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

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.

Pairing forces govern population of doubly magic Ca from direct reactions

Browne, F.*; Chen, S.*; Doornenbal, P.*; Obertelli, A.*; 緒方 一介*; 宇都野 穣; 吉田 数貴; Achouri, N. L.*; 馬場 秀忠*; Calvet, D.*; et al.

Physical Review Letters, 126(25), p.252501_1 - 252501_7, 2021/06

https://doi.org/10.1103/PhysRevLett.126.252501

理化学研究所RIビームファクトリーにて、中性子過剰核Scからの1陽子ノックアウト反応によってCaを生成し、そのエネルギー準位と反応断面積をガンマ線分光および不変質量分光によって得た。その結果を歪曲波インパルス近似による核反応計算と大規模殻模型による核構造計算を組み合わせた理論値と比較した。実験の準位と断面積は理論計算によってよく再現された。Caの正パリティ状態については、基底状態の生成断面積が励起状態のものに比べて圧倒的に大きいという結果が得られた。これは、Scでは中性子魔法数34が消滅しCaではその魔法数が存在するというこれまでの知見と一見矛盾するが、対相関による分光学的因子のコヒーレンスから理解することができる。

Effect of the difference in strength of hard and soft components on the synergetic strengthening of layered materials

Kim, J. G.*; Bae, J. W.*; Park, J. M.*; Woo, W.*; Harjo, S.; Lee, S.*; Kim, H. S.*

Metals and Materials International, 27(2), p.376 - 383, 2021/02

https://doi.org/10.1007/s12540-020-00657-1

Heterogeneous structured materials achieve a combination of high strength and extreme ductility due to synergetic strengthening driven by conditions in the interfacial region. Although the origin of synergetic strengthening has been revealed to be strain incompatibility in the interfacial region, the effect of the strength difference between hard and soft phases on strengthening has not been investigated well. In the work reported in the present paper, the effect of the difference in strength of the hard and soft phases on synergetic strengthening was investigated by conducting in situ neutron diffraction tensile tests. As a result, it was determined that the dislocation density in a layered sheet of high Mn (HMn) steel/interstitial free (IF) steel is higher than that in a layered sheet of HMn/low carbon steel. The big difference in mechanical properties between HMn steel and IF steel induces a high stress gradient and results in additional dislocations.

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

https://doi.org/10.1016/j.actamat.2020.10.016

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.

DECOVALEX-2019 Task D; INBEB Final Report

Gens, A.*; Alcoverro, J.*; Blaheta, R.*; Hasal, M.*; Michalec, Z.*; 高山 裕介; Lee, C.*; Lee, J.*; Kim, G. Y.*; Kuo, C.-W.*; et al.

LBNL-2001267 (Internet), 210 Pages, 2020/10

放射性廃棄物を地層処分した際に、廃棄体やその周囲で起こる熱-水理-力学-化学が連成する現象を表現する連成モデルの開発と確証を目的に、国際共同研究「DECOVALEX 2019 (DEvelopment of COupled models and their VALidation against EXperiments 2019)」が2016年4月から2019年12月までの期間で実施された。DECOVALEX-2019のタスクDは、スイスのモン・テリ岩盤研究所およびグリムゼル試験サイトで実施されている原位置試験(それぞれ、EB試験およびFEBEX試験)を対象とした解析課題であり、廃棄体定置後のベントナイト材料からなる緩衝材等の人工バリア及び岩盤を対象に緩衝材が不飽和から飽和に至る状態までの熱-水理-力学連成現象のモデル化に関する検討が行われた。タスクDの参加チームは、IGN(チェコ), KAERI(韓国), NCU/TP(台湾), JAEA(日本)の4チームである。本報告書は、DECOVALEX-2019プロジェクトのタスクDの最終レポートであり、得られた成果や課題等について取りまとめたものである。

The Joint evaluated fission and fusion nuclear data library, JEFF-3.3

Plompen, A. J. M.*; Cabellos, O.*; De Saint Jean, C.*; Fleming, M.*; Algora, A.*; Angelone, M.*; Archier, P.*; Bauge, E.*; Bersillon, O.*; Blokhin, A.*; et al.

European Physical Journal A, 56(7), p.181_1 - 181_108, 2020/07

https://doi.org/10.1140/epja/s10050-020-00141-9

本論文では、核分裂と核融合のための統合評価済み核データファイルのバージョン3.3(JEFF-3.3)について説明する。中性子との反応が重要な核種のU, U, Pu, Am, Na, Ni, Cr, Cu, Zr, Cd, Hf, Au, Pb, Biについて、新しい核データ評価結果を示す。JEFF-3.3には、核分裂収率, 即発核分裂スペクトル, 核分裂平均中性子発生数の新しいデータが含まれる。更に、放射崩壊, 熱中性子散乱, ガンマ線放出, 中性子による放射化, 遅発中性子, 照射損傷に関する新しいデータも含まれている。JEFF-3.3は、TENDLプロジェクトのファイルで補完しており、光子, 陽子, 重陽子, 三重陽子, He核, アルファ粒子による反応ライブラリについては、TENDL-2017から採用した。また、不確かさの定量化に対する要求の高まりから、多くの共分散データが新しく追加された。JEFF-3.3を用いた解析の結果と臨界性, 遅発中性子割合, 遮蔽, 崩壊熱に対するベンチマーク実験の結果を比較することにより、JEFF-3.3は幅広い原子核技術の応用分野、特に原子力エネルギーの分野において優れた性能を持っていることが分かった。

Comparison of dislocation density, twin fault probability, and stacking fault energy between CrCoNi and CrCoNiFe medium entropy alloys deformed at 293 and 140K

Woo, W.*; Naeem, M.*; Jeong, J.-S.*; Lee, C.-M.*; Harjo, S.; 川崎 卓郎; He, H.*; Wang, X.-L.*

Materials Science & Engineering A, 781, p.139224_1 - 139224_7, 2020/04

https://doi.org/10.1016/j.msea.2020.139224

To elucidate deformation behavior behind the exceptional mechanical properties of CrCoNi based medium entropy alloys, the deformation related microstructural parameters were determined by using in situ neutron diffraction and peaks profile analysis methods. Superior tensile strength and elongation of the CrCoNi alloy is relevant to higher twin fault probability (, up to 3.8%) and dislocation density (, up to 9.7 10 m) compared to those (1.3% and 3.4 10 m, respectively) of the CrCoNiFe at 293K. Meanwhile, at 140K, the of the CrCoNiFe significantly increased up to 4.4% with the stable of 5.0 10 m and its mechanical properties overwhelm those of the CrCoNi at 273K. Such twinning dominant deformation mechanism at low temperature is also assured by lower stacking fault energy (SFE) of the CrCoNiFe at 140K compared to those of the CrCoNi and CrCoNiFe alloys at 293K.

Stacking fault energy analyses of additively manufactured stainless steel 316L and CrCoNi medium entropy alloy using in situ neutron diffraction

Woo, W.*; Jeong, J.-S.*; Kim, D.-K.*; Lee, C. M.*; Choi, S.-H.*; Suh, J.-Y.*; Lee, S. Y.*; Harjo, S.; 川崎 卓郎

Scientific Reports (Internet), 10(1), p.1350_1 - 1350_15, 2020/01

https://doi.org/10.1038/s41598-020-58273-3

Stacking fault energies (SFE) were determined in additively manufactured (AM) stainless steel (SS 316 L) and equiatomic CrCoNi medium-entropy alloys. In situ neutron diffraction was performed to obtain a number of faulting-embedded diffraction peaks simultaneously from a set of (hkl) grains during deformation. The peak profiles diffracted from imperfect crystal structures were analyzed to correlate stacking fault probabilities and mean-square lattice strains to the SFE. The result shows that averaged SFEs are 32.8 mJ/m for the AM SS 316 L and 15.1 mJ/m for the AM CrCoNi alloys. Meanwhile, during deformation, the SFE varies from 46 to 21 mJ/m (AM SS 316 L) and 24 to 11 mJ/m (AM CrCoNi) from initial to stabilized stages, respectively. The transient SFEs are attributed to the deformation activity changes from dislocation slip to twinning as straining.

Comparing cyclic tension-compression effects on CoCrFeMnNi high-entropy alloy and Ni-based superalloy

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

AA2019-0503.pdf:1.06MB

https://doi.org/10.3390/cryst9080420

An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both metallic systems. However, as obtained from the diffraction-peak-width evolution, the underneath deformation mechanisms are quite different. The CoCrFeMnNi HEA exhibits distinct lattice strain and microstructure responses under tension-compression cyclic loadings.

Dosimetric impact of a new computational voxel phantom series for the Japanese atomic bomb survivors; Pregnant females

Paulbeck, C.*; Griffin, K.*; Lee, C.*; Cullings, H.*; Egbert, S. D.*; 船本 幸代*; 佐藤 達彦; 遠藤 章; Hertel, N.*; Bolch, W. E.*

Radiation Research, 192(5), p.538 - 561, 2019/08

https://doi.org/10.1667/RR15394.1

妊婦及び胎児の原爆生存者に対する被ばく線量評価は、放射線影響の疫学研究の上で極めて重要となる。従来は、女性の子宮壁に対する線量を妊婦及び胎児の被ばく線量と仮定していたが、本研究では、最新の計算科学記述を用いて受胎8, 15, 25, 38週齢の胎児及び妊婦に対する詳細人体モデルを構築し、その被ばく線量を精度よく計算した。その結果、従来手法では、光子及び中性子前方照射に対して最大で12-16%及び44-54%被ばく線量を過大評価していたことが分かった。これらの結果は、今後、妊婦及び胎児に対する放射線感受性の疫学調査を実施する上で、極めて重要となる。