Faculty Profiles - TOKUNAGA Tatsuya

Papers - TOKUNAGA Tatsuya

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Microstructure and Phase Transformation in Fe20Co20Ni20Cr20B20-xSix Alloys Prepared by Mechanical Alloying Reviewed International journal

Yicheng Zhang, Manabu Ishimaru, Tatsuya Tokunaga, Hidenori Era

Materials Transactions ( Japan Institute of Metals and Materials ) 64 ( 11 ) 2568 - 2574 2023.11

Structure and Magnetic Properties of Mn-Pt and Mn-Pt-B Melt-Spun Ribbons Reviewed International journal

Mayu Mitsue, Iwao Sasaki, Yicheng Zhang, Tatsuya Tokunaga, Toshifumi Ogawa

2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings ( Institute of Electrical and Electronics Engineers Inc. ) 2023.05

急冷凝固したFeCoNiCrBSi合金におけるミクロ組織とガラス形成 Reviewed

張亦成,　徳永辰也

材料 72 ( 3 ) 231 - 233 2023.03

α鉄におけるホウ素，炭素の粒界偏析に及ぼす合金元素の影響 Reviewed

徳永辰也 , 元村優太, 恵良秀則, 土山聡宏, 菖蒲一久, 長谷部光弘, 大谷博司

鉄と鋼 109 ( 3 ) 158 - 166 2023.03

Microstructure control and its observation of rapid solidification Cu–La alloy for the development of fluoride-ion batteries Reviewed International journal

S. Zhu, H. Akamine, Y. Nagahata, T. Tojigamori, H. Miki, Y. Zhang, T. Tokunaga, S. Iikubo

Journal of Alloys and Compounds 930 167447 2023.01

Thermodynamic calculation of phase equilibria in the Al-Fe-Zn-O system Reviewed International journal

Matsumoto N., Tokunaga T.

High Temperature Materials and Processes 41 ( 1 ) 605 - 620 2022.12

Investigation of Nanoscale Phase Formation in Rapidly Solidified Fe20Co20Ni20Cr20B201xSix Alloys Reviewed International journal

Zhang Yicheng, Inoue Koji, Ishimaru Manabu, Tokunaga Tatsuya, Era Hidenori

MATERIALS TRANSACTIONS ( The Japan Institute of Metals and Materials ) 63 ( 9 ) 1211 - 1216 2022.09

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)

In this study, nanoscale phase formation in rapidly solidified Fe20Co20Ni20Cr20B20−xSix alloys was investigated using atom probe tomography (APT) and transmission electron microscopy (TEM). According to previous X-ray diffraction measurements and scanning electron microscopy with energy-dispersive X-ray spectroscopy results, it was thought that this alloy system was composed of almost a single face-centered cubic (FCC) solid solution phase when the Si content was 5 at.%. However, APT and TEM results at the nanoscale showed that both an FCC solid solution and compound phases formed for all alloy compositions. The rapidly solidified alloy ribbon with a Si content of 5 at.% showed the presence of nanoscale FCC and Cr2B phases. Furthermore, in addition to the nanoscale FCC and Cr2B phases, a nanoscale Cr3Ni5Si2 phase was observed when the Si content exceeded 7.5 at.%.

DOI： 10.2320/matertrans.mt-m2022058

CiNii Research

鋼中における溶質元素の粒界偏析の熱力学的評価 Invited

徳永辰也

フジコー技報 ( 株式会社フジコー ) 29 6 - 10 2021.12

Fe20Co20Ni20Cr20B20-xSixハイエントロピー合金の形成相に及ぼす冷却速度の影響と加熱による相変態挙動 Reviewed

張亦成, 徳永辰也, 恵良秀則, 菖蒲一久, 長谷部光弘

鋳造工学 ( 日本鋳造工学会 ) 93 ( 9 ) 532 - 540 2021.09

α鉄中における窒素の粒界偏析に及ぼす合金元素の影響 Reviewed

元村優太, 徳永辰也, 恵良秀則, 菖蒲一久, 長谷部光弘, 大谷博司

熱処理 ( 日本熱処理技術協会 ) 61 ( 3 ) 119 - 125 2021.06

溶湯浸透法によって作製したSiC二段反応焼結体の摩耗特性 Reviewed

花田喜嗣, 肖陽, 徳永辰也, 恵良秀則

鋳造工学 92 ( 9 ) 469 - 476 2020.09

Rapid fabrication of the continuous AlFeCrCoNi high entropy alloy coating on aluminum alloy by resistance seam welding Reviewed

Zhao D., Yamaguchi T., Shu J., Tokunaga T., Danjo T.

Applied Surface Science 517 2020.07

Language：English Publishing type：Research paper (scientific journal)

The continuous AlFeCrCoNi high entropy alloy coating was firstly fabricated on aluminium alloy by resistance seam welding. During welding, the coating was formed rapidly under the effect of instantaneous joule heating and the pressure. The gradient temperature transformed the nanocrystalline AlFeCrCoNi powder into the AlFeCrCoNi HEA coating consisted of body-centered-cubic and face-centered cubic structures. According to the calculation and experimental results, the welding process was not brought the negative affect to the substrate and only a certain amount of aluminum element penetrated into the coating. The average thickness and hardness of the coating were 420 µm and 715HV , respectively. Compared to A6061, the coating exhibited excellent wear-resistance in dry, deionized water and 3.5 wt% NaCl solution conditions. The environment played an important role in the wear behaviour of the AlFeCrCoNi HEA coating. Meanwhile, the corrosive wear of the AlFeCrCoNi HEA coating was proved to be beneficial to reduce the wear rate. 0.2

DOI： 10.1016/j.apsusc.2020.145980

Scopus

Other Link： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85082708091&origin=inward

Effect of Fe-Si Alloy Composition on Mechanical Properties and Electrical Resistivity of Sintered SiC Ceramics Fabricated by Melt Infiltration Method Reviewed

Hanada Yoshitsugu, Sho Yo, Yamamoto Atsuo, Tokunaga Tatsuya, Era Hidenori

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 92 ( 1 ) 8 - 15 2020.01

Language：Japanese Publishing type：Research paper (scientific journal)

The authors have been investigating a fabrication method to obtain high performance SiC ceramics by two-step reaction sintering using a Fe-Si alloy that is well known as an inoculation agent. In this study, compositions of C as a constituent of first-sintered body and the Fe-Si alloy as a constituent of molten infiltration alloy for the second sintering were changed for SiC ceramics fabrication. The second-sintered body was fabricated by infiltrating the Fe-Si molten alloy into the porous first-sintered body at 1723 K for 6 h under a pressure lower than 10-2 Pa. The C content for the first sintered body was changed from 0 to 28 mass%, whereas the Fe concentration of the alloy for infiltration was changed from 0 to 66 mass%. Microstructure observation, elemental distribution measurements of Fe and Si, and phase identification for obtained second-sintered specimens were conducted using a laser microscope, EPMA, and XRD, respectively. Hardness and fracture toughness were evaluated by results of micro Vickers hardness testing. The electrical resistivity was measured using the four-terminal method. The microstructure of sintered SiC changed with the Fe content of the infiltration alloy, whereas the generated amount of SiC changed only slightly irrespective of the Fe content. No Fe carbide formation was observed, but FeSi2 and FeSi phases were formed at high Fe contents. The fracture toughness of sintered bodies improved to 5.9 MPa·m0.5 at maximum by the increase in the C content of the first sintered body and the Fe content of the infiltration alloy, although the electrical resistivity was reduced to 1.5 × 10-5 Ωm at the minimum by the increase in Fe contents. Consequently, the fracture toughness of the Fe-Si alloy infiltrated SiC improved by two times compared to the conventionally sintered SiC ceramics. Furthermore, the electrical resistivity of the SiC sample largely decreased by one digit or more. It is considered that the superior characteristics are brought about by the extensive formation of finely distributed FeSi2 and FeSi phases.

DOI： 10.11279/jfes.92.8

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/130007793406

Silicon Carbide Fabrication by Infiltration of Molten Fe-Si Alloy Through Two-Step Reaction Sintering Reviewed International journal

Yoshitsugu Hanada, Yang Xiao, Akio Sonoda, Hyo-Gyoung Kang,Hideaki Nagayoshi, Atsuo Yamamoto, Tatsuya Tokunaga

Archives of Metallurgy and Materials 64 ( 4 ) 1645 - 1652 2019.12

Fabrication and Mechanical Properties of Reaction Sintered SiC Ceramics by Infiltration of Fe-75%Si Alloy Melt Reviewed

Hanada Yoshitsugu, Sho Yo, Yamamoto Atsuo, Tokunaga Tatsuya, Era Hidenori

Journal of Japan Foundry Engineering Society ( Japan Foundry Engineering Society ) 91 ( 10 ) 710 - 716 2019.10

Language：Japanese Publishing type：Research paper (scientific journal)

Structure and mechanical properties of SiC fabricated by the reaction sintering method have been investigated by varying the blending composition of Si, C and SiC powders. First, specimens of the first-sintered body were formed at 473 K under a pressure of 20 MPa in a metallic mold and then sintered by heating at 973 K for 3.6 ks in Ar gas atmosphere. The first-sintered specimens were next put into a graphite mold to set Fe-75mass%Si alloy, which is often used as an inoculation agent, on the specimens and then held at 1693 K for 900 s in a vacuum furnace under a pressure of 10-1 Pa. Finally, SiC was successfully performed as a second-sintered body through the infiltration of Fe-75%Si alloy melt into the porous first-sintered body, which was followed by their mutual reaction. The microstructure and distributions of Fe and Si elements were observed using laser microscope and EPMA respectively. The hardness and fracture toughness were measured using a micro-Vickers hardness tester. The results indicate good infiltration of Fe-75%Si alloy melt into the first sintered body and that the second sintered body had a small amount of porosity. Iron carbides could not be found in the sintered structure but finely distributed iron silicides of FeSi and FeSi2 were found. Furthermore, the fracture toughness of the body increased with increasing C content in the first sintered body. The mechanical properties were improved more than that of conventional sintered SiC when Fe-Si alloy was employed. The improvement in the properties is thought to be due to the uniform and fine distribution of FeSi, FeSi2 and SiC in the matrix.

DOI： 10.11279/jfes.91.710

CiNii Article

Other Link： https://ci.nii.ac.jp/naid/130007740200

Effect of Nickel Content on Microstructural Evolution in Austempered Solution-Strengthened Ferritic Ductile Cast Iron Reviewed International journal

Tokunaga T., Kim Y., Era H.

Journal of Materials Engineering and Performance 28 ( 7 ) 4034 - 4040 2019.07

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

© 2019, ASM International. The effects of Ni content and austempering temperature on microstructural evolution during austempering in solution-strengthened ferritic ductile cast iron with Ni contents between 0 and 1.1 mass% were investigated. The microstructure observation for the samples austempered at temperatures between 375 and 325 °C using an infrared gold image furnace was carried out with optical microscopy, x-ray diffraction measurements, and electron back-scattered diffraction pattern (EBSP) analysis. In addition, the Vickers hardness of both the austempered and as-quenched samples was measured under a load of 0.9807 N. According to the microstructure observations, the matrix of the samples austempered at temperatures between 375 and 325 °C exhibited finer acicular ferrite microstructure with increasing Ni content. Optical microscopy and EBSP analysis revealed that the amount of high-carbon austenite phase for the austempered samples increased with increasing Ni content and austempering temperature. Although samples with higher Ni content were found to contain more high-carbon austenite phase in the matrix, the Vickers hardness of the samples tended to increase with increasing Ni content at the same austempering temperature. The reason for this may be the higher carbon content in the matrix of the samples with higher Ni contents.

DOI： 10.1007/s11665-019-04184-y

Scopus

Other Link： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85068872076&origin=inward

Fabrication method of silicon carbide by infiltration of molten Fe-Si alloy through two-step reaction sintering Reviewed

Hanada Y., Xiao Y., Sonoda A., Kang H.G., Nagayoshi H., Tokunaga T., Era H.

73rd World Foundry Congress &quot;Creative Foundry&quot;, WFC 2018 - Proceedings 161 - 162 2018.09

Effect of nickle content on microstructural evolution in austempered solution strengthened ferritic ductile cast iron Reviewed

Tokunaga T., Kim Y., Era H.

73rd World Foundry Congress &quot;Creative Foundry&quot;, WFC 2018 - Proceedings 191 - 192 2018.09

Language：English Publishing type：Research paper (international conference proceedings)

The effects of Ni content and austempering temperature on the microstructural evolution during austempering in SSFDI with different Ni contents were investigated. The results obtained are summarized as follows: (1) The bainitic ferrite microstructure for SSFDI was found to be much coarser with increasing Ni content. (2) The amounts of retained austenite for the samples after austempering increased with increasing Ni content and austempering temperature. (3) The Vickers hardness of the matrix for each sample decreased with the increase in austempering temperature, in contrast, increased with increasing Ni content.

Scopus

Other Link： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85062279167&origin=inward

状態図計算と金属溶射プロセスへの応用 Invited Reviewed

徳永辰也，曽珍素，恵良秀則

溶射 55 ( 2 ) 80 - 84 2018.04

Effect of cooling rate after fusing on the microstructural evolution and hardness of a Co-based self-fluxing alloy

2 pages 2017.11

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Papers - TOKUNAGA Tatsuya