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Shiotani, Kohei; Niiyama, Tomoaki*; Shimokawa, Tomotsugu*
Materials Transactions, 66(6), p.704 - 711, 2025/04
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)no abstracts in English
Fang, W.*; Liu, C.*; Zhang, J.*; Xu, P. G.; Peng, T.*; Liu, B.*; Morooka, Satoshi; Yin, F.*
Scripta Materialia, 249, p.116046_1 - 116046_6, 2024/08
Times Cited Count：4 Percentile：51.23(Nanoscience & Nanotechnology)Wakai, Eiichi; Noto, Hiroyuki*; Shibayama, Tamaki*; Furuya, Kazuyuki*; Ando, Masami*; Kamada, Takaharu*; Ishida, Taku*; Makimura, Shunsuke*
Materials Characterization, 211, p.113881_1 - 113881_10, 2024/05
Times Cited Count：12 Percentile：83.26(Materials Science, Multidisciplinary)The microstructures and mechanical properties of bcc iron-based high entropy alloy (HEA) Fe-20Mn-15Cr-10V-10Al-2.5C (in at%) without Co and Ni elements have been investigated for applications in fields such as accelerator-target system, nuclear reactors and magnetic motors in aircraft and automobiles. This alloy was normalized at 1150
C for 2 hr and then water quenched, and it was heated at 800C for 10 min and then water quenched. The alloy had a bcc-phase and vanadium carbides with 2-3 
m arranging along grain boundaries, and the Vickers hardness was 520 Hv, harder than pure tungsten. Magnetic domain structure was observed in phase differential contrast method in scanning transmission electron microscope, and the micro-size magnetic domains in grain and sub micro size ones were formed near surface, and it is attractive to the magnetic motor field application. Element distribution in nano scale (20 nm) was observed in matrix, and the presence of crystal lattice disorder in the atomic level region was seen. Very high performance for radiation resistance was confirmed with no irradiation hardening at 300 and 500 C to 1 dpa. It can be speculated that this is due to irradiation-induced nanoscale concentration changes and strain relaxation in the HEA. These properties are very attractive in application of several fields.
Wakai, Eiichi; Noto, Hiroyuki*; Shibayama, Tamaki*; Furuya, Kazuyuki*; Wakui, Takashi; Ando, Masami*; Makimura, Shunsuke*; Ishida, Taku*
Science Talks (Internet), 8, p.100278_1 - 100278_4, 2023/12
High entropy alloys tend to combine high strength with good ductility due to their inherent properties. This material is considered as a promising new material not only for higher-performance future general industrial applications, but also for increasing the durability and range of application of radiation-affected equipment in nuclear and radiation environments, and has been rapidly gaining attention in recent years. In this study, two types of high-entropy alloys (Fe-Mn-V-Cr-Al-C and Fe-Si-W-Cr-V) composed of low-radioactive elements (without Ni and Co) were prepared and their basic properties were evaluated for application as new functional materials to be used under radiation in high-energy accelerator target system components, nuclear reactors, fusion reactors, etc. and their basic properties were evaluated. The two materials under development in this study have unique properties in the following respects. The former is expected to be developed as a basic research for high-power motor materials as a new structural material and magnetic properties sharing the features of high strength and low radiation. On the other hand, the latter is expected to be applied as a new functional material in new engineering fields by mixing tungsten, which has the highest melting point among metallic elements, with vanadium, which has a considerably higher melting point, to raise the melting point of the alloy and to design an alloy with high strength.
Ikeda, Yoichi*; Umemoto, Yoshihiko*; Matsumura, Daiju; Tsuji, Takuya; Hashimoto, Yuki*; Kitazawa, Takafumi*; Fujita, Masaki*
Materials Transactions, 64(9), p.2254 - 2260, 2023/09
Times Cited Count：4 Percentile：31.44(Materials Science, Multidisciplinary)Yang, J.*; Ren, W.*; Zhao, X.*; Kikuchi, Tatsuya*; Miao, P.*; Nakajima, Kenji; Li, B.*; Zhang, Z.*
Journal of Materials Science & Technology, 99, p.55 - 60, 2022/02
Times Cited Count：14 Percentile：55.63(Materials Science, Multidisciplinary)High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices, differing from traditional alloys. Here, we investigate magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering. Direct-current (dc) and alternating-current (ac) magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions in the entire temperature region and three anomalies are found at about 80, 50, and 20 K, which are related to the paramagnetic to antiferromagnetic transition, the antiferromagnetic to ferromagnetic transition, and the spin freezing, respectively. The electrical and thermal conductivities are significantly reduced compared to Ni and the temperature dependence of lattice thermal conductivity exhibits a glass-like plateau. Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.
200 MeV ion irradiationPogrebnjak, A. D.*; Bagdasaryan, A. A.*; Horodeck, P.*; Tarelnyk, V.*; Buranich, V. V.*; Amekura, Hiroshi*; Okubo, Nariaki; Ishikawa, Norito; Beresnev, V. M.*
Materials Letters, 303, p.130548_1 - 130548_4, 2021/11
Times Cited Count：32 Percentile：84.67(Materials Science, Multidisciplinary)Positron annihilation spectroscopy (PAS) of ion-irradiated (TiZrHfNbV)N nitride which is a high-entropy alloy-based material indicates that the vacancy-defects are the dominant defects type. Although the specimens are irradiated up to 5
10
ions/cm
no amorphization or intermetallic phase formation is detected after the irradiation, demonstrating the radiation tolerance of the high-entropy alloys.
Naeem, M.*; Zhou, H.*; He, H.*; Harjo, S.; Kawasaki, Takuro; Lan, S.*; Wu, Z.*; Zhu, Y.*; Wang, X.-L.*
Applied Physics Letters, 119(13), p.131901_1 - 131901_7, 2021/09
Times Cited Count：22 Percentile：74.16(Physics, Applied)Lam, T.-N.*; Lee, S. Y.*; Tsou, N.-T.*; Chou, H.-S.*; Lai, B.-H.*; Chang, Y.-J.*; Feng, R.*; Kawasaki, Takuro; Harjo, S.; Liaw, P. K.*; et al.
Acta Materialia, 201, p.412 - 424, 2020/12
Times Cited Count：46 Percentile：88.47(Materials Science, Multidisciplinary)Lam, T.-N.*; Chou, Y.-S.*; Chang, Y.-J.*; Sui, T.-R.*; Yeh, A.-C.*; Harjo, S.; Lee, S. Y.*; Jain, J.*; Lai, B.-H.*; Huang, E.-W.*
Crystals (Internet), 9(8), p.420_1 - 420_8, 2019/08
Times Cited Count：10 Percentile：62.62(Crystallography)Yamashita, Shinichiro; Hashimoto, Naoyuki*; Oka, Hiroshi*
no journal, ,
In order to understand irradiation behavior of RA-MEA, CrFeMnNi alloy, up to the range of irradiation dose exceeding 100 dpa and demonstrate the applicability of AM to some of FCC single-phase nuclear materials, ion irradiation testing was performed. The conclusions obtained are as follows: In both microstructures of CrFeMnNi alloy prepared by conventional arc-melting or AM, a dense and fine cavity formed due to ion-irradiation over 200 dpa. However, estimated swellings (
V/V), which were calculated on the assumption that the thickness of all thin film samples is constant in this study, were 0.20% for arc-melted CrFeMnNi alloy and 0.63% for SLMed CrFeMnNi alloy, respectively. In the case of RA-MEAs, regardless of the difference in fabrication method, it was experimentally confirmed that RA-MEAs have high dimensional stability. In both microstructures of 316L after ion-irradiation over 200 dpa, void formation was confirmed. Void size distribution in SLMed 316L was quite different from that in arc-melted 316L, leading to the difference in estimated swellings between SLMed and arc-melted 316Ls; 0.52% (SLM) vs 6.61% (Arc-melting) This can be explained attributing to the difference in initial microstructure. Superior irradiation resistance in RA-MEA and Applicability of AM to nuclear structural materials were successfully confirmed.
Wakai, Eiichi; Noto, Hiroyuki*; Shibayama, Tamaki*; Nakagawa, Yuki*; Ishida, Taku*; Makimura, Shunsuke*; Wakui, Takashi; Furuya, Kazuyuki*; Ando, Masami*
no journal, ,
In the fields of energy, nuclear power, high-energy accelerator target systems, nuclear fusion, and biology, radiation causes degradation of materials and equipment, and thus it is expected to create new materials with high durability and superior functionality. In this study, for Fe-, Ti-, and W-based high-entropy alloys (HEA) composed of low activation elements (Ni and Co free), Fe-based alloys were prepared by radio frequency melting, Ti-based alloys by cold crucible levitation melting, and W-based alloys by arc melting using metal powders. These materials were tested by X-ray diffraction, microstructural observation, hardness measurement, magnetic measurement, electrical resistivity measurement, scanning transmission electron microscope STEM (or TEM, SEM) and energy dispersive X-ray spectroscopy, ultrasonic measurement, and hot isostatic pressing (HIP) method. These HEAs were found to be much harder than normal alloys, and in Fe-based HEAs, the magnetic properties and related microstructural analysis showed that they have interesting characteristics such as micro magnetic domain structures. In particular, for Fe- and W-based HEAs, the changes in crystal structure, orientation, and internal microstructure caused by HIP treatment and the accompanying effects of high temperature and pressure have been found to have a significant effect on magnetic properties and material strength properties.
Wakai, Eiichi; Noto, Hiroyuki*; Makimura, Shunsuke*; Ishida, Taku*; Furuya, Kazuyuki*; Shibayama, Tamaki*
no journal, ,
Recently, high-entropy alloys have been vigorously researched and developed by research institutes around the world because of their higher strength and ductility than conventional materials due to their atomic mixing ratio and composition. In this study, titanium-based high-entropy alloys (HEAs), TiVCrZrTa, TiVZrTaAl, and TiVCrZrW, were melted by the cold crucible surface melting method and subjected to homogenization heat treatment at 1200C for 5 hours. Mechanical property tests and properties of these HEAs were investigated, and it was found that the TiVCrZrTa HEAs have relatively better hot-rollability and hot-forgeability than other titanium-based HEAs. The Vickers hardness of these titanium-based HEAs was also found to be considerably higher than that of normal titanium alloys.
Suzuki, Kazuya; Takanashi, Koki
no journal, ,
High-entropy alloys (HEAs) have attracted considerable attention because of their excellent mechanical, heat-, corrosion-, and irradiation-resistance properties. Most studies have focused on their applications as structural materials. However, ferromagnetic HEAs may also exhibit excellent electromagnetic functions which are not observed in conventional alloys. In particular, new applications of HEAs are expected to develop by applying the fabrication method of highly structure-controlled nanolayered thin films, which is a specialty in the spintronics field. We focused on FeNiCoCuPd HEAs, which exhibit Curie temperatures higher than room temperature and contain Pd as a heavy metal with a large spin-orbit interaction In this study, we report the spin-dependent transport properties of FeNiCoCuPd thin films fabricated using a co-sputtering method.
Suzuki, Kazuya; Takanashi, Koki
no journal, ,
High-entropy alloys (HEAs) have attracted considerable attention because of their excellent functional properties such as mechanical, heat, corrosion, and irradiation resistance. In this study, we have focused on the basic spin-dependent transport properties of ferromagnetic FeNiCoCuPd with different compositions, such as the anisotropic magnetoresistance and anomalous Hall effects.
Suzuki, Kazuya; Takanashi, Koki
no journal, ,
High-entropy alloys (HEAs) consisting of more than five elements with disordered arrangements have attracted attention because of their excellent mechanical, heat, corrosion, and irradiation resistance properties. However, the spin-dependent transport properties of ferromagnetic HEAs have not yet been investigated in detail. In this study, we focused on the FeNiCoCuPd, which exhibits a high Curie temperature. Here, we report the anisotropic magnetoresistance effect (AMR) of FeNiCoCuPd thin films with different compositions.
Suzuki, Kazuya; Takanashi, Koki
no journal, ,
Fundamental properties and magnetoconductive properties of the ferromagnetic high-entropy alloy thin films (FeCoNiCuPd) prepared by sputtering were reported.
Isshiki, Hironari; Suzuki, Kazuya; Ieda, Junichi
no journal, ,
Suzuki, Kazuya
no journal, ,
High-entropy alloys (HEAs), composed of five or more elements in a disordered arrangement, are gaining attention for their excellent mechanical properties, thermal stability, corrosion resistance, and radiation tolerance. This presentation will detail the development of ferromagnetic HEAs for spintronics applications, and their potential uses at the Japan Atomic Energy Agency.
Wakai, Eiichi; Shibayama, Tamaki*; Noto, Hiroyuki*; Wakui, Takashi
no journal, ,
In this study, we fabricated a prototype iron-based high-entropy alloy (Fe-Mn-V-Cr-Al-C) composed of low activation elements (free of Ni and Co) by radio frequency melting method and evaluated its basic properties, aiming to apply it to new functional materials for high-energy accelerator target system components, nuclear reactors and fusion reactors. XRD analysis of this material revealed that it has a BCC crystal structure, in which vanadium carbide (VC) is precipitated. This material was found not only to be magnetic, but also to have a fairly small magnetic domain structure. As for the grain size, relatively small grains (about 20-50 m) were observed despite the homogenization heat treatment at 1150C. With regard to strength properties, the results of Vickers hardness measurements indicated that the alloy was much harder than ordinary iron alloys, slightly exceeding pure tungsten, and elastic wave velocity measurements showed that it was faster than iron-based materials and had a higher elastic modulus than stainless steel.
