| 1. |
Hiroshi Nakajima, Akihiro Osako, Noriharu Yodoshi, Yoshiharu Yamada, Hirofumi Tsukasaki, Ken Harada, Yuki Sakai, Kei Shigematsu, Takumi Nishikubo, Masaki Azuma, Shigeo Mori, Magnetization controlled by crystallization in soft magnetic Fe-Si-B-P-Cu alloys, MICROSCOPY, doi.org/10.1093/jmicro/dfac042, 2022.08. |
| 2. |
Y. Hirayama, M. Shigeta, Z. Liu, N. Yodoshi, A. Hosokawa, K. Takagi, Anisotropic Nd-Fe ultrafine particles with stable and metastable phases prepared by induction thermal plasma, JOURNAL OF ALLOYS AND COMPOUNDS, 10.1016/j.jallcom.2021.159724, 873, 2021.08. |
| 3. |
Evaluation of Porosity in Gas-atomized Powder by Synchrotron X-ray CT and Investigation of the Effect of Gas Species. |
| 4. |
無容器凝固法による高品位鉄系金属ガラス原料粒子の合成と1粒子の粘性流動加工プロセスによる高精度・高強度マイクロ部品の創製. |
| 5. |
Noriharu Yodoshi, Shunpei Ookawa, Rui Yamada, Naoyuki Nomura, Keiko Kikuchi, Akira Kawasaki, Effects of nanocrystallisation on saturation magnetisation of amorphous Fe76Si9B10P5, Materials Research Letters, 10.1080/21663831.2017.1398191, 6, 1, 100-105, 2018.01, © 2017 The Author(s). Amorphous Fe76Si9B10P5 particles were fabricated by a container-free solidification process and subsequent annealing, and their structural and magnetic properties were investigated by X-ray diffraction analysis, transmission electronic microscopy, and vibrating sample magnetometry. The annealing induced the nanocrystallisation of α-Fe and Fe-B compounds. The proportions of the different crystalline phases formed were dependent on the annealing temperature. The saturation magnetisation of the single particles was higher than that of the samples prepared by a conventional quenching process; this was attributable to the higher homogeneity of the nanocrystalline grains of the former as well as their higher α-Fe to Fe-B compound ratio. (Figure presented) IMPACT STATEMENT We have investigated single particles obtained by a container-free solidification process to gain deeper insight into their magnetic properties than is possible with samples obtained by conventional processes.. |
| 6. |
Jian Luan, Parmanand Sharma, Noriharu Yodoshi, Yan Zhang, Akihiro Makino, Mechanically strong nanocrystalline Fe-Si-B-P-Cu soft magnetic powder cores utilizing magnetic metallic glass as a binder, AIP Advances, 10.1063/1.4944766, 6, 5, 2016.05, © 2016 Author(s). We report on the fabrication and properties of soft magnetic powder cores with superior mechanical strength as well as low core loss (W). Development of such cores is important for applications in automobiles/devices operating in motion. High saturation magnetic flux density (Bs) Fe-Si-B-P-Cu powder was sintered with Fe55C10B5P10Ni15Mo5 metallic glass (MG) powder in its supercooled liquid state by spark plasma sintering. The sintered cores are made from the nanocrystalline powder particles of Fe-Si-B-P-Cu alloy, which are separated through a magnetic Fe55C10B5P10Ni15Mo5 MG alloy. Low W of ∼ 2.2 W/kg (at 1T and 50 Hz), and high fracture strength (yielding stress ∼500 MPa), which is an order of magnitude higher than the conventional powder cores, were obtained. Stronger metal-metal bonding and magnetic nature of MG binder (which is very different than the conventional polymer based binders) are responsible for the superior mechanical and magnetic properties. The MG binder not only helps in improving the mechanical properties but it also enhances the overall Bs of the core.. |
| 7. |
Yan Zhang, Parmanand Sharma, Noriharu Yodoshi, Akihiro Makino, Production of a magnetic material with the ability to change from very soft to semi-hard magnetic, Journal of Applied Physics, 10.1063/1.4916812, 117, 17, 2015.05, © 2015 AIP Publishing LLC. Development and magnetic properties of an alloy that can change from very soft to semi-hard magnetic are reported. We found that as quenched ribbons of Fe75.3Pt8B12P4Cu0.7 alloy are amorphous by X-ray. Heat treatment in the temperature range of 400-450°C causes formation of many α-Fe grains in the amorphous matrix. Hard magnetic L10 FePt grains appear at ∼520°C. This alloy shows a high saturation magnetic flux density [Bs (≈ Ms)>1.55T] along with the ability to vary coercivity (Hc) from ∼25A/m to 11000A/m. The Hc can be increased further to more than 21000A/m, but at the expense of a significant decrease in Bs. The ability to control magnetic properties lies in a precise control over the soft and hard magnetic phases, which are strongly exchange coupled.. |
| 8. |
Effects of Cooling Rates and Container Walls in Preparation of Spherical Fe and Pd Based Metallic Glassy Particles
Preparation of Fe-based and Pd-based metallic glassy particles with a diameter of around 500 μm were investigated. Firstly, we measured the critical cooling rate of Pd42.5Cu30Ni7.5P20 metallic glass and our results showed that its critical cooling rate was about 0.4 K/s. Pd-based metallic glassy spherical particles with fully amorphous structure were successfully prepared by heating the samples on the Al2O3 substrate up to their melting points and cooling under the cooling rate of around 3 K/s. In contrast, [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glassy particles cannot be prepared by the same process. This seemed to be caused by a reaction between the Fe-based metallic glass and the Al2O3 substrate around its melting point. This result suggested that containerless solidification method is expected to be used to prepare Fe-based metallic glassy particles. We successfully prepared mono-sized spherical particles of [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glass by Pulsated Orifice Ejection Method (POEM) as an ideal process for Fe-based metallic glasses.
. |
| 9. |
Consolidation of Fe-Based Metallic Glassy Powder by Pressure Infiltration and Squeezing Liquid Phase Sintering
In a previous paper we reported that slightly pressurized liquid phase sintering permits to fabricate fully dense Fe-based metallic glass composites, that the phase content of dual phase structure can be controlled by pressure squeezing of the liquid phase, and that the fracture strength increases with an increase in solid phase volume fraction. Throughout the process the pore shape at the contact of the particles, and accordingly the shape of the liquid phase at the particle contacts, were found to keep a cusp-shaped morphology, which implies and guarantees a complete penetration of the molten alloy into the pore space. In the present study, a model experiment was employed using a mono-sized spherical Fe-based metallic glassy powder to show an advantage of the present process for the fully dense composite structure and for the control of the composition of the two phase structure. Two types of experiments were conducted; one is pressure infiltration in which hot pressed solid skeleton was impregnated with a molten alloy, and the other is a squeezing liquid phase sintering, in which a mixture of the solid metallic glass powder and a liquid-phase alloy powder was hot pressed to control the relative density and the content of the liquid phase by squeezing out the molten alloy. The squeezing liquid phase sintering was found to give fully dense compacts, compared to the solid sintering of the metallic glass powder, which gives the relative density of 97.5% at most. An incomplete penetration of molten alloy into the dense preform and also the formation of peripheral pores near the die wall in the case of the infiltration process are discussed.
. |
| 10. |
Ayako Miura, Wei Dong, Masahiro Fukue, Noriharu Yodoshi, Kenta Takagi, Akira Kawasaki, Preparation of Fe-based monodisperse spherical particles with fully glassy phase, Journal of Alloys and Compounds, 10.1016/j.jallcom.2011.02.044, 509, 18, 5581-5586, 2011.05, In this study, we prepared monodisperse spherical particles of a desired diameter using [(Fe0.5Co0.5)0.75B 0.2Si0.05]96Nb4 alloy; the particles were prepared by using an atomization process developed by us. The particles have perfect sphericity and narrow size distribution along with a homogeneous composition. The phase transitions of particles from the fully glassy phase to the crystalline phase via mixed phase structures occurred as the particle diameter was increased; the particles produced in the fully glassy phase in an argon atmosphere had a diameter of less than 300 μm. This allowed the estimation of the intrinsic critical cooling rate for the particles with a fully glassy phase, Rc:Rc varied in the range of 700-900 K/s and depended only on the initial temperature of the alloy melt. © 2011 Elsevier B.V. All rights reserved.. |
| 11. |
Investigation on Structures of Mono-Sized Particles Prepared by Pulsated Orifice Ejection Method and the Critical Cooling Rate for Forming Glass Phase Structure
Mono-sized [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 alloy particles with desired particle size and high sphericity have been prepared by Pulsated Orifice Ejection Method (POEM). Each particle has uniform compositional distribution along with the same composition during processing. Phase transition of a particle from fully amorphous to amorphous/crystalline and then fully crystalline shows that the diameter of a single fully amorphous particle is less than 300 μm in Ar atmosphere and 700 μm in He atmosphere. The critical diameter of a fully amorphous phase particle shifts toward larger diameter with an increase in the initial melt temperature. The critical cooling rate to realize fully amorphous phase is estimated to be in the range of (700-900 K×s-1), which only depends on the initial melt temperature, irrespective of the atmospheres gases.
. |
| 12. |
Synthesis of Fe Based Metallic Glass-Pd Based Metallic Glass Composite by Slightly Pressured Liquid Phase Sintering
To consolidate [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glass powder to full density, a pressurized liquid phase sintering was employed, which was intended to promote densification by an enhanced wetting of a liquid phase with solid particles. Pd42.5Ni7.5P20Cu30 metallic glass powder, which has been reported to have a high glass forming ability and the lowest critical cooling rate of glass formation of 0.067 K/s, was chosen a liquid phase component. The melting point of the Pd42.5Ni7.5P20Cu30 metallic glass alloy of 763 K is lower than the glass transition temperature of the [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glass alloy of 808 K. However, the wettability of this alloy with the Pd42.5Ni7.5P20Cu30 alloy was revealed to be poor. Therefore, sintering pressure was applied to the compacts to promote a viscous flow deformation of solid particles and also to enhance the intergranular permeation of the liquid phase. A specially designed micro-hot press was devised for the pressure-sintering experiment. A pseudo wettability was observed during pressure-sintering, and the liquid phase was found to fill completely the intergranular space of the powder compact. The relative density of 64-95%, as well as the sintering structure, could be controlled by the punch displacement to squeeze out a part of the liquid phase from the compact. The compressive fracture strength of the obtained metallic glass composite was found to be as high as 2051 MPa, and the fracture was observed to be intragranular type, suggesting a good bonding in the particle-binding phase interface.
. |
| 13. |
Consolidation of Fe-Co Based Metallic Glassy Powder by SPS Method
Metallic glasses have been reported to exhibit excellent properties such as high strength, high corrosion resistance, high wear resistance, resulting from their random structure. In addition, metallic glasses usually exhibit a drastic reduction in viscosity in the supercooled liquid region. Therefore, metallic glasses have excellent workability in this temperature range and it has already been reported that large size of bulk metallic glasses are successfully fabricated in several Zr-, Pd-based metallic glasses.
In recent years, Fe-based metallic glasses have been intensively studied because of their excellent mechanical performance, excellent magnetic properties and rich resources. However, due to their poor glass forming ability, the size of bulk metallic glasses is limited using a copper mold casting technique.
In the present study, [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 bulk metallic glasses are fabricated by spark plasma sintering (SPS) of amorphous powders which have been prepared by a gas atomization. To find optimum conditions in the SPS process, Time-Temperature-Transformation diagram (TTT diagram) is also constructed by isothermal differential scanning calorimetry. After consolidation of metallic glassy powders, mechanical properties of consolidated glassy specimens are measured by compressive tests.
As a result, the TTT diagram can be constructed and maximum incubation time can be predicted at any holding temperature. Using SPS method, large size and nearly 100% relative dense glassy compacts are obtained with a loading pressure of 75 MPa and 400 MPa, comprising full amorphous in the case within incubation time. Compressive tests indicate that mechanical properties of consolidated specimens are still low, and one of the reasons may be the formation of approximately 50 nanometer crystalline phases between each particle observed by Transmission Electron Microscope (TEM).
. |
| 14. |
Preparation of Mono-sized Fe-based Metallic Glass Micro Particles by Pulsated Orifice Ejection Method and Evaluation of the Particles
The mono-sized [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 metallic glass micro spherical particles with narrow size distribution and high sphericity have been successfully prepared by Pulsated Orifice Ejection Method (POEM). The desired size of particles can be formed by adjusting process parameters, such as the rod displacement, the time for reaching the pulse voltage from zero voltage, the applied pressure and so on. The glassy fraction determined by enthalpy released for the particles during continuous heating in DSC, based on 70.23 J·g−1 as the enthalpy released of a fully amorphous particle (as proved by X-ray diffraction), shows that the changes of phase in one particle from single amorphous phase to amorphous crystalline mixed phase and then overall crystalline occur within the range of 350 mm and 400 mm in diameters. The critical cooling rate for the occurrence of crystalline in single amorphous phase is estimated to be within the range of 700 and 800 K·sec−1, which is slightly lower than that measured by time-temperature transformation diagram of the bulk metallic alloy, and supposed to be affected by the initial temperature of the melt.. |
| 15. |
Densification Control in Hot Pressing of Metallic Glass Powders
The equations for the densification control by viscous flow in the hot pressing of metallic glass powders are derived and a criterion for the full densification thereof and an approach for the porosity control are proposed. The kinetic equations are derived on the basis of Arzt's hot pressing theory; in which the densification is modeled by the contraction of the Bolonoi cell of the random dense packing of spherical particles. The constitutive equation for the viscous flow is obtained from the hitherto proposed creep rate equation setting the rate exponent to be unity. The hypothetical constraint for the deformation due to the three grain edges formed in the later stage of densification is taken into account as a modification of the pressure term in the kinetic equations. The relative density is expressed as functions of hot pressing time and the ratio of the viscosity and the pressure. It is shown that the time required for full densification of metallic glass powders depends only on the viscosity/pressure ratio. The criterion for the full densification is expressed as a straight line on the time-viscosity/pressure ratio plane, which divides the area into full-dense and porous areas. The porosity control of the metallic glass powder compacts is also demonstrated as another practical application of the present theory. The results are discussed on the basis of the reported data.. |
| 16. |
Synthesis of Mono-Sized Fe-Co Based Metallic Glass Particles by Pulsated Orifice Ejection Method
Metallic glasses are potentially applied for accurate micro parts because of their good formability and transferability as well as high mechanical properties and excellent magnetic properties. So the raw materials that the volume is precisely controlled are needed for a highly accurate processing. In this study, mono-sized spherical particles of Fe-Co-based metallic glass were prepared by Pulsated Orifice Ejection Method (POEM) and the capabilities of their micro-forming process in the glass transition temperature were investigated.
Mono-sized spherical particles of Fe-Co-based metallic glass particles with 200-500 μm of diameter have been obtained by Pulsated Orifice Ejection Method (POEM). The XRD pattern of the particles shows only broad peaks without any crystalline peak. A bright field TEM image of the particles and the selected area diffraction patterns shows only halo patterns that indicate fully amorphous phase. DSC curve shows that supercooled liquid region was ΔT=48 K and a TTT curve can be constructed by isothermal DSC.
. |
| 17. |
Tokujiro Yamamoto, Noriharu Yodoshi, Teruo Bitoh, Akihiro Makino, Akihisa Inoue, Soft magnetic Fe-based metallic glasses prepared by fluxing and water-quenching, REVIEWS ON ADVANCED MATERIALS SCIENCE, 18, 2, 126-130, 2008.06, [(Fe(0.5)Co(0.5))(0.75)B(0.20)Si(0.05)](96)Nb(4) soft magnetic bulk metallic glasses were prepared by fluxing and water-quenching in a silica tube. Dimension of the bulk metallic glass specimens was up to 7.7 mm in diameter, which is about 1.5 times larger than those prepared by Cu mold-casting. The critical cooling rate of [(Fe(0.5)Co(0.5))(0.75)B(0.20)Si(0.05)](96)Nb(4) alloys with fluxing for forming a metallic glass phase was 150-170 K/s, which was considerably smaller than that without fluxing. Saturation magnetization was 1.13 T, and coercivity was lower than 20 A/m. Fluxing suppresses heterogeneous nucleation by isolating the nucleation sites from the molten alloys and improves their glass-forming ability.. |
| 18. |
Tokujiro Yamamoto, Noriharu Yodoshi, Hisamichi Kimura, Akihisa Inoue, Effects of additional elements on microstructures of Zr-based metallic glass ribbons, THERMEC 2006, PTS 1-5, 10.4028/www.scientific.net/MSF.539-543.2000, 539-543, 2000-+, 2007.03, Effects of Fe, Co and Al addition to Zr55Al10Ni5Cu30 and Zr70Cu30 metallic glass ribbons were studied. 20 at.% of Fe addition prevented Zr55Al10Ni5Cu30 molten alloys from being supercooled and resulted in nanocrystallization, while Zr55Al10Ni5Cu30 alloys containing 20 at.% Co could be quenched into a supercooled liquid region. Fe addition also degraded Zr70Cu30 metallic glass, while Al addition improved both glass phase stability and mechanical properties. Degradation of Zr-based metallic glass by Fe addition originates in the large negative enthalpy of mixing Fe with Cu.. |
