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Wakai, Eiichi; Noto, Hiroyuki*; Kano, Sho*; Makimura, Shunsuke*; Ishida, Taku*; Shibayama, Tamaki*
no journal, ,
It is important for materials and devices that are subjected to high-energy particle beams to be able to withstand high thermal loads and irradiation. In this study, we investigated the irradiation resistance of nanoparticle-dispersed W (tungsten) and 1.1 wt% TiC-doped nanoparticle-dispersed W materials with a grain size of 1-2 
m and high strength, which were fabricated by mechanical alloying and high-temperature isostatic sintering. The irradiation was carried out at the HIT ion irradiation facility at the University of Tokyo at 773 K to about 0.7 dpa using tungsten ions, which are self ions. After the irradiation, the irradiation resistance of the materials was measured using a nanoindenter, and the results showed that the former material changed, while the latter material did not show any irradiation hardening.
Wakai, Eiichi; Noto, Hiroyuki*; Kano, Sho*; Ishida, Taku*; Makimura, Shunsuke*; Shibayama, Tamaki*
no journal, ,
It is important to develop materials that can withstand high heat load and irradiation, and to evaluate their safety and lifetime for materials and devices used under high intensity beam in high energy accelerators, and for fusion reactor wall materials and divertors near high temperature plasmas. Tungsten-based materials are candidates as target materials in the second target station project of the Materials and Life Science Experimental Facility at the J-PARC center. In this study, we investigated the irradiation resistance of the materials fabricated by mixing tungsten with TiC particles of about 1.1 wt%, mechanical alloying, and high-temperature isostatic sintering. This material is an innovative nanoparticle-dispersed W material with a crystal grain size of about 1 to 2 m and high strength. The irradiation resistance of this material and pure tungsten was examined by W ion irradiation at 773 K. These specimens were subjected to nanoindentation. These samples were analyzed by nanoindenter and transmission electron microscopy, and it was found for the first time that this nanoparticle-dispersed W material has a very high irradiation resistance compared to pure tungsten.
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 1150
C. 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.
Wakai, Eiichi; Noto, Hiroyuki*; Shibayama, Tamaki*; Iwamoto, Yosuke; Sato, Koichi*; Yano, Yukihiro*; Yoshikawa, Maya*; Nakagawa, Yuki*; Toyota, Kodai; Onizawa, Takashi
no journal, ,
In this study, we attempted to fabricate Fe-based and W-based Fe-HEA and W-HEA, both of which have been studied extensively in recent years to enhance the durability of equipment used in high-energy beam irradiation environments. For Fe-based HEAs, Fe-Mn-Cr-V-Al-C alloys were melted and casted, and then subjected to homogenization heat treatment (homogenization heat treatment (1150C for 2h)). After homogenization heat treatment, a 3-point bending test was performed at room temperature. The homogenization heat treatment resulted in an increase in ductility in the 3-point bending test and a decrease in elastic modulus based on ultrasonic velocity measurements. XRD measurements of this material after heat treatment (800C for 10 min and Water Quenched) showed that it has a BCC structure and a Vickers hardness that exceeds that of pure W. On the other hand, in the preparation of W-based HEA material (W-Fe-Si-V-Cr alloy), an arc melting method using powder was attempted, and it was found that an almost homogeneous crystallized alloy could be produced.
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; Shibayama, Tamaki*; Noto, Hiroyuki*; Furuya, Kazuyuki*; Iwamoto, Yosuke; Wakui, Takashi; Makimura, Shunsuke*; Ishida, Taku*; Ando, Masami*; Sato, Koichi*; et al.
no journal, ,
In fields such as nuclear power and high-energy accelerator target systems, radiation causes degradation of materials and equipment, so materials with high durability and excellent functionality are expected to be created. High-entropy alloys (HEA) are expected to have high irradiation resistance and often have high strength and good ductility. In recent years, research and development is underway worldwide for various applications. In this study, Fe- and Ti-based and W-based HEAs composed of low activation elements (free of Ni and Co) were fabricated. These materials were subjected to X-ray diffraction, microstructural observation, hardness, magnetism, electrical resistance, STEM (or TEM, SEM) and EDS, ultrasonic measurements, and hot isostatic pressing (HIP). Ion irradiation, pulsed laser irradiation, and pulsed electron beam irradiation were also performed on some of the samples to investigate their response characteristics. These HEAs were much harder than normal alloys, and the magnetic properties and related microstructural analysis of Fe-based HEAs revealed that they have interesting properties such as micro magnetic domain structures. In particular, for Fe- and W-based HEAs, the changes in crystal structure, orientation, and internal microstructure induced by HIP treatment and the accompanying effects of high temperature and pressure had a significant effect on magnetic properties and material strength properties. Furthermore, the irradiation response properties of Fe-based HEAs have been characterized.
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.
-phase based titanium alloysWakai, Eiichi; Ishida, Taku*; Kano, Sho*; Shibayama, Tamaki*; Sato, Koichi*; Noto, Hiroyuki*; Makimura, Shunsuke*; Furuya, Kazuyuki*; Yabuuchi, Atsushi*; Yoshiie, Toshimasa*; et al.
no journal, ,
Titanium materials have been applied to beam window materials and beam dumps in large accelerator systems because of their low specific gravity, high corrosion resistance, strength, and other advantages. As the beam power becomes higher, further improvement of irradiation resistance is required. We have investigated further the properties of titanium alloys based on the -phase, and it was found that Ti-15-3-3-3 alloys have excellent irradiation resistance when subjected to ion irradiation. In order to investigate the cause of this, microstructures and point defects in this and related materials were evaluated by TEM, positron lifetime measurement, electrical resistivity, and stress-induced changes, among others. In addition, we have recently begun to develop a prototype of a titanium-based high-entropy alloy based on -titanium, which is attracting worldwide attention and is being developed, and have also begun to evaluate the emotional properties of this alloy. We have examined the various properties of this material and found that it has considerably higher strength than conventional iron- and titanium-based materials.
Wakai, Eiichi; Noto, Hiroyuki*; Shibayama, Tamaki*; Iwamoto, Yosuke; Ishida, Taku*; Sato, Koichi*; Yabuuchi, Atsushi*; Yoshiie, Toshimasa*; Takahashi, Toshiharu*; Kobayashi, Yasuhiro*; et al.
no journal, ,
In recent years, it has been reported that high-entropy alloys (HEA) have high strength but good ductility, and they are being researched and developed by cutting-edge research institutions around the world with the aim of finding various applications in progress. In this study, we considered several Fe-based, W-based, and Ti-based HEAs, excluding Co and Ni elements, in order to aim for use in high radiation fields and considering low-activation properties. These materials mainly have a bcc crystal structure and were fabricated using a melting method and their material properties were evaluated. As a result, it was found that Fe-based HEA has properties that exceed the hardness of pure W and has excellent irradiation resistance. In addition, a Ti-based HEA that can be subjected to high-temperature forging and high-temperature rolling has been found, and evaluation of the optimal heat treatment temperature is progressing. The hardness of W-based HEA increased through Hot Isostatic Pressing (HIP) treatment, and it was found to have the world's highest hardness among HEA materials.