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論文

Pressure-modulated magnetism and negative thermal expansion in the Ho$$_2$$Fe$$_{17}$$ intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; 加藤 健一*; 服部 高典; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

https://doi.org/10.1021/acs.chemmater.3c00158

静水圧や化学圧力は、結晶構造を変化させる効率的な刺激であり、材料科学において電気的、磁気的特性のチューニングによく利用されている。しかし、化学圧力は定量化が困難であり、これら両者の定量的な対応関係はまだよくわかっていない。本研究では、負の熱膨張(NTE)を持つ永久磁石の候補である金属間化合物を調べた。放射光X線その場観察により、AlをドープしたHo$$_2$$Fe$$_{17}$$に負の化学圧力があることを明らかにし、単位セル体積の温度・圧力依存性を用いそれを定量的に評価した。また、磁化測定と中性子回折測定を組み合わせることで、磁気秩序に対する化学圧力と静水圧の違いを比較した。興味深いことに、圧力はNTEの抑制と増強を制御するために使用することができた。電子状態計算から、圧力がFermiレベル(EF)に対する主要バンドの上部に影響を与えたことを示しており、これは磁気安定性に影響を与え、それが磁気とNTEを調節する上で重要な役割を果たしていることがわかった。本研究は、圧力の影響を理解し、それを利用して機能性材料の特性を制御する良い例を示している。

論文

Multiple mechanisms in proton-induced nucleon removal at $$sim$$100 MeV/nucleon

Pohl, T.*; Sun, Y. L.*; Obertelli, A.*; Lee, J.*; G$'o$mez-Ramos, M.*; 緒方 一介*; 吉田 数貴; Cai, B. S.*; Yuan, C. X.*; Brown, B. A.*; et al.

Physical Review Letters, 130(17), p.172501_1 - 172501_8, 2023/04

https://doi.org/10.1103/PhysRevLett.130.172501

大きなフェルミ面非対称性を持つ陽子過剰な$$^{14}$$O原子核からの100MeV/nucleonでの陽子による陽子・中性子除去反応について報告した。この結果は、quasi-freeノックアウト反応、非弾性散乱、核子移行反応を含む複数の反応機構の定量的寄与を初めて示すものである。このようなエネルギー領域では通常無視される非弾性散乱と核子移行の寄与が、弱束縛陽子と強束縛中性子の除去反応断面積にそれぞれ約50%と30%寄与していることが示された。

論文

Tensile overload-induced texture effects on the fatigue resistance of a CoCrFeMnNi high-entropy alloy

Lam, T.-N.*; Chin, H.-H.*; Zhang, X.*; Feng, R.*; Wang, H.*; Chiang, C.-Y.*; Lee, S. Y.*; 川崎 卓郎; Harjo S.; Liaw, P. K.*; et al.

Acta Materialia, 245, p.118585_1 - 118585_9, 2023/02

https://doi.org/10.1016/j.actamat.2022.118585
 被引用回数：1 パーセンタイル：0(Materials Science, Multidisciplinary)

The present study investigates the crystallographic-texture effects on the improved fatigue resistance in the CoCrFeMnNi high-entropy alloys (HEAs) with the full-size geometry of the ASTM Standards E647-99. We exploited X-ray nano-diffraction mapping to characterize the crystal-deformation levels ahead of the crack tip after stress unloading under both constant- and tensile overloaded-fatigue conditions. The crack-tip blunting-induced much higher deformation level was concentrated surrounding the crack-tip which delays the fatigue-crack growth immediately after a tensile overload. The predominant deformation texture orientation in the Paris regime was investigated, using electron backscatter diffraction and orientation distribution function analyses. The twinning formation-driven shear deformation gave rise to the development of the Goss-type texture within the plastic deformation regime under a tensile-overloaded-fatigue condition, which was attributed to enhance the crack deflection and thus the tensile induced crack-growth-retardation period in the CoCrFeMnNi HEA.

論文

Study of the $$N=32$$ and $$N=34$$ shell gap for Ti and V by the first high-precision multireflection time-of-flight mass measurements at BigRIPS-SLOWRI

飯村 俊*; Rosenbusch, M.*; 高峰 愛子*; 角田 佑介*; 和田 道治*; Chen, S.*; Hou, D. S.*; Xian, W.*; 石山 博恒*; Yan, S.*; et al.

Physical Review Letters, 130(1), p.012501_1 - 012501_6, 2023/01

https://doi.org/10.1103/PhysRevLett.130.012501

The atomic masses of $$^{55}$$Sc, $$^{56,58}$$Ti, and $$^{56-59}$$V have been determined using the high-precision multireflection time-of-flight technique. The radioisotopes have been produced at RIKEN's Radioactive Isotope Beam Factory (RIBF) and delivered to the novel designed gas cell and multireflection system, which has been recently commissioned downstream of the ZeroDegree spectrometer following the BigRIPS separator. For $$^{56,58}$$Ti and $$^{56-59}$$V, the mass uncertainties have been reduced down to the order of 10 keV, shedding new light on the $$N=34$$ shell effect in Ti and V isotopes by the first high-precision mass measurements of the critical species $$^{58}$$Ti and $$^{59}$$V. With the new precision achieved, we reveal the nonexistence of the $$N=34$$ empirical two-neutron shell gaps for Ti and V, and the enhanced energy gap above the occupied $$nu$$p$$_{3/2}$$ orbit is identified as a feature unique to Ca. We perform new Monte Carlo shell model calculations including the $$nu$$d$$_{5/2}$$ and $$nu$$g$$_{9/2}$$ orbits and compare the results with conventional shell model calculations, which exclude the $$nu$$g$$_{9/2}$$ and the $$nu$$d$$_{5/2}$$ orbits. The comparison indicates that the shell gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at $$N = 34$$.

論文

Laser-driven neutron generation realizing single-shot resonance spectroscopy

余語 覚文*; Lan, Z.*; 有川 安信*; 安部 勇輝*; Mirfayzi, S. R.*; Wei, T.*; 森 隆人*; Golovin, D.*; 早川 岳人*; 岩田 夏弥*; et al.

Physical Review X, 13(1), p.011011_1 - 011011_12, 2023/01

https://doi.org/10.1103/PhysRevX.13.011011
 被引用回数：0 パーセンタイル：0.02(Physics, Multidisciplinary)

Neutrons are powerful tools for investigating the structure and properties of materials used in science and technology. Recently, laser-driven neutron sources (LDNS) have attracted the attention of different communities, from science to industry, in a variety of applications, including radiography, spectroscopy, security, and medicine. However, the laser-driven ion acceleration mechanism for neutron generation and for establishing the scaling law on the neutron yield is essential to improve the feasibility of LDNS. In this paper, we report the mechanism that accelerates ions with spectra suitable for neutron generation. We show that the neutron yield increases with the fourth power of the laser intensity, resulting in the neutron generation of $$3times10^{11}$$ in $$4pi$$ at a maximum, with $$1.1times10^{19}$$ Wcm$$^{-2}$$, 900 J, 1.5 ps lasers. By installing a "hand-size" moderator, which is specially designed for the LDNS, it is demonstrated that the efficient generation of epithermal (0.1-100 eV) neutrons enables the single-shot analysis of composite materials by neutron resonance transmission analysis (NRTA). We achieve the energy resolution of 2.3% for 5.19-eV neutrons 1.8 m downstream of the LDNS. This leads to the analysis of elements and isotopes within sub-$$mu$$s times and allows for high-speed nondestructive inspection.

論文

Si-addition contributes to overcoming the strength-ductility trade-off in high-entropy alloys

Wei, D.*; Gong, W.; 都留 智仁; Lobzenko, I.; Li, X.*; Harjo S.; 川崎 卓郎; Do, H.-S.*; Bae, J. W.*; Wagner, C.*; et al.

International Journal of Plasticity, 159, p.103443_1 - 103443_18, 2022/12

https://doi.org/10.1016/j.ijplas.2022.103443
 被引用回数：6 パーセンタイル：95.02(Engineering, Mechanical)

Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.

論文

"Southwestern" boundary of the $$N = 40$$ island of inversion; First study of low-lying bound excited states in $$^{59}$$V and $$^{61}$$V

Elekes, Z.*; Juh$'a$sz, M. M.*; Sohler, D.*; Sieja, K.*; 吉田 数貴; 緒方 一介*; Doornenbal, P.*; Obertelli, A.*; Achouri, N. L.*; 馬場 秀忠*; et al.

Physical Review C, 106(6), p.064321_1 - 064321_10, 2022/12

https://doi.org/10.1103/PhysRevC.106.064321
 被引用回数：0 パーセンタイル：0.02(Physics, Nuclear)

$$^{59}$$Vと$$^{61}$$Vの低励起準位構造を初めて探索した。$$^{61}$$Vについては中性子ノックアウト反応と陽子非弾性散乱が、$$^{59}$$Vについては中性子ノックアウト反応データが得られた。$$^{59}$$Vについては4つ、$$^{61}$$Vについては5つの新たな遷移が確認された。Lenzi-Nowacki-Poves-Sieja (LNPS)相互作用に基づく殻模型計算との比較によって、それぞれの同位体について確認されたガンマ線のうち3つが、first 11/2$$^{-}$$状態とfirst 9/2$$^{-}$$状態からの崩壊と決定された。$$^{61}$$Vについては、($$p$$,$$p'$$)非弾性散乱断面積は四重極変形と十六重極変形を想定したチャネル結合法により解析されたが、十六重極変形の影響により、明確に反転の島に属するとは決定できなかった。

論文

Extended $$p_{3/2}$$ neutron orbital and the $$N = 32$$ shell closure in $$^{52}$$Ca

Enciu, M.*; Liu, H. N.*; Obertelli, A.*; Doornenbal, P.*; Nowacki, F.*; 緒方 一介*; Poves, A.*; 吉田 数貴; Achouri, N. L.*; 馬場 秀忠*; et al.

Physical Review Letters, 129(26), p.262501_1 - 262501_7, 2022/12

https://doi.org/10.1103/PhysRevLett.129.262501
 被引用回数：0 パーセンタイル：0(Physics, Multidisciplinary)

$$sim$$230MeV/nucleonでの$$^{52}$$Caからの中性子ノックアウト反応が$$gamma$$線分光と行われ、$$1f_{7/2}$$と$$2p_{3/2}$$軌道からの中性子ノックアウト反応の運動量分布が測定された。断面積は$$N=32$$の閉殻と整合し、Ca同位体での$$N=28$$と$$N=34$$閉殻と同程度に強い閉殻であることが確認された。運動量分布の分析から$$1_{f7/2}$$と$$2p_{3/2}$$軌道の平均二乗根半径の差は0.61(23)fmと決定され、これはmodified-shell-modelによる予言の0.7fmと整合した。これは、中性子過剰なCa同位体での$$2p_{3/2}$$軌道半径が大きいことが、中性子数にしたがって線形的に荷電半径が増える意外な現象の原因であることを示唆している。

論文

Stress contribution of B2 phase in Al$$_{0.7}$$CoCrFeNi eutectic high entropy alloy

Yun, D.*; Chae, H.*; Lee, T.*; Lee, D.-H.*; Ryu, H. J.*; Banerjee, R.*; Harjo S.; 川崎 卓郎; Lee, S. Y.*

Journal of Alloys and Compounds, 918, p.165673_1 - 165673_7, 2022/10

https://doi.org/10.1016/j.jallcom.2022.165673
 被引用回数：0 パーセンタイル：0(Chemistry, Physical)

In this study, the deformation behavior and strengthening contribution of the FCC phase and B2 phase in Al$$_{0.7}$$CoCrFeNi eutectic high entropy alloys (HEAs) were investigated using in-situ neutron diffraction. An FCC matrix phase exhibited a slip-dominant deformation scheme, while twinning hardly contributed to deformation. Applied macroscopic stresses were rarely redistributed to the BCC A2 phase dispersed within the B2 phase, whereas the stress contribution of the B2 phase, which was initially lower than that of the FCC phase, increased significantly with an increase in plastic strain; hence, its contribution to tensile deformation became predominant. This study allows us to postulate a target value of each phase by microstructural tunning to achieve the desired properties of multicomponent phase HEAs.

論文

Estimating fine melt pool, coarse melt pool, and heat affected zone effects on the strengths of additive manufactured AlSi10Mg alloys

Lam, T.-N.*; Lee, A.*; Chiu, Y.-R.*; Kuo, H.-F.*; 川崎 卓郎; Harjo S.; Jain, J.*; Lee, S. Y.*; Huang, E.-W.*

Materials Science & Engineering A, 856, p.143961_1 - 143961_9, 2022/10

https://doi.org/10.1016/j.msea.2022.143961
 被引用回数：1 パーセンタイル：48.61(Nanoscience & Nanotechnology)

Fine melt pool (FMP), coarse melt pool (CMP), and heat affected zone (HAZ) are generally observed in the additive manufactured AlSi10Mg alloys. In this study, we demonstrated that the yield strength can be estimated by the combination of the sizes and volume fractions of FMP, CMP, HAZ together with the second-phase hardening. Two different AlSi10Mg alloys fabricated via powder bed fusion (PBF) process were prepared to examine the lattice strain evolution of constituent phases during uniaxial tensile loading via in-situ neutron diffraction measurements. The horizontally-built (Hz-built) exhibited a much better yield and tensile strength as well as elongation compared to the vertically-built (Vt-built) AlSi10Mg alloy. We reported empirical strength quantification based on the sizes and ratios of fine melt pool (FMP), coarse melt pool (CMP), and heat affected zone (HAZ) together with the possible failure mode to prevent early fracture in the additive manufactured alloys.

論文

Selective recovery of thorium and uranium from leach solutions of rare earth concentrates in continuous solvent extraction mode with primary amine N1923

Nguyen, T. H.*; Le Ba, T.*; Tran, C. T.*; Nguyen, T. T.*; Doan, T. T. T.*; Do, V. K.; 渡邉 雅之; Pham, Q. M.*; Hoang, S. T.*; Nguyen, D. V.*; et al.

Hydrometallurgy, 213, p.105933_1 - 105933_11, 2022/08

https://doi.org/10.1016/j.hydromet.2022.105933
 被引用回数：2 パーセンタイル：48.61(Metallurgy & Metallurgical Engineering)

ベトナム・イェンフー希土類精鉱浸出液からトリウム(Th)とウラン(U)を選択的に回収するための連続向流抽出法を系統的に研究した。抽出剤としては、イソパラフィンIP-2028希釈液で調製した一級アミンN1923を用いた。トリウムとウランは、連続ミキサーセトラエクストラクション,スクラビング,逆エクストラクションによって確立された湿式製錬サイクルで選択的に回収され、ラボスケールで実施された。有機相と水相の体積比(O/A比)を管理することにより、ThとUの所望の純度を達成することができる。逆抽出液とラフィネートからそれぞれ高純度のThとUを回収することができ、その後の核物質処理に十分な特性を有している。

論文

$$phi$$ meson properties in nuclear matter from QCD sum rules with chirally separated four-quark condensates

Kim, J.*; Gubler, P.; Lee, S. H.*

Physical Review D, 105(11), p.114053_1 - 114053_9, 2022/06

https://doi.org/10.1103/PhysRevD.105.114053
 被引用回数：0 パーセンタイル：0.01(Astronomy & Astrophysics)

The modification of the $$phi$$ meson spectrum in nuclear matter is studied in an updated QCD sum rule analysis, taking into account recent improvements in properly treating the chiral invariant and breaking components of four-quark condensates. Allowing both mass and decay width to change at finite density, the QCD sum rule analysis determines certain combinations of changes for these parameters that satisfy the sum rules equally well. A comprehensive error analysis, including uncertainties related to the behavior of various condensates at linear order in density, the employed renormalization scale and perturbative corrections of the Wilson coefficients, is used to compute the allowed ranges of these parameter combinations. We find that the $$phi$$ meson mass shift in nuclear matter is especially sensitive to the strange sigma term $$sigma_{sN}$$, which determines the decrease of the strange quark condensate in nuclear matter.

論文

Status of the uncertainty quantification for severe accident sequences of different NPP-designs in the frame of the H-2020 project MUSA

Brumm, S.*; Gabrielli, F.*; Sanchez-Espinoza, V.*; Groudev, P.*; Ou, P.*; Zhang, W.*; Malkhasyan, A.*; Bocanegra, R.*; Herranz, L. E.*; Berda$"i$, M.*; et al.

Proceedings of 10th European Review Meeting on Severe Accident Research (ERMSAR 2022) (Internet), 13 Pages, 2022/05

The current HORIZON-2020 project on "Management and Uncertainties of Severe Accidents (MUSA)" aims at applying Uncertainty Quantification (UQ) in the modeling of Severe Accidents (SA), particularly in predicting the radiological source term of mitigated and unmitigated accident scenarios. Within its application part, the project is devoted to the uncertainty quantification of different severe accident codes when predicting the radiological source term of selected severe accident sequences of different nuclear power plant designs, e.g. PWR, VVER, and BWR. Key steps for this investigation are, (a) the selection of severe accident sequences for each reactor design, (b) the development of a reference input model for the specific design and SA-code, (c) the selection of a list of uncertain model parameters to be investigated, (d) the choice of an UQ-tool e.g. DAKOTA, SUSA, URANIE, etc., (e) the definition of the figures of merit for the UA-analysis, (f) the performance of the simulations with the SA-codes, and, (g) the statistical evaluation of the results using the capabilities, i.e. methods and tools offered by the UQ-tools. This paper describes the project status of the UQ of different SA codes for the selected SA sequences, and the technical challenges and lessons learnt from the preparatory and exploratory investigations performed.

論文

A First glimpse at the shell structure beyond $$^{54}$$Ca; Spectroscopy of $$^{55}$$K, $$^{55}$$Ca, and $$^{57}$$Ca

小岩井 拓真*; Wimmer, K.*; Doornenbal, P.*; Obertelli, A.*; Barbieri, C.*; Duguet, T.*; Holt, J. D.*; 宮城 宇志*; Navr$'a$til, P.*; 緒方 一介*; et al.

Physics Letters B, 827, p.136953_1 - 136953_7, 2022/04

https://doi.org/10.1016/j.physletb.2022.136953
 被引用回数：2 パーセンタイル：79.5(Astronomy & Astrophysics)

中性子過剰核$$^{54}$$Caでは、新魔法数34が発見されて以来、その構造を知るために多くの実験がなされてきたが、それを超える中性子過剰核の情報は全く知られてこなかった。本論文では、理化学研究所RIBFにて$$^{55}$$K, $$^{55}$$Ca, $$^{57}$$Caの励起状態から脱励起するガンマ線を初めて観測した結果を報告した。それぞれ1つのガンマ線しか得られなかったものの、$$^{55}$$Kおよび$$^{55}$$Caのデータは、それぞれ、陽子の$$d_{3/2}$$と$$s_{1/2}$$軌道間のエネルギー差、中性子の$$p_{1/2}$$と$$f_{5/2}$$軌道間のエネルギー差を敏感に反映し、両方とも最新の殻模型計算によって200keV程度の精度で再現できることがわかった。また、1粒子状態の程度を特徴づける分光学的因子を実験データと歪曲波インパルス近似による反応計算から求め、その値も殻模型計算の値と矛盾しないことがわかった。

論文

Japanese pediatric and adult atomic bomb survivor dosimetry; Potential improvements using the J45 phantom series and modern Monte Carlo transport

Griffin, K. T.*; 佐藤 達彦; 船本 幸代*; Chizhov, K.*; Domal, S.*; Paulbeck, C.*; Bolch, W.*; Cullings, H. M.*; Egbert, S. D.*; 遠藤 章; et al.

Radiation and Environmental Biophysics, 61(1), p.73 - 86, 2022/03

https://doi.org/10.1007/s00411-021-00946-2
 被引用回数：2 パーセンタイル：41.94(Biology)

原爆生存者に対する線量評価は、放射線被ばくリスクを評価する上で極めて重要となる。原子力機構,放射線影響研究所,フロリダ大学,米国がんセンターらで構成する研究チームは、これまで、1945年の日本人体型を反映した成人,小児及び胎児を含む妊婦の人体模型を作成し、前方照射や等方照射など理想的な照射条件に対してその臓器線量を評価してきた。本研究では、原爆線量評価システムDS02に含まれる現実的な20照射条件に対して、成人及び小児の臓器線量を詳細に評価した。その結果、全線量は、造血組織,結腸,胃壁に関しては、従来手法(DS92)と比較してそれぞれ20%, 20%、及び15%の違いがあることが分かった。また中性子線量だけに着目すると、最大で2倍程度の差があることが分かった。

論文

In-situ neutron diffraction study of lattice deformation behaviour of commercially pure titanium at cryogenic temperature

Lee, M.-S.*; 川崎 卓郎; 山下 享介*; Harjo S.; Hyun, Y.-T.*; Jeong, Y.*; Jun, T.-S.*

Scientific Reports (Internet), 12(1), p.3719_1 - 3719_10, 2022/03

https://doi.org/10.1038/s41598-022-07640-3
 被引用回数：1 パーセンタイル：46.38(Multidisciplinary Sciences)

Titanium has a significant potential for the cryogenic industrial fields such as aerospace and liquefied gas storage and transportation due to its excellent low temperature properties. To develop and advance the technologies in cryogenic industries, it is required to fully understand the underlying deformation mechanisms of Ti under the extreme cryogenic environment. Here, we report a study of the lattice behaviour in grain families of Grade 2 CP-Ti during in-situ neutron diffraction test in tension at temperatures of 15-298 K. Combined with the neutron diffraction intensity analysis, EBSD measurements revealed that the twinning activity was more active at lower temperature, and the behaviour was complicated with decreasing temperature.

論文

Grain-size-dependent microstructure effects on cyclic deformation mechanisms in CoCrFeMnNi high-entropy-alloys

Luo, M.-Y.*; Lam, T.-N.*; Wang, P.-T.*; Tsou, N.-T.*; Chang, Y.-J.*; Feng, R.*; 川崎 卓郎; Harjo S.; Liaw, P. K.*; Yeh, A.-C.*; et al.

Scripta Materialia, 210, p.114459_1 - 114459_7, 2022/03

https://doi.org/10.1016/j.scriptamat.2021.114459
 被引用回数：5 パーセンタイル：91.36(Nanoscience & Nanotechnology)

The effect of grain size on strain-controlled low-cycle fatigue (LCF) properties in the CoCrFeMnNi high-entropy alloys (HEAs) was investigated towards the distinct microstructural developments during cyclic loading at a strain amplitude of $$pm$$ 1.0%. A much more prominent secondary cyclic hardening (SCH) behavior at the final deformation stage was observed in the fine-grained (FG) than in the coarse-grained (CG) CoCrFeMnNi. In-situ neutron-diffraction and microscopic examination, strongly corroborated by molecular dynamic (MD) simulations, indicated that dislocation activities from planar slip to wavy slip-driven subgrain structures within the grains acted as the primary cyclic-deformation behaviors in the FG CoCrFeMnNi. Differently observed in the cyclic behavior of the CG CoCrFeMnNi was due to a transition from the planar dislocation slip to twinning.

論文

Tensile response of as-cast CoCrFeNi and CoCrFeMnNi high-entropy alloys

Lam, T.-N.*; Luo, M.-Y.*; 川崎 卓郎; Harjo S.; Jain, J.*; Lee, S.-Y.*; Yeh, A.-C.*; Huang, E.-W.*

Crystals (Internet), 12(2), p.157_1 - 157_9, 2022/02

https://doi.org/10.3390/cryst12020157
 被引用回数：2 パーセンタイル：80.78(Crystallography)

In this research, we systematically investigated equiatomic CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs). Both of these HEA systems are single-phase, face-centered-cubic (FCC) structures. Specifically, we examined the tensile response in as-cast quaternary CoCrFeNi and quinary CoCrFeMnNi HEAs at room temperature. Compared to CoCrFeNi HEA, the elongation of CoCrFeMnNi HEA was 14% lower, but the yield strength and ultimate tensile strength were increased by 17% and 6%, respectively. The direct real-time evolution of structural defects during uniaxial straining was acquired via in situ neutron-diffraction measurements. The dominant microstructures underlying plastic deformation mechanisms at each deformation stage in as-cast CoCrFeNi and CoCrFeMnNi HEAs were revealed using the Convolutional Multiple Whole Profile (CMWP) software for peak-profile fitting. The possible mechanisms are reported.

論文

Microstructural evolution and mechanical properties of non-equiatomic (CoNi)$$_{74.66}$$Cr$$_{17}$$Fe$$_{8}$$C$$_{0.34}$$ high-entropy alloy

Kim, Y. S.*; Chae, H.*; Huang, E.-W.*; Jain, J.*; Harjo S.; 川崎 卓郎; Hong, S. I.*; Lee, S. Y.*

Materials, 15(4), p.1312_1 - 1312_11, 2022/02

https://doi.org/10.3390/ma15041312
 被引用回数：0 パーセンタイル：0(Chemistry, Physical)

In this study, we manufactured a non-equiatomic (CoNi)$$_{74.66}$$Cr$$_{17}$$Fe$$_{8}$$C$$_{0.34}$$ high-entropy alloy (HEA) consisting of a single-phase face-centered-cubic structure. The non-equiatomic (CoNi)$$_{74.66}$$Cr$$_{17}$$Fe$$_{8}$$C$$_{0.34}$$ HEA revealed a good combination of strength and ductility in mechanical properties compared to the equiatomic CoNiCrFe HEA, due to both stable solid solution and precipitation-strengthened effects. The non-equiatomic stoichiometry resulted in not only a lower electronegativity mismatch, indicating a more stable state of solid solution, but also a higher stacking fault energy (SFE, $$sim$$50 mJ/m$$^{2}$$) due to the higher amount of Ni and the lower amount of Cr. This higher SFE led to a more active motion of dislocations relative to mechanical twinning, resulting in severe lattice distortion near the grain boundaries and dislocation entanglement near the twin boundaries.

論文

Multiple deformation scheme in direct energy deposited CoCrNi medium entropy alloy at 210K

Kim, Y. S.*; Chae, H.*; Woo, W.*; Kim, D.-K.*; Lee, D.-H.*; Harjo S.; 川崎 卓郎; Lee, S. Y.*

Materials Science & Engineering A, 828, p.142059_1 - 142059_10, 2021/11

https://doi.org/10.1016/j.msea.2021.142059
 被引用回数：3 パーセンタイル：42.06(Nanoscience & Nanotechnology)

CoCrNi medium entropy alloy (MEA) and stainless steel 316L (SS316L) were manufactured by direct energy deposition of additive manufacturing (DED-AM). Exceptional mechanical properties of DED CoCrNi at 210K were achieved by the activities of a multiple deformation scheme that changed from dislocation slip to twinning-induced plasticity followed by transformation-induced plasticity. While SS316L at room temperature has micro-twins, CoCrNi at 210K exhibited nano-twins, resulting from lower stacking fault energy. Moreover, transformed hexagonal close-packed (HCP) phases were found near the face-centered cubic (FCC) {111} grain boundaries, where remarkable stacking faults and severe lattice distortion were measured.

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