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Stacking fault driven phase transformation in CrCoNi medium entropy alloy

He, H.*; Naeem, M.*; Zhang, F.*; Zhao, Y.*; Harjo, S.; 川崎 卓郎; Wang, B.*; Wu, X.*; Lan, S.*; Wu, Z.*; et al.

Nano Letters, 21(3), p.1419 - 1426, 2021/02

 被引用回数:3 パーセンタイル:0(Chemistry, Multidisciplinary)

In CrCoNi, a so-called medium-entropy alloy, an fcc-to-hcp phase transformation has long been anticipated. Here, we report an in situ loading study with neutron diffraction, which revealed a bulk fcc-to-hcp phase transformation in CrCoNi at 15 K under tensile loading. By correlating deformation characteristics of the fcc phase with the development of the hcp phase, it is shown that the nucleation of the hcp phase was triggered by intrinsic stacking faults. The confirmation of a bulk phase transformation adds to the myriads of deformation mechanisms available in CrCoNi, which together underpin the unusually large ductility at low temperatures.


Enhancement of fatigue resistance by overload-induced deformation twinning in a CoCrFeMnNi high-entropy alloy

Lam, T.-N.*; Lee, S. Y.*; Tsou, N.-T.*; Chou, H.-S.*; Lai, B.-H.*; Chang, Y.-J.*; Feng, R.*; 川崎 卓郎; Harjo, S.; Liaw, P. K.*; et al.

Acta Materialia, 201, p.412 - 424, 2020/12

 被引用回数:13 パーセンタイル:92.23(Materials Science, Multidisciplinary)

We examined fatigue-crack-growth behaviors of CoCrFeMnNi high-entropy alloys (HEAs) under as-fatigued and tensile-overloaded conditions using neutron-diffraction measurements coupled with diffraction peak-profile analyses. We applied both high-resolution transmission electron microscopy (HRTEM) and neutron-diffraction strain mapping for the complementary microstructure examinations. Immediately after a single tensile overload, the crack-growth-retardation period was obtained by enhancing the fatigue resistance, as compared to the as-fatigued condition. The combined mechanisms of the overload-induced larger plastic deformation, the enlarged compressive residual stresses and plastic-zone size, the crack-tip blunting ahead of the crack tip, and deformation twinning governed the pronounced macroscopic crack-growth-retardation behavior following the tensile overload.


Element effects of Mn and Ge on the tuning of mechanical properties of high-entropy alloys

Lam, T.-N.*; Tsai, C.-W.*; Chen, B.-K.*; Lai, B.-H.*; Liu, H.-C*; 川崎 卓郎; Harjo, S.; Lin, B.-H.*; Huang, E.-W.*

Metallurgical and Materials Transactions A, 51(10), p.5023 - 5028, 2020/10

 被引用回数:3 パーセンタイル:59.43(Materials Science, Multidisciplinary)

Substitution of Ge for Mn increases the elastic moduli of different $${h k l}$$ orientations of the CoCrFeMnNi-based high-entropy alloy. Our findings indicate that tuning minor element compositions may result in improved strength-ductility combination. The underlying deformation mechanisms of CoCrFeNiGe$$_{0.3}$$ were examined by ${it in situ}$ neutron diffraction and analysis of the associated diffraction profiles during tensile deformation. The strain-hardening response of CoCrFeNiGe$$_{0.3}$$ exhibited a dominant mechanism of mechanical twinning at moderate and large strains at room temperature. The evolution of the bulk work hardening rate was consistent with the convolutional multiple whole profile fitting results, which exhibited a continuous increase in twin formation probability.


Work hardening, dislocation structure, and load partitioning in lath-martensite determined by ${it in situ}$ neutron diffraction line profile analysis

Harjo, S.; 川崎 卓郎; 友田 陽*; Gong, W.*; 相澤 一也; Tichy, G.*; Shi, Z.*; Ung$'a$r, T.*

Metallurgical and Materials Transactions A, 48(9), p.4080 - 4092, 2017/09


 被引用回数:22 パーセンタイル:84.2(Materials Science, Multidisciplinary)

${it in situ}$ neutron diffraction during tensile deformation of lath martensite steel containing 0.22 mass% of carbon, is performed using TAKUMI of J-PARC. The diffraction peaks at plastically deformed states exhibit asymmetries as the reflection of redistributions of the stress and dislocation densities/arrangements in lath-packets where the dislocation glides are favorable (soft packet) and unfavorable (hard packet). The dislocation density is as high as 10$$^{15}$$ m$$^{-2}$$ at the as-quenched state, and then during tensile straining, the load and the dislocation density become different between the two lath-packets. The dislocation character and arrangement vary also in the hard packet, but hardly change in the soft packet. The hard packet plays an important role in the high work hardening in martensite, which could be understood by taking into account not only the increase of the dislocation density but also the change in dislocation arrangement.


Composite behavior of lath martensite steels induced by plastic strain, a new paradigm for the elastic-plastic response of martensitic steels

Ung$'a$r, T.*; Harjo, S.; 川崎 卓郎; 友田 陽*; Rib$'a$rik, G.*; Shi, Z.*

Metallurgical and Materials Transactions A, 48(1), p.159 - 167, 2017/01


 被引用回数:25 パーセンタイル:86.24(Materials Science, Multidisciplinary)

Based on high-resolution neutron diffraction experiments we will show that in lath martensite steels the initially homogeneous dislocation structure is disrupted by plastic deformation, to produce a composite on the length scale of martensite lath packets. The diffraction patterns of plastically strained martensitic steel reveal characteristically asymmetric peak profiles in the same way as has been observed in materials with heterogeneous dislocation structures. Lath packets oriented favorably or unfavorably for dislocation glide become soft or hard. The lath packet type develops by work softening or work hardening in which the dislocation density becomes smaller or larger compared to the initial average one. The decomposition into soft and hard lath packets is accompanied by load redistribution between the two lath packet types. The composite behavior of plastically deformed lath martensite opens a new way to understand the elastic-plastic response in this class of materials.


Dislocation characteristics of martensitic steel studied by ${it in situ}$ neutron diffraction experiment

川崎 卓郎; Harjo, S.; Gong, W.; 相澤 一也; 岩橋 孝明; Shi, Z.*; Li, J.*; 友田 陽*; Ung$'a$r, T.*

JPS Conference Proceedings (Internet), 8, p.031009_1 - 031009_5, 2015/09

鉄鋼材料に代表される金属材料の力学的特性を理解するためには、弾性ひずみだけでなく、転位の密度や配列状態など微細構造を評価することが重要である。これらの情報はX線や中性子回折パターンに表れるBraggピークの形状を詳しく解析することで得ることができる。透過能の高い中性子を用いることでバルク状態の材料内部の微細構造に関する情報を得ることができるが、これまで中性子(特にパルス中性子)はあまり適用されてこなかった。我々はJ-PARC物質生命科学実験施設BL19に設置された工学材料回折装置 匠を用いてマルテンサイト鋼の引張り試験その場中性子回折測定を行い、CMWP法と呼ばれる解析法を用いてこの材料の微細構造を調べた。その結果、巨視的なひずみの増加に伴う転位密度の増加は比較的小さく、転位配列の顕著な規則化が観測された。


Progress of the ITER central solenoid model coil programme

辻 博史; 奥野 清*; Thome, R.*; Salpietro, E.*; Egorov, S. A.*; Martovetsky, N.*; Ricci, M.*; Zanino, R.*; Zahn, G.*; Martinez, A.*; et al.

Nuclear Fusion, 41(5), p.645 - 651, 2001/05

 被引用回数:55 パーセンタイル:84.47(Physics, Fluids & Plasmas)



Trial fabrication of heavy section base metals and welded joints for ITER TF coil

石尾 光太郎*; 中嶋 秀夫; 布谷 嘉彦; 三浦 友史; 川崎 勉*; 辻 博史

Advances in Cryogenic Engineering Materials, 44, p.73 - 80, 1998/00



SMESモデル・コイル; 初期冷凍・熱特性

濱田 一弥; 加藤 崇; 河野 勝己; 本田 忠明*; 種田 雅信*; 関口 修一*; 今橋 浩一*; 大都 起一*; 田尻 二三男*; 大内 猛*; et al.

低温工学, 33(7), p.467 - 472, 1998/00

SEMSモデル・コイルは、強制冷凍型導体を使用した4層ダブルパンケーキのコイルで、全質量は4.5トンである。ITER CSモデルコイル用に開発された冷凍機を用いて、コイルに過大な熱歪みを加えぬよう感度制御しながら初期冷凍を行い、目標である10日以内に初期冷凍を終了した。熱負荷を測定したところ、7.5Wであり、設計値と比較して同程度であった。


Mechanical properties of 110mm thick hot rolled plates of JJ1 and JK2 for ITER TF coil

石尾 光太郎*; 中嶋 秀夫; 川崎 勉*; 上原 聡明*; 辻 博史; F.Wong*; 島本 進*

Proc. of 15th Int. Conf. on Magnet Technology (MT-15), p.989 - 992, 1997/10



Development of high strength austenitic stainless steel for conduit of Nb$$_{3}$$Al conductor

中嶋 秀夫; 布谷 嘉彦; O.Ivano*; 安藤 俊就; 川崎 勉*; 塙 博美*; 関 秀一*; 高野 克敏*; 辻 博史; 佐藤 雄一*; et al.

Advances in Cryogenic Engineering Materials, Vol.42, p.323 - 330, 1996/00



In situ neutron diffraction monitoring on transformation and tensile behavior of lath martensite

Harjo, S.; Gong, W.; 川崎 卓郎; 諸岡 聡; 山下 享介*; 友田 陽*; Ung$"a$r, T.*

no journal, , 

In situ neutron diffraction was used to monitor martensitic transformation during cooling for a Fe-18Ni alloy and tensile behavior of martensite for a 22SiMn2TiB steel. Changes in the lattice parameters of austenite and martensite in the Fe-18Ni alloy during cooling, were used to discuss the phase stress formed by martensitic transformation. Changes in the dislocation density, character and arrangement of martensite during tensile loading in the 22SiMn2TiB steel were used to discuss the deformation mechanism of martensite steel.

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