharp, Paul A. Midgley, Electron tomography imaging and analysis of γ′ and γ domains in Ni-based superalloys, Advanced Materials, 10.1002/adma.200702461, 20, 10, 1905-1909, 2008.05, A study was conducted to perform 3D microstructural analysis based on electron tomography. The study also attempted to investigate a unique domain structure in a Ni-Al-Ti alloy. A two-phase microstructure,composed of L1 2-ordered γ domains with cuboidal shape and an A1-disordered γ matrix exhibited secondary phase separation during aging precipitation of fine γ in each domain. A variety of precipitation behaviors and microstructural evolutions were observed in the second stage of phase separation, depending on on the alloy composition. The study also demonstrated tomographic DFTEM and EFTEM observations, to clarify the 3D morphology of the γ precipitates and compositional distribution in the phase-separated microstructure..
104. N. Yuzuriha, H. Sosiati, Satoshi Hata, N. Kuwano, H. Yamada, N. Uchiyama, A. Matsumoto, H. Kitaguchi, H. Kumakura, Transmission electron microscopy analysis of C4H 4S-doped MgB2 tapes, Journal of Physics: Conference Series, 10.1088/1742-6596/97/1/012277, 97, 1, 2008.02, It has been reported that doping with aromatic hydrocarbons in an in situ powder-intube fabrication process of MgB2 tapes is effective for increasing the critical current density (Jc) under magnetic fields. In this study, the mechanism of the Jc enhancement by doping with C4H4S was investigated by transmission electron microscopy (TEM). The C4H4S-doped MgB2 tape has a denser cross-sectional microstructure than that of a non-doped MgB2 tape. Electron diffraction and dark-field TEM observation indicated that the grains of MgB2 are well crystallized and slightly increase in size with the C4H4S doping. X-ray diffraction and twodimensional elemental mapping using characteristic x-rays suggested that C atoms substitute part of B atoms in MgB2 crystals. Unlike other kinds of impurity doping, such as SiC-doping, there were few nanosized inclusions formed by C 4H4S doping. Thus, it is concluded that the Jc enhancement with the C4H4S doping is due to (i) increasing supercurrent and magnetic-flux pinning at grain boundaries by the formation of dense and well-crystallized MgB2 matrix and (ii) increasing the upper critical field by the formation of Mg(B,C)2..
105. H. Matsuo, Masatoshi Mitsuhara, K. Ikeda, Satoshi Hata, Hideharu Nakashima, Electron microscopy analysis of crack propagation behavior of alumina, Materials Science and Technology Conference and Exhibition, MS and T'08 Materials Science and Technology Conference and Exhibition MS and T'08, 2, 753-761, 2008, Macroscopic features of crack propagation behavior in polycrystalline alumina (poly-alumina) and alumina single crystals (single-alumina) were analyzed by scanning electron microscopic electron back-scattered diffraction (SEM-EBSD) analysis. It was revealed that the intergranular fracture behavior is independent on grain boundary characters. When the cracks are propagated in the grains of poly- or single-alumina, zigzag cracks were produced. The zigzag cracks are composed of fracture surfaces formed along the cleavage planes. Microscopic features of fracture surfaces formed in a single-alumina were observed in detail by electron tomography combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It was by visualized that the zigzag cracks were composed of flat and uneven fracture surfaces at a nm scale. The flat fracture surfaces and uneven ones were nearly parallel to the cleavage plane, {11̄02}, and the basal plane, {0001}, respectively..
106. Ram Kishore, Renu Sharma, Satoshi Hata, Noriyuki Kuwano, Yoshitsuga Tomokiyo, Hameed Naseem, W. D. Brown, In-situ transmission electron microscopy investigation of aluminum induced crystallization of amorphous silicon, 2008 MRS Spring Meeting Amorphous and Polycrystalline Thin-Film Silicon Science and Technology - 2008, 1066, 345-351, 2008, The interaction of amorphous silicon (a-Si) and aluminum (Al) has been examined using in-situ transmission electron microscopy. Carbon coated nickel grids were used for depositing thin (∼50nm) amorphous silicon films using ultra high vacuum cluster tool and a thin film of Aluminum (∼50nm) was deposited subsequently on a-Si film by sputtering. The grid containing a-Si and Al films was mounted on a heating holder of FEI 200kV TEM and loaded in the TEM for viewing the microstructural and phase transformations during the in-situ heating process. The microstructural features and electron diffraction patterns in the plain view mode were observed with increase in temperature starting from 30 °C to 275 °C. The temperatures used in this experiment were 30,100,150,200, 225, 275°C . A sequential change in microstructural features and electron diffraction pattern due to interfacial diffusion of boundary between Al and amorphous Si was investigated. Evolution of polycrystalline silicon with randomly oriented grains as a result of a-Si and Al interaction was revealed. After the in-situ heating experiment the specimen was taken out and etched to remove excess of Al and the subjected to high resolution imaging under TEM and EDS analysis. The EDS analysis of the crystallized specimen was performed to locate the Al distribution in the crystallized silicon. It has been shown that Al induced crystallization can be used to convert sputtered a-Si into polycrystalline silicon as well as nanocrystalline silicon at a temperature near 275 °C by controlling the in-situ annealing parameters. The mechanism of AIC has been discussed from the experimental results and the phase diagram of Al-Si system..
107. Haigui Yang, Dong Wang, Hiroshi Nakashima, Hongye Gao, Kana Hirayama, Ken Ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Influence of top surface passivation on bottom-channel hole mobility of ultrathin SiGe- and Ge-on-insulator, Applied Physics Letters, 10.1063/1.2972114, 93, 7, 2008, Bottom-channel hole mobility was examined by a pseudo-metal-oxide- semiconductor field-effect transistors method for ultrathin SiGe-on-insulator (SGOI) and Ge-on-insulator (GOI), which were fabricated using Ge condensation by dry oxidation. By comparing samples with and without a top SiO2 layer, we investigated the influence of top surface passivation on bottom-channel hole mobility. Mobility degradation was found in an ultrathin SGOI/GOI layer without top SiO2 and became more serious with a decrease in the thickness of the SGOI/GOI layer, which strongly suggested that top surface passivation is necessary to evaluate accurate channel mobility. A 13-nm-thick GOI with passivation showed a high mobility value of 440 cm2 /V s..
108. T. Doi, H. Kitaguchi, Satoshi Hata, K. Fukuyama, K. Masuda, K. Takahashi, T. Yoshidome, Y. Hakuraku, N. Kuwano, Monotonic decrease of Tcs with thinning of the superconducting MgB2 layer in MgB2/Ni and MgB2/B alternately-layered thin films, Superconductor Science and Technology, 10.1088/0953-2048/20/12/023, 20, 12, 1223-1227, 2007.12, We prepared MgB2/Ni and MgB2/B alternately-layered films using electron beam evaporation and coaxial vacuum arc evaporation techniques without any post-annealing. The thickness of each MgB2 layer was designed to be 42, 24 or 15nm for both MgB2/Ni and MgB 2/B alternately-layered films. We confirmed that the layered structure was successfully obtained from the scanning transmission electron microscopic cross-sectional image of the MgB2/Ni alternately-layered film. The critical temperature, Tc, of the alternately-layered film decreased as the MgB2 layer became thinner, for both MgB 2/Ni and MgB2/B films. Moreover, the Tc was affected by only the MgB2 layer thickness, and was independent of the inserted layer materials..
109. 3D Observation of Dislocations in Si Single Crystal using a High-angle Triple-axis (HATA) Specimen Holder.
110. N. Kuwano, M. Hijikuro, Satoshi Hata, M. Takeuchi, Y. Aoyagi, TEM analysis of an interface layer formed by the anti-surfactant treatment on a GaN template, Journal of Crystal Growth, 10.1016/j.jcrysgro.2006.10.188, 298, SPEC. ISS, 284-287, 2007.01, Transmission electron microscope (TEM) analysis was performed for the anti-surfactant (AS)-treated interface of GaN thin films deposited by the metal-organic vapor-phase epitaxy method. It was revealed that the AS-treatment with supplying a gas-source of tetraethyl-silicon (TESi) forms an interface layer of about 1 nm thickness. The electron diffraction pattern for the interface layer shows a streak along [0 0 0 1] at about one-thrid positions between hkil=0 0 0 0 and over(1, -) 2 over(1, -) 0. The point analysis of energy dispersive X-ray spectroscopy (EDS) confirmed that the interface layer contains a certain amount of silicon. These results revealed that the interface layer is a crystalline phase of silicon compound. The effect of the interface layer on the morphology of threading dislocations was also discussed in terms of coherency of the interface layer with GaN..
111. Satoshi Hata, T. Yoshidome, H. Sosiati, Y. Tomokiyo, N. Kuwano, A. Matsumoto, H. Kitaguchi, H. Kumakura, Microstructures of MgB2/Fe tapes fabricated by an in situ powder-in-tube method using MgH2 as a precursor powder, Superconductor Science and Technology, 10.1088/0953-2048/19/2/002, 19, 2, 161-168, 2006.02, Microstructures of MgB2/Fe tapes fabricated by an in situ powder-in-tube method using MgH2 as a precursor powder have been studied by means of x-ray diffraction and analytical transmission electron microscopy combined with a focused ion beam microsampling technique. The overall microstructures in the tapes are characterized as densely crystallized MgB2 areas with 10-200 nm grain size, uncrystallized areas mainly containing MgO and amorphous phases enriched with B, and a number of holes and cracks. The crystallized MgB2 areas increase upon doping with SiC nanoparticles. Si and C atoms decomposed from SiC nanoparticles during heat treatment exhibit different spatial distributions: the Si atoms are inhomogeneously distributed, forming silicides such as Mg2Si with grain size of 5-20 nm, while the C atoms tend to be uniformly distributed in the MgB2 matrix. A significant difference in distribution of O atoms between the SiC-doped and non-doped specimens was observed. The processes of formation of these microstructures and their relationships with the critical current density under magnetic fields have been discussed..
112. Satoshi Hata, Harini Sosiati, Noriyuki Kuwano, Masaru Itakura, Takayoshi Nakano, Yukichi Umakoshi, Removing focused ion-beam damages on transmission electron microscopy specimens by using a plasma cleaner, Microscopy (Oxford, England), 10.1093/jmicro/dfl001, 55, 1, 23-26, 2006.01, A plasma cleaner is usually used for removing carbonaceous debris from a specimen and preventing contamination during transmission electron microscopy (TEM) imaging and analysis. However, the plasma cleaner can be effectively used for thinning down damage layers on TEM specimens prepared by focused ion-beam (FIB) milling. By optimizing plasma treatment conditions, the quality of high-resolution images and diffraction patterns of the FIB-milled specimens has been remarkably improved using the plasma cleaner..
113. H. Sosiati, Satoshi Hata, N. Kuwano, Y. Iwane, Y. Morizono, Y. Ohno, Microstructural characterization of whiskers and oxidized surfaceson Sn/FeNi42 and Pb-free alloys, 20th Annual Passive Components Symposium, CARTS-Europe 2006 CARTS Europe 2006, 237-243, 2006, Microstructural characterization was performed by analytical transmission electron microscopy (ATEM) to clarify the formation mechanism of tin whiskers. A tin (Sn)-layer about 10 μm thickness was electrodeposited on a FeNi42 plate. The Sn/FeNi42 plate was heated and cooled repeatedly in a temperature range of 233-403 K for 100 cycles under various atmospheres. Cross-sectional TEM specimens of whiskers on the Sn/FeNi42 plate were prepared using a focused ion beam (FIB) micro-sampling technique. Some artifact-effects of the FIB treatments on microstructures in tin alloys were taken into account. Bent-type whiskers grown on the Sn/FeNi42 are of polycrystalline β-Sn. A tin-oxide layer around 10 nm in thickness is formed on the tin surface. Electron diffraction, high-resolution TEM and electron energy loss spectroscopy (EELS) analyses revealed that the tin-oxide layer is predominantly of crystalline SnO 2. The presence of crystalline SnO was also recognized. It was found that the tin-oxide layer tends to be rather thin around stems of the whiskers. It is interpreted that thermal stress in the tin-layer breaks the thin tin-oxide layer at grain boundaries of tin and the whiskers grow from the broken area. The formation mechanism of the whiskers is discussed..
114. H. Sosiati, N. Kuwano, Satoshi Hata, Y. Iwane, Y. Morizono, Y. Ohno, Tin whisker formation on a lead-free solder alloy studied by transmission electron microscopy, 2006 8th Electronics Packaging Technology Conference, EPTC 2006 8th Electronics Packaging Technology Conference, EPTC, 10.1109/EPTC.2006.342749, 398-403, 2006, Tin whiskers grown on a Sn/Cu-plated Polyimide (PI)-flexible substrate are a serious problem in electronic industrial application, because the whiskers lead to catastrophic electrical short circuit failures. Here, we report characterization of microstructures in the whiskers grown on a surface of Sn/Cu-plated PI-flexible substrate by cross-sectional transmission electron microscopy (TEM) to analyze the behavior and the formation mechanism of whiskers. The whisker was found to be monocrystalline β-Sn and grown with the preferred directions of [110] and [101]. The whiskers formed on this tin surface are nucleated and grown by the compressive stress, that is induced externally by insertion of Sn/Cu-plated PI-flexible substrate into the connector..
115. H. Sosiati, Satoshi Hata, N. Kuwano, Y. Tomokiyo, H. Kitaguchi, T. Doi, H. Yamamoto, A. Matsumoto, K. Saitoh, H. Kumakura, Relationship between microstructure and Jc property in MgB 2/α-Al2O3 film fabricated by in situ electron beam evaporation, Superconductor Science and Technology, 10.1088/0953-2048/18/10/005, 18, 10, 1275-1279, 2005.10, A transmission electron microscopy (TEM) study has been carried out on an MgB2/α-Al2O3 film that exhibits the typical property of critical current density (Jc) under magnetic fields. The MgB2 layer of 300 nm in thickness was grown on a (001)α-Al2O3 substrate using an in situ electron beam evaporation method. Jc of the film takes significantly high values when the applied magnetic field is perpendicular to the film surface. The MgB2 layer consists of fine columnar MgB2 crystals 20-30 nm in size. The columnar MgB2 crystals grow almost perpendicular to the substrate surface and have no crystallographic orientation relationship with the α-Al2O3 substrate because of an amorphous layer formed first on the substrate. A high density of columnar grain boundaries within the MgB2 layer may be effective for the enhancement of the flux-pinning under the perpendicular magnetic field..
116. Bui Thi Hang, Tomonori Watanabe, Minato Eashira, Shigeto Okada, Jun Ichi Yamaki, Satoshi Hata, Seong-Ho Yoon, Isao Mochida, The electrochemical properties of Fe2O3-loaded carbon electrodes for iron-air battery anodes, Journal of Power Sources, 10.1016/j.jpowsour.2005.02.028, 150, 1-2, 261-271, 2005.10, The redox efficiency of iron has been improved by increasing the distribution of iron on the carbon surface with Fe2O 3-loaded carbon materials. The Fe2O3-loaded carbon material was prepared by loading Fe2O3 on carbon by a chemical method. Fe(NO3)3 was impregnated on carbon with different weight ratios of iron-to-carbon in an aqueous solution, and the mixture was dried and then calcined for 1 h at 400 °C in flowing Ar. The effect of various carbons on the physical and electrochemical properties of Fe2O3-loaded carbon electrodes was investigated with the use of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with X-ray energy-dispersive spectroscopy (EDS), cyclic voltammetry (CV) and galvanostatic cycling performance. Transmission electron microscopy coupled with X-ray diffraction measurements revealed that small Fe2O3 particles were distributed on the carbon surface. Natural graphite and several nano-carbon materials such as acetylene black and tubular carbon nanofibers (tubular CNF) exhibited improved characteristics, such as enhanced capacity and higher redox currents for the Fe2O3-loaded carbon electrode. SEM and EDS results suggest that Fe2O3-loaded nano-carbon electrodes, due to the large surface area of the nano-carbon, have more Fe2O3 dispersed than on Fe2O3-coated graphite electrodes..
117. Kousuke Kimura, Satoshi Hata, Syo Matsumura, Takao Horiuchi, Dark-field transmission electron microscopy for a tilt series of ordering alloys
Toward electron tomography, Microscopy (Oxford, England), 10.1093/jmicro/dfi060, 54, 4, 373-377, 2005.08, Here we show a technique to obtain a tilt series of dark-field (DF) transmission electron microscopy (TEM) images in ordering alloys for tomographic three-dimensional (3D) observations. A tilt series of DF TEM images of D1(a)-ordered Ni4Mo precipitates in a Ni-Mo alloy was successfully obtained by adjusting a diffraction condition for a superlattice reflection from the Ni4Mo precipitates. Since the superlattice reflection usually has a long extinction distance, dynamic diffraction effects such as thickness fringes can be suppressed to some extent with precise realignment of the diffraction condition. By using the tilt series of the DF TEM images, we attempted a computed TEM tomography to visualize 3D shapes and positions of the precipitates..
118. Satoshi Hata, Harini Sosiati, Noriyuki Kuwano, Yoshitsugu Tomokiyo, Akiyoshi Matsumoto, Masao Fukutomi, Hitoshi Kitaguchi, Kazunori Komori, Hiroaki Kumakura, Effects of heat treatments on microstructure formation in MgB 2/YSZ/hastelloy film, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2005.848834, 15, 2 PART III, 3238-3241, 2005.06, Annealing processes in MgB2 films deposited on yttria-stabilized zirconia (YSZ)-buffered Hastelloy substrates were studied by transmission electron microscopy. The MgB2 films with Mg-rich compositions were fabricated at room temperature using a pulsed laser deposition (PLD) method. The as-deposited films do not exhibit clear superconducting transitions, and have inhomogeneous microstructures composed of amorphous regions and a small amount of crystalline MgB2 and MgO with several tens of nm in size. Various sizes of voids are also incorporated within the amorphous regions. After the annealing at 600 or 680°C, the films exhibit clear superconducting transitions. The amorphous regions crystallize into fine grains of MgB 2 or MgO 5-50 nm in size. The voids remain in the annealed films and their sizes depend on the annealing condition. Magnesium-and oxygen-rich layers are formed near the MgB2/YSZ interface and the film surface. It is suggested that the finer grains of MgB2 and MgO obtained by the lower-temperature annealing give a larger critical current density under a high magnetic field..
119. Hitoshi Kitaguchi, Toshiya Doi, Yuki Kobayashi, Akiyoshi Matsumoto, Harini Sosiati, Satoshi Hata, Masao Fukutomi, Hiroaki Kumakura, Properties of MgB2 films with very high transport critical current densities, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2005.848866, 15, 2 PART III, 3313-3316, 2005.06, Magnesium diboride, MgB2, thin films are fabricated through two different kinds of process. One is an in-situ process by using electron beam deposition and the other is an ex-situ process by using the combination of pulsed laser deposition and heat treatment. The critical current density, J c, is investigated as a function of external magnetic field in the range of 0-7 T and/or temperatures ranging from 4.2 K to the critical temperature by using dc 4-probe transport method. The in-situ processed film shows very high Jc, e.g., 7.1×106, 1.2×10 6, and 1.4×105 A/cm2 in 0, 4, and 7 T (perpendicular fields), respectively. Angular dependence of Jc is much different between the two kinds of films. Jc-angle (magnetic field) curves of the in-situ processed film show two peaks; one is around the field perpendicular to the film surface and the other is around the parallel field. On the contrary, the curves of the ex-situ processed film have only one peak around the parallel field. Microstructure analyses show that the in-situ film has columnar grains aligned perpendicular to the film surface and that the ex-situ one has granular grains with random orientations. These results indicate that the grain boundaries between columnar grains act as effective pinning centers and enhance Jc in the perpendicular fields..
120. Shigeru Fujino, H. Tokunaga, Satoshi Hata, E. Saiz, A. P. Tomsia, Graded glass coatings for Co-Cr implant alloys, Journal of Materials Science, 10.1007/s10853-005-1982-z, 40, 9-10, 2499-2503, 2005.05, A graded glass coating for Vitallium®, a Co-Cr alloy, has been prepared using a simple enameling technique. The composition of the glasses has been tailored to match the thermal expansion of the alloys. The optimum glass composition and firing conditions (temperature and time) needed to fabricate homogeneous coatings with good adhesion to the alloy were determined. The final coating thickness ranged between 25 and 60 μm. Coatings fired under optimum conditions do not delaminate during indentation tests of adhesion. Excellent adhesion to the alloy has been achieved through the formation of 100 nm thick interfacial chromium-oxide (CrOx) layers. The graded glass (consisting of BIG and 6P50 layers) can be successfully coated to a Co-Cr alloy, and forms hydroxyapatite (HA) on the coating surface when immersed in a simulated body fluid (SBF) for 30 days..
121. Satoshi Hata, K. Shiraishi, Masaru Itakura, N. Kuwano, T. Nakano, Y. Umakoshi, Long-period ordering in a TiAl single crystal with a gradient composition, Philosophical Magazine Letters, 10.1080/09500830500157462, 85, 4, 175-185, 2005.04, A series of long-period superstructures (LPSs) formed in an Al-rich TiAl single crystal with a gradient composition has been observed by transmission electron microscopy. A Ti-54.7?at.%?Al single crystal was heat treated within molten Al at 1234°C, and a composition-gradient layer with an Al concentration from 55 to 75?at.% was formed at the surface of the single crystal. The composition-gradient layer exhibits ordering into different LPSs depending on the Al concentration as follows: short-range order, h-Al2Ti and one-dimensional antiphase domain structure. These LPSs have an alternate stacking of Al(002) and Ti-Al(002) layers and the ordering of the LPSs proceeds in the TiAl matrix, maintaining an orientation relationship in which Al(002) layers of the LPSs and the TiAl matrix are parallel to each other. The ordering of this type of LPS and the phase transition between these LPSs are thus interpreted as structural changes in Ti(002) layers of the Al-rich TiAl crystal. It was also observed that ordering of the orthorhombic h-Al2Ti exhibits anisotropic features depending on the direction of the composition gradient. This suggests that the long-period ordering in the TiAl crystal depends on diffusion processes as well as the local concentrations of Ti and Al atoms..
122. M. Ishimaru, Y. Hirotsu, Satoshi Hata, C. Ma, N. Nishiyama, K. Amiya, A. Inoue, Structural characterization of Cu-Ti-based bulk metallic glass by advanced electron microscopy, Philosophical Magazine Letters, 10.1080/09500830500153776, 85, 3, 125-133, 2005.03, The atomistic structure of a high-strength Cu42.5Ti41.5Ni7.5Zr2.5Hf5Si1 bulk metallic glass prepared by copper-mould casting has been characterized by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). High-resolution TEM and high-angle annular dark-field observations revealed that crystalline nanoparticles with sizes less than 10?nm are embedded in an amorphous matrix. It was confirmed by energy-dispersive X-ray spectroscopy in combination with STEM that these nanoparticles possess higher copper content than the amorphous matrix. Nanobeam electron diffraction experiments indicated that their crystalline structure is basically face-centred cubic with ordered atomic arrangements..
123. Satoshi Hata, K. Kimura, T. Horiuchi, Syo Matsumura, Y. Tomokiyo, Electron tomography of crystalline microstructures by diffraction contrast imaging
Application to ordered alloys, Microscopy and Microanalysis, 10.1017/S1431927605050026, 11, SUPPL. 2, 18-19, 2005.
124. Takayoshi Nakano, Yosuke Nagasawa, Yukichi Umakoshi, Satoshi Hata, Noriyuki Kuwano, Masaru Itakura, Yoshitsugu Tomokiyo, Ordering process and formation of anti-phase boundary in long-period superstructures of Al-rich TiAl single crystals, 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, 1, 231-236, 2005, Ordering process and subsequent formation of anti-phase boundaries (APBs) in the long-period superstructures of X3Ti2 (Ga 3Ti2), X5Ti3 (Al5Ti 3) and h-X2Ti (h-Al2Ti) in -rich TiX (X=Al or Ga) single crystals were examined by a high-resolution transmission electron microscopy. Formation of the APBs is closely related to the unique units of ordered base clusters such as Ti4X, Ti3X and Ti 2X which form square, fat rhombus and lean rhombus shapes, respectively, in the (002) Ti-rich layers of the L10 matrix. The Al5Ti3-type anti-phase domains (APDs) with various sizes in diameter are introduced in Ti-62.5at.%Al crystals by appropriate heat treatment. Almost all the X5Ti3-type APBs lie on {110) and a type of APB (named Type A) with the extremely low APB energy was found. In contrast, no APBs are introduced in X3Ti2 and h-X 2Ti because of their relatively higher energies compared with those in X5Ti3. As a result, the L10 matrix phase remains between APDs as a thin boundary phase for h-Al2Ti..
125. Satoshi Hata, K. Shiraishi, N. Kuwano, Masaru Itakura, Y. Tomokiyo, T. Nakano, Y. Umakoshi, TEM analysis of long-period superstructures in TiAl single crystal with composition gradient, Quaternary International, 842, 259-264, 2005, The ordering mechanism of long-period superstructures (LPSs) in Al-rich Ti-Al alloys was studied using a TiAl single crystal with a composition gradient. A TiAl single crystal with gradient compositions from 55 to 75 at.% Al was prepared by annealing in a molten Al at 1234°C. The single crystal exhibits long-period ordering into different LPSs depending on the Al concentration as follows: an Al5Ti3 type short-range order, h-Al2Ti and one-dimensional antiphase domain structures. These LPSs show an orientation relationship in which Al (002) layers of the LPSs are parallel to those of the TiAl matrix. The atomic arrangements of the LPSs are characterized in common as the alternate stacking of the Al (002) layers and Ti-Al (002) layers. It is thus concluded that the ordering of this type of LPSs and the phase transition between these LPSs are explained as structural changes in Ti-Al (002) layers of the Al-rich L10-TiAl crystal..
126. Satoshi Hata, K. Kimura, Syo Matsumura, Y. Tomokiyo, T. Moritani, M. Doi, Three-dimensional observation of ordered and disordered precipitates using dark-field TEM tomography, 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, 449-454, 2005, For three-dimensional (3D) observation of microstructures in ordering alloys, such as orientation variants and anti-phase domain boundaries, electron tomography using dark-field transmission electron microscopy (DF TEM) may be a potential approach. However, DF TEM tomography has been thought to be impossible because of dynamical diffraction effects in crystals. In this study, we attempted DF TEM tomography of ordered and disordered precipitates in Ni-Mo and Ni-Al-Ti alloys. A tilt series of DF images of the precipitates were obtained by precisely setting diffraction conditions for a superlattice reflection. Owing to a long extinction distance of the superlattice reflection, dynamical diffraction effects, such as thickness fringes, have been effectively suppressed. Preliminary 3D reconstruction from the obtained tilt series clearly shows qualitative morphology and relative positions of the precipitates, which suggests the feasibility of the DF TEM tomography for ordering alloys..
127. Satoshi Hata, Kohjiro Shiraishi, Masaru Itakura, Noriyuki Kuwano, Takayoshi Nakano, Yukichi Umakoshi, Application of FIB microsampling technique to long-period ordered TiAl single crystal with composition gradient, Microscopy (Oxford, England), 10.1093/jmicro/dfh049, 53, 5, 537-540, 2004.12, Metastable long-period superstructures in an LI0-TiAl single crystal with a composition gradient were observed successfully by transmission electron microscopy with a focused ion beam (FIB) microsampling technique. The composition gradient from 54.7 to 75 at.% Al with ∼6 μm width was detected by electron probe microanalysis and foil specimens containing the composition-gradient area were fabricated by the FIB microsampling method. The foil specimens clearly exhibit sequential changes in long-period superstructure depending on the Al concentration..
128. Harini Sosiati, Satoshi Hata, N. Kuwano, Y. Tomokiyo, A. Matsumoto, M. Fukutomi, H. Kitaguchi, K. Komori, H. Kumakura, Electron microscopy of MgB2 thin film on YSZ-buffered Hastelloy, Physica C: Superconductivity and its Applications, 10.1016/j.physc.2004.01.168, 412-414, SPEC. ISS., 1376-1382, 2004.10, In order to understand the relationship between the microstructures and superconducting properties of MgB2 films, analytical TEM observations have been carried out. The films were fabricated by a KrF excimer laser deposition on Hastelloy substrates precoated with YSZ (yttria-stabilized zirconia). The deposited films were annealed under Ar atmosphere at 873 K for 1 h and at 953 K for 0.5 h. The critical current densities of these films were measured to be Jc=1×105 A/cm2 and J c=7.7×103 A/cm2 at 4.2 K and 10 T, respectively. The conventional TEM observation showed nanocrystalline MgB 2 and MgO of 5-30 nm in size dispersed in the films. Voids with various sizes from 10 to 60 nm were also observed in the films. Two-dimensional elemental analyses exhibited that near the MgB2/YSZ interface the films have a layered structure where the layers enriched with Mg and O have low B concentrations complementarily. The average sizes of the MgB2 and MgO grains and the voids increase with the annealing temperature. The enhancement of Jc value of the film annealed at 873 K may be due to smaller sizes of the MgB2 and MgO grains and voids than those at 953 K..
129. H. Kitaguchi, A. Matsumoto, H. Kumakura, T. Doi, H. Yamamoto, K. Saitoh, H. Sosiati, Satoshi Hata, MgB2 films with very high critical current densities due to strong grain boundary pinning, Applied Physics Letters, 10.1063/1.1805195, 85, 14, 2842-2844, 2004.10, The production of critical current density (Jc) by 20-30 nm diameter columnar grains of MgB2 was analyzed. It was observed that 20-30 nm diameter columnar grain structure produced Jc exceeding 5×106 A/cm2. It was also observed that strongest pinning ocurred when the field was aligned parallel to the grain boundaries. The results show that grain boundaries in MgB2 do not obstruct current flow as in the high-temperature cuprate superconductors, but act like those in intermetallic superconductors such as Nb3Sn..
130. Satoshi Hata, Harini Sosiati, Yoshitsugu Tomokiyo, Noriyuki Kuwano, Akiyoshi Matsumoto, Masao Fukutomi, Hitoshi Kitaguchi, Kazunori Komori, Hiroaki Kumakura, Microstructure of MgB 2 films deposited on YSZ/Hastelloy substrate, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 68, 9, 648-655, 2004.09, Microstructures of MgB 2 films on yttria-stabilized-zirconia (YSZ) /Hastelloy substrates were studied by analytical transmission electron microscopy. The MgB 2 films with Mg-rich compositions were fabricated by pulsed laser deposition followed by annealing at 600°C or 680°C under Ar atmosphere. Fine grains of MgB 2 and MgO crystals 5-30 nm in size that shows a good mutual connectivity are formed in the MgB 2 films. The MgB 2 films also form voids 5-100 nm in size that may contain amorphous or oxide phases. Two-dimensional elemental analyses revealed that Mg and O atoms are enriched near the MgB 2/YSZ interface. From a comparison in microstructures between the 600°C- and 680°C-annealed MgB 2 films, it is suggested that the films composed of finer grains of MgB 2 exhibit a higher critical current density under high magnetic fields..
131. Satoshi Hata, Kiyoshi Higuchi, Toshitsugu Mitate, Masaru Itakura, Yoshitsugu Tomokiyo, Noriyuki Kuwano, Takayoshi Nakano, Yosuke Nagasawa, Yukichi Umakoshi, HRTEM image contrast and atomistic microstructures of long-period ordered Al-rich TiAl alloys, Microscopy (Oxford, England), 10.1093/jmicro/53.1.1, 53, 1, 1-9, 2004.03, Long-period superstructures formed in off-stoichiometric L1 0-TiAl alloys were investigated by high-resolution transmission electron microscopy (HRTEM). The HRTEM analysis combined with multislice simulation and image processing was carried out to clarify atomistic microstructures of Al5Ti3 and h-Al2Ti ordered states and a short-range ordered (SRO) state in Ti-62.5 at.% Al alloys. Aluminium atoms in the (002) Ti layers form square-, lean rhombus- and fat rhombus-type ordered clusters in the SRO state. The ordered clusters are in contact with each other and form microdomains of various long-period superstructures. The ordered clusters are tiled periodically in a long range to form Al5Ti3 or h-Al2Ti domains and characteristic antiphase boundary structures..
132. Satoshi Hata, K. Higuchi, T. Mitate, N. Kuwano, Masaru Itakura, Y. Tomokiyo, T. Nakano, Y. Nagasawa, Y. Umakoshi, HRTEM Observation of Partially Ordered Long-Period Superstructures in Al-Rich TiAl Alloys, Quaternary International, 753, 175-180, 2003, Atomistic microstructures of long-period superstructures in Al-rich TiAl alloys were investigated by high-resolution transmission electron microscopy, The multi-slice image simulation revealed that Al-atoms in Ti-rich (002) layers of the superstructures are imaged as very bright dots under appropriate observing conditions. By enhancing the contrast of the very bright dots using an image processing technique, partially ordered long-period superstructures were clearly characterized. For the short-range order state, A4B, A2B and A3B type ordered-clusters are generated in the Ti-rich (002) layers. These ordered-clusters are in contact with each other, and form local microdomains of various superstructures, such as Al 5Ti3, h-Al2Ti and so on. For the Al 5Ti3 and h-Al5Ti ordered states, the ordered-clusters are tiled periodically to form the Al5Ti 3 or h-Al2Ti domains and characteristic anti-phase boundary structures..
133. T. Nakano, Y. Nagasawa, Y. Umakoshi, Satoshi Hata, N. Kuwano, Masaru Itakura, Y. Tomokiyo, Selectivity of anti-phase boundary introduced in Al5Ti3 superstructure, Materials Science Forum, 426-432, 2, 1763-1770, 2003, Formation of anti-phase boundaries (APBs) in the Al5Ti3 long-period superstructure of Al-rich TiAl single crystals was examined by the high-resolution transmission electron microscopy (HRTEM) with image processing. The APBs were analyzed focusing on the unique units of ordered clusters such as Ti4Al, Ti3Al and Ti2Al which form square, fat rhombus and lean rhombus shapes in (002) Ti-rich layers, respectively. The Al5Ti3-type anti-phase domains (APDs) with various sizes in diameter were obtained in Ti-62.5at.%Al crystals by heat treatment at 600°C or 750°C after the floating zone melting and the subsequent quenching from 1200°C. Almost all the Al5Ti3-type APBs lay on {110) and were geometrically classified into 19 types named Type A to Type S. Indeed, 6 types of APBs (Type A to Type F) composed of the units of Ti4Al, Ti3Al and Ti2Al were found, but the other 13 types (Type G to Type S) were not clearly observed. Moreover, a specific type called Type A among the APBs was preferentially formed even in the initial stage of the APD growth. The APBs of Type A appeared with a quite higher frequency than those ideally formed by the random-nucleation and subsequent bounding of APDs. Thus, the APBs of Type A must be already introduced in the stage for nucleation of the APDs and grow stably on {110) due to the quite low APB energy in the long-period superstructure with a relatively large unit cell..
134. Satoshi Hata, T. Nakano, K. Higuchi, Y. Nagasawa, N. Kuwano, Masaru Itakura, Y. Tomokiyo, Y. Umakoshi, Semi-quantitative HRTEM for partially ordered materials
Application to Al-rich TiAl alloys, Materials Science Forum, 426-432, 2, 1721-1726, 2003, Microstructures of long-period ordered TiAl alloys that are rich in Al were investigated by the semi-quantitative high-resolution transmission electron microscopy (HRTEM). Local ordered arrangements of Al atoms in (002) Ti-rich layers of the L 10 matrix were identified from arrangements of very bright dots in the HRTEM images after appropriate image processing. For a short-range order (SRO) state, the Al atoms form three types of ordered-clusters: square (Ti4Al), fat rhombus (Ti3Al) and lean rhombus (Ti2Al). These clusters are arranged periodically in a short-range to form microdomains of various long-period superstructures: Al5Ti3, h-Al2Ti and so on. Below or above the temperature range showing the SRO state, the Al5Ti3 or h-Al2Ti type cluster-arrangements selectively develop into their long-range order (LRO) domains. Some of the other cluster-arrangements are left between the LRO domains as anti-phase boundary structures..
135. Satoshi Hata, K. Higuchi, Masaru Itakura, N. Kuwano, T. Nakano, K. Hayashi, Y. Umakoshi, Short-range order in Al-rich γ-TiAl alloys studied by high-resolution transmission electron microscopy with image processing, Philosophical Magazine Letters, 10.1080/09500830210137425, 82, 7, 363-372, 2002.07, The atomic arrangements of short-range order (SRO) in two Al-rich γ-TiAl alloys with 62.5 and 60.0 at.% Al respectively have been investigated by high-resolution transmission electron microscopy with image processing. For both alloys, SRO structures are formed in Ti-rich (002) layers of the Ll0 ordered γTiAl matrix, in the course of the phase transformation from the Al5Ti3 long-period superstructure phase at lower temperatures to the h-Al2Ti phase at higher temperatures. The SRO structures are composed of three types of ordered cluster: Ti4Al type (square shaped), Ti3Al type (fat rhombus shaped) and Ti2Al type (lean rhombus shaped). The ordered clusters form local microdomains of the Al5Ti3 and Al3Ti2 superstructures in addition to the Al5Ti3 and h-Al2Ti superstructures, by different methods of tiling the ordered clusters. Such ordered clusters or microdomains tend to be in contact with each other through common (310) boundaries. This results in peculiar diffuse streaks in diffraction connecting intensity maxima arising from the long-period superstructures..
136. Satoshi Hata, T. Mitate, N. Kuwano, Syo Matsumura, D. Shindo, K. Oki, Short range order sturctures in fcc-based Ni-Mo studied by high resolution transmission electron microscopy with image processing, Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 10.1016/S0921-5093(00)01872-4, 312, 1-2, 160-167, 2001.08, Modern high resolution transmission electron microscopy was employed in study of short range order (SRO) in fec-based Ni-Mo, which is classified as '1 1/2 0 alloy'. Digital processing of high resolution transmission electron microscope (HRTEM) images can give information about local atomic arrangements of SRO as well as their projection views. The HRTEM observation with image processing reveals the SRO structures in Ni-Mo depending upon the alloy composition and the heat treatment. Subunit cell clusters of D1a, DO22 and Pt2Mo structures are generated in the SRO states of Ni4Mo and Ni3Mo alloys. In the initial SRO stales, the number of Pt2Mo type clusters increases with Mo composition while that of D1a type decreases. The D1a, DO22 and Pt2Mo type clusters increase in number in the early stages of subsequent ordering. The formation of D1a DO22 and Pt2Mo type clusters in the SRO states is rationalized in terms of the similar tendencies in atomic configuration between D1a DO22 and Pt2Mo structures..
137. N. Tanaka, Satoshi Hata, K. Oki, N. Kuwano, HAADF-STEM observation of partially ordered Ni4Mo alloys, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.65.5_414, 65, 5, 414-418, 2001.01, Partially ordered Ni4Mo alloys were observed for the first time at an atomic resolution with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The Mo atomic columns in the D1a ordered structure were clearly visualized as bright square dots in the HAADF-STEM image. It was found that the ordered regions were observed with a high contrast in the defocus condition a little overfocused from the Scherzer defocus (Δf = √CS · γ) which is the condition for the smallest electron probe in STEM. The phenomenon was interpreted successfully by using the approximate imaging theory for HAADF-STEM proposed by Jesson et al. Using the present experimental and simulation results, an approximate imaging theory for visualizing short range ordered state in binary alloys, such as the Ni4Mo alloys, is proposed..
138. Satoshi Hata, K. Oki, T. Hashimoto, N. Kuwano, Microstructures of Ti50Al45Mo5 alloy powders produced by plasma rotating electrode process, Journal of Phase Equilibria and Diffusion, 10.1361/105497101770332938, 22, 4, 386-393, 2001.01, Microstructures of Ti50Al45Mo5 (at.%) alloy powders produced by the plasma rotating electrode process (PREP) were investigated. The powders have inhomogeneous structures, which consist of dendrites and rounded grains. The dendrites, which show a "rosettelike" morphology, are formed on the powder surface and around the rounded grains. The rosettelike dendrites are of hexagonal α2 (D019) phase even though the dendrites have an equiaxial morphology, and a small amount of β2 (B2) phase is also contained inside. It is suggested that the solidification to α (hcp-A3) phase occurred by the peritectic reaction between the primary β (bcc-A2) dendrites and the liquid: L + β → L + β + α. The rounded grains, on the other hand, are of β2 phase in which acicular α or α2 laths are precipitated with the Burgers orientation relationship. Antiphase domain boundaries in the β2 matrix are intersected by α(α2) laths. It is interpreted that the α(α2) laths were formed by the solid-state transformations: β2 → β2 + α → β2 + α2. The formation of the two different microstructures in the powder particles is rationalized in terms of the changes in local composition of the liquid phase during the rapid solidification process..
139. Satoshi Hata, D. Shindo, T. Mitate, N. Kuwano, Syo Matsumura, K. Oki, HRTEM image contrast of short range order in Ni4Mo, Micron, 10.1016/S0968-4328(99)00134-1, 31, 5, 533-538, 2000.10, The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni4Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni4Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N2M2-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N2M2 patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1(a), D022 and Pt2Mo structures. The N2M2-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast. (C) 2000 Elsevier Science Ltd..
140. N. Tanaka, N. Suzuki, M. Kawasaki, Satoshi Hata, N. Kuwano, K. Oki, High-angle annular dark-field STEM of partially ordered Ni-19.5at%Mo alloys, European Physical Journal: Special Topics, 10, 6, 2000.01, Atomic structures of partially ordered Ni-19.5at%Mo alloys are, for the first time, studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The small ordered regions with a D1a structure are clearly visualized as the square-arrangement of bright clots corresponding to the Mo-atomic columns in the dark background due to the disordered matrix with a fcc structure. The variation of the image contrast, where the D1a structure is visualized with high contrast in overfocused conditions from the Scherzer defocus, is observed, which is interpreted by using the approximate imaging theory by Jesson et al. and the size-variation of the probe. The imaging theory for the HAADF-STEM of short-range ordered state in binary alloys is formulated, where the dynamical diffraction effect is reduced in comparison with that for transmission electron microscopy (TEM)..
141. Satoshi Hata, Syo Matsumura, N. Kuwano, K. Oki, D. Shindo, Short range order in Ni4Mo and its high resolution electron microscope images, Acta Materialia, 10.1016/S1359-6454(98)00180-3, 46, 14, 4955-4961, 1998.09, The short range ordered (SRO) structure in Ni4Mo has been investigated by means of high resolution transmission electron microscopy with digital image processing and Monte Carlo simulation. High resolution transmission electron microscope (HRTEM) images were recorded with an Imaging Plate (IP) system. Conventionally printed images of the SRO state exhibit locally dot patterns corresponding to N2M2-type (chalcopyrite-like) structure. However, the dot patterns transform into those of subunit cell clusters of D1a, D022 and Pt2Mo structures, when the image is output with a different gray scale. The Monte Carlo simulation with appropriate interaction parameters of atoms has explained successfully the HRTEM images. It is concluded that the SRO state in Ni4Mo involves subunit cell clusters of D1a, D022 and Pt2Mo structures in the atomistic level of microstructure. The concept of 〈11/20〉* static concentration waves corresponding to the N2M2 pattern is rationalized as a mesoscopically averaging view of the SRO state..
142. Satoshi Hata, Syo Matsumura, Noriyuki Kuwano, Kensuke Oki, Short range order and its transformation to long range order in Ni4Mo, Acta Materialia, 10.1016/S1359-6454(97)00314-5, 46, 3, 881-892, 1998.01, The short range ordered (SRO) state and the time-evolution of the long range ordered (LRO) structure of D1a in a Ni4Mo alloy were investigated by Monte Carlo simulation based on an f.c.c. Ising model and by transmission electron microscopy (TEM). The simulation using appropriate values for pairwise atomic interactions up to the fifth nearest neighbors bears diffuse intensity maxima at {1 1/2 0} positions in the Fourier power spectrum for the early stage of SRO, and then the maxima shift to {4/5 2/5 0} for the stable Dla structure as the long range ordering proceeds. The present results are in good agreement with the temporal change in electron diffraction due to the SRO-LRO transition in a quenched Ni4Mo. The SRO state obtained in the simulation contains microclusters of subunit cells of D1a, D022 and Pt2Mo structures. If such a mixed state of microclusters is projected onto a two-dimensional {100} plane in a similar way to high resolution TEM, the mixed state exhibits locally a dot-pattern analogous to the projected N2M2-type (chalcopyrite-like) structure, which gives rise to superlattice reflections at {1 1/2 0}. This suggests that a statistically averaging view of the mixture of microclusters leads to the concept of static concentration waves of k = 1 1/2 0, which has been often employed to describe the SRO state. The formation of D022 and Pt2Mo-type subunit cells in addition to stable D1a is explained in terms of their structural relationship. The transformation from SRO to LRO is attributed to continuous growth of D1a segments into ordered domains..
143. Satoshi Hata, Daisuke Shindo, Noriyuki Kuwano, Syo Matsumura, Kensuke Oki, Interpretation of high resolution transmission electron microscope images of short range ordered Ni4Mo, Materials Transactions, 10.2320/matertrans1989.39.914, 39, 9, 914-919, 1998, High resolution transmission electron microscope (HRTEM) image contrast of short-range order (SRO) in Ni4Mo alloys has been investigated by means of multi-slice simulations. The HRTEM image contrast of SRO in Ni4Mo coincides with a projection contrast of an SRO structure which involves D1a, D022 and Pt2Mo-type subunit cells in a disordered matrix. Multi-slice simulations revealed that the SRO structure exhibit a projection contrast in the HRTEM image when the fundamental fcc lattice reflections contribute sufficiently to HRTEM imaging. The results indicate that the image of SRO in Ni4Mo can be interpreted in terms of projected potential of atomic columns under an appropriate imaging condition..
144. Satoshi Hata, H. Fujita, C. G. Schlesier, Syo Matsumura, N. Kuwano, K. Oki, Monte Carlo study of ordering processes in fcc-based Ni-Mo alloys, Materials Transactions, 10.2320/matertrans1989.39.133, 39, 1, 133-138, 1998, The Monte Carlo simulations were carried out to clarify the ordering mechanisms in fcc-based Ni-Mo alloys of Ni4Mo, Ni3Mo and Ni2Mo. When the pairwise atomic interactions up to the eighth coordinate shells are taken into account, the simulation results are consistent with the experimental changes in electron diffraction pattern during the ordering processes in Ni4Mo, Ni3Mo and Ni2Mo alloys. In the early stage of ordering, subunit cell clusters of D1a, D022 and Pt2Mo structures are first generated to form the short range ordered (SRO) state. The selective growth of stable D1a and/or Pt2Mo-type ordered domains is involved in the transition to the long range ordered (LRO) state in the following stage..
145. Syo Matsumura, T. Hino, Satoshi Hata, K. Oki, Time-evolution of 〈1/2 1/2 1/2〉* special point ordering in fcc-based binary alloys studied by Monte Carlo simulation, Materials Transactions, 37, 12, 1748-1757, 1996.12, The Monte Carlo method of simulation was employed in the study of time-evolution of atomic long-range ordering with k* = 1/2 1/2 1/2 in an fcc Ising-model system with first- and second-neighbor pairwise interactions V(1) and V(2). The results should refer to the ordering behavior of carbon atoms and vacancies in metalloid-deficient transition-metal monocarbides, such as TiC1-x and NbC1-x. Fourier power spectra of the obtained atom-configuration involve diffuse streaks in the early stage of the ordering process, and then exhibit sharp spots at k* = 1/2 1/2 1/2 and its equivalent positions in the late stage. When V(1) has a tendency to create unlike-atom pairs in a similar way to V(2), the spectra in the early stage resemble diffraction patterns of TiC1-x and NbC1-x with short-range order. Warren-Cowley parameters α's for atomic pair-correlations increase monotonically with time in even-order coordination shells, suggesting continuous evolution of the 1/2 1/2 1/2-type ordering. In contrast, the values of α for odd-order coordination shells first get enhanced with time and then decrease after reaching a peak. The behavior of odd-order α's is explained in terms of the destructive interference (or frustration) between interactions V(1) and V(2). Two different ordered structures of CuPt (R3m) and cubic (Fd3m) types, which are degenerate in the internal energy, simultaneously appear and their ordered domains grow with time..