Evaluation of residual stress distribution in linear friction welded steel joint neutron diffraction mapping measurement

山下 享介*; 柳樂 知也*; Gong, W.; 川崎 卓郎; Harjo, S.; 潮田 浩作*; 藤井 英俊*

ISIJ International, 66(5), p.673 - 684, 2026/04

https://doi.org/10.2355/isijinternational.ISIJINT-2025-405

In this study, neutron diffraction mapping was performed on linear friction welded (LFW) joints of 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate residual stress, dislocation density, and crystallographic orientation. Welding was conducted under applied pressures of 100 and 250 MPa. The weld interface mainly consisted of refined ferrite with minor retained austenite and martensite, indicating reverse transformation to austenite during welding. The 250 MPa condition resulted in a lower welding temperature. Elongated grains were observed near the surface along the oscillation direction, while equiaxed grains appeared at the center. Both joints showed high tensile residual stresses at the weld center and compressive stresses near the surface. Higher applied pressure increased dislocation density because of suppressed dynamic recovery. Strong texture formation due to plastic flow was observed, while the effect of applied pressure on texture development was limited.

令和6年度緊急時対応技術適用のためのバックグラウンド航空機モニタリング及び無人航空機による放射線モニタリングに係る技術開発(受託研究)

普天間 章; 越智 康太郎; 佐々木 美雪; 中間 茂雄; 川崎 義晴*; 岩井 毅行*; 平賀 祥吾*; 萩野谷 仁*; 松永 祐樹*; 眞田 幸尚; et al.

JAEA-Technology 2025-015, 171 Pages, 2026/03

JAEA-Technology-2025-015.pdf:11.43MB

2011年(平成23年)3月11日に発生した東北地方太平洋沖地震に伴う津波により、東京電力福島第一原子力発電所事故が発生し、大量の放射性物質が周辺環境に飛散した。事故直後から、放射線の分布を迅速かつ広範囲に測定する手段として、有人ヘリコプター等による航空機モニタリングが活用されてきた。日本原子力研究開発機構は原子力規制庁からの受託事業として、緊急時モニタリングの迅速化に向け、発電所周辺のバックグラウンド線量率や地形、管制空域等の情報整備を進めている。令和6年度は、島根原子力発電所周辺で航空機モニタリングを実施し、線量率マップ等を作成し、地上測定値や他機関データと比較して妥当性を確認した。原子力総合防災訓練では、有人ヘリコプターに加え無人航空機を用いた訓練フライトを実施し、搭載方法やリアルタイム通信、迅速なマッピングの有効性を確認した。さらに、無人機データ収集システムの整備を進め、リアルタイム解析やマルチプラットフォームでの運用を検証し、改良課題を抽出した。マルチコプターの操作講習も実施し、運用技術の向上を図った。加えて、米国、フランス、韓国、カナダと合同環境放射線モニタリングを行い、各国の測定技術や運用体制に関する知見を得るとともに、国際的な情報共有の重要性を確認した。本報告書は、これら令和6年度の受託研究で得られた成果と技術的課題を取りまとめ、今後の緊急時モニタリング技術の高度化に資する知見を提供するものである。

Stress and temperature, rather than hydrogen, govern stacking fault evolution during tensile deformation in Fe-24Cr-19Ni steel

伊東 達矢; 小川 祐平*; Gong, W.; 川崎 卓郎; 柴田 曉伸*; Harjo, S.

Scripta Materialia, 273, p.117084_1 - 117084_6, 2026/03

https://doi.org/10.1016/j.scriptamat.2025.117084

The effect of solute hydrogen on stacking fault evolution in austenitic steels remains debated. In this study, the changes in stacking fault probability in the 111//loading direction grains family () of hydrogen-charged and non-charged Fe-24Cr-19Ni austenitic steels were evaluated using neutron diffraction during tensile deformation at 223 and 177 K. When values were plotted against macroscopic strain, hydrogen apparently enhanced stacking fault evolution. However, when identical data were translated into the form of versus stress, the superficial hydrogen-effect on notably disappeared. Rather, deformation temperature played more predominant role - lower temperature led to higher regardless of hydrogen-charging, reflecting the reduction of stacking fault energy with decreasing temperature. These findings demonstrate that hydrogen has a minor effect on stacking fault evolution compared with temperature and applied stress.

Effect of nanoscale cellular structure on the mechanical properties of Inconel 718 with unique hierarchical structure fabricated by laser powder bed fusion

Cho, K.*; 山下 葵平*; 角谷 心之輔*; 齊藤 拓馬*; 佐々木 泰祐*; 澤泉 克彦*; 奥川 将行*; 小泉 雄一郎*; 眞山 剛*; 菊川 泰地*; et al.

Acta Materialia, 303, p.121696_1 - 121696_18, 2026/01

https://doi.org/10.1016/j.actamat.2025.121696

The deformation behavior and strengthening mechanism of Inconel 718 with a hierarchical structure composed of microscale crystallographic lamellar microstructure (CLM) and nanoscale cellular structure, fabricated by laser powder bed fusion, were clarified via nanoscale microstructural and in-situ neutron diffraction analyses. The CLM is a layered structure parallel to the building direction (BD) and consists of relatively wide main and narrow sub-layers with 110 and 100 orientations, respectively, with respect to BD. This is the first study to demonstrate that the yield stress of the alloys depends strongly on deformation stresses of the sub-layers, even though Schmid factors of the primary slip system for both layers are the same. The sub-layer continues to deform elastically even beyond the micro-yield point of the main layer, which results in the macroscopic strengthening at an early stage of deformation. On the other hand, the cellular structure is formed in both layers, associated with a dendritic cell growth along 100 direction, Nb segregation between the cells and an accumulation of dislocations to decrease a residual stress. The cell boundaries with numerous dislocations and Nb segregation act as a strong barrier to dislocation motion resulting in a stress increase through the Hall-Petch law, even though they are low-angle grain boundaries. The spacing and morphology of the cell boundary depend strongly on fabrication conditions. The optimized cellular structure provides significant strengthening comparable to or greater than that caused by large-angle grain boundaries, thereby increasing the macroscopic strength of the alloys through hardening of the sub-layer.

中性子回折マッピング測定法を用いた線形摩擦接合鋼継手の残留応力分布評価

山下 享介*; 柳樂 知也*; Gong, W.; 川崎 卓郎; Harjo, S.; 潮田 浩作*; 藤井 英俊*

鉄と鋼, 111(17), p.1057 - 1071, 2025/12

https://doi.org/10.2355/tetsutohagane.TETSU-2025-042

Neutron diffraction mapping was conducted on linear friction welded joints of 12 mm thick high-phosphorus weathering steel (SPA-H) to evaluate residual stress, dislocation density, and crystallographic orientation. Welding was performed at 100 MPa and 250 MPa. The weld interface mainly comprised refined ferrite with retained austenite and martensite, indicating temperatures exceeded A1 and induced reverse transformation. The 250 MPa joint showed a lower welding temperature. Elongated grains formed near the surface along the oscillation direction (OD), while equiaxed grains appeared at the center. High tensile residual stresses were found at the weld center, with compressive stress near the surface perpendicular to the weld. Pressure had little effect on overall stress trends. Dislocation density increased with pressure due to suppressed dynamic recovery. Strong texture developed at the interface, with limited pressure dependence.

ロシアの核エネルギー民生利用方法に関する分析研究

川崎 信史

JAEA-Review 2025-043, 74 Pages, 2025/10

JAEA-Review-2025-043.pdf:2.45MB

ロシアは、民生分野における核エネルギー利用において、世界の最先端を行く先進国であるが、その内情の把握は、種々の理由により難しいものとなっている。そこで、ロシアの核エネルギー利用、核燃料供給、燃料製造能力、再処理・燃料サイクルの考え方について、その意図と成果に関する歴史的な整理を行い、そこから得られる知見を抽出した。また、本知見から見えてくる戦略を、「開発・実証の戦略的多様性と連続性」及び「技術活用・展開方法の多様性」として整理し、日本にとっての示唆も含めて以下のように考察した。ロシアの核エネルギー政策は、多様な原子炉型式と燃料サイクル技術を戦略的に活用し、国内外での原子力発電の拡大を目指すものである。現在、軽水炉(VVERシリーズ)を中心に、原子力発電は国内の電力発電量の約20%を占めており、2045年までにこれを25%に引き上げる計画が進められている。ロシアでは、大型炉から中型・小型モジュール炉まで、さまざまなタイプの原子炉の建設が進められており、高速炉技術の開発や、使用済み燃料の再処理・リサイクルにも注力している。国際的には、VVER-1200などの原子炉を複数の国で建設中であり、高速炉分野では中国との協力も深まっている。特筆すべき点は、ロシアが原子炉の導入から燃料の供給、再処理、廃棄物管理、さらには放射性同位体(RI)の提供に至るまで、これらすべてを一体的、あるいは部分的に選択可能な技術サービスとして、国際的に提供している点である。単なる製品の輸出や技術の供与にとどまらず、相手国の状況やニーズに応じた柔軟な対応を通じて、持続的な関係の構築と信頼の醸成を図っている。このような国際展開を可能にするために、ロシア国内では将来的に海外での展開が見込まれる分野において先行的に技術開発を進め、対象となる技術やサービスを選定し、計画的に展開を図っている。このような「技術の多様性」と「戦略の一体性」を兼ね備えた柔軟な展開は、さまざまな地政学的背景を持つ国々との協力を可能にしており、日本にとっても、単に技術を輸出するのではなく、燃料サイクル全体を見据えた包括的な国際協力のあり方や、高速炉やRI供給などを組み合わせた多角的なアプローチとして参考になる。

Microscopic insights into the mechanical behavior of a Ni-Co-based superalloy through neutron diffraction

Liu, Y.*; Yan, Z.*; Gao, Y.*; Li, Y.*; Gan, B.*; Harjo, S.; Gong, W.; 川崎 卓郎; Li, S.*; Wang, Y.-D.*

Microstructures (Internet), 5(4), p.2025096_1 - 2025096_15, 2025/10

https://doi.org/10.20517/microstructures.2025.28

The micromechanical behaviors and dislocation evolution in a polycrystalline Ni-Co-based superalloy were systematically investigated by neutron diffraction tensile testing combined with line profile analysis. The results reveal the sequential activation of ' shearing and Orowan looping mechanisms, with interphase load partitioning governed by strain-dependent interactions of dislocation and precipitate. During the initial plastic deformation, the and ' phases undergo co-deformation through dislocation shearing without load transfer, while the Orowan looping facilitates the load transfer from to ' phase at a higher strain level. Furthermore, the low stacking fault energy leads to a rising fraction of screw dislocations by suppressing cross-slip. Crucially, the pinning effect of ' precipitates hinders the rearrangement of these dislocations into low-energy structures, resulting in the formation of high-energy, weakly screened dislocation configurations. These findings provide new evidence for the planar slip dominance in Ni-Co-based superalloys, enabling quantitative assessment of microstructural evolution and micromechanical responses.

Enhanced work hardening in ferrite and austenite of duplex stainless steel at 200 K; neutron diffraction study

山下 享介*; 古賀 紀光*; Mao, W.*; Gong, W.; 川崎 卓郎; Harjo, S.; 藤井 英俊*; 梅澤 修*

Materials Science & Engineering A, 941, p.148602_1 - 148602_11, 2025/09

https://doi.org/10.1016/j.msea.2025.148602

Ferrite-austenite duplex stainless steels offer excellent strength and ductility, making them suitable for extreme environments. In this study, neutron diffraction during tensile testing at 293 K and 200 K was used to investigate stress partitioning and phase-specific deformation. Phase stress was calculated using a texture-compensated method. At both temperatures, ferrite showed higher phase stress than austenite, acting as the harder phase. At 200 K, both phases exhibited increased strength and work hardening. Austenite showed significant stacking fault formation alongside dislocation migration, while ferrite retained its dislocation-based deformation mode, becoming more effective. Stress contributions from both phases were comparable. No martensitic transformation occurred. Strengthening and enhanced work hardening in both phases led to high strength at 200 K, with ductility similar to that at 293 K.

その場中性子回折を用いたSUS310Sステンレス鋼の水素添加による強さ・伸び向上メカニズムの解明

伊東 達矢; 小川 祐平*; Gong, W.; Mao, W.*; 川崎 卓郎; 岡田 和歩*; 柴田 曉伸*; Harjo, S.

波紋, 35(3), p.129 - 133, 2025/08

Recent studies have shown that the addition of hydrogen to SUS310S stainless steel (Fe-24Cr-19Ni, mass%) simultaneously enhances both strength and ductility, indicating a phenomenon contrary to the conventional understanding of hydrogen embrittlement. In this study, we investigated the underlying mechanism through neutron diffraction experiments during tensile deformation using TAKUMI at the MLF of J-PARC. The results revealed that solid-solution strengthening by hydrogen plays the most significant role in improving the mechanical properties. Solute hydrogen atoms distort the lattice to suppress dislocation motion, thereby increasing the strength. The raised stress in the hydrogen charged sample enables the onset of deformation twinning at a smaller strain compared to the non-hydrogen charged sample. Consequently, the twinning-induced plasticity effect contributes more significantly to work hardening and the improvement of uniform elongation due to the solid-solution strengthening by hydrogen. These findings suggest a new pathway for the effective utilization of hydrogen in austenitic steels.

Enhancing the strength and ductility of a medium entropy alloy through non-basal slip activation

Chen, Z.*; Gong, W.; Harjo, S.; 川崎 卓郎; Chen, G.*; 他14名*

Nature Communications (Internet), 16, p.6480_1 - 6480_13, 2025/07

https://doi.org/10.1038/s41467-025-61494-7

Developing alloys with both ultrahigh strength and ductility remains a for- midable scientific challenge, primarily due to the inherent strength-ductility tradeoff. Here, we present an approach to enhance the ductility and strength of a medium-entropy alloy (MEA) featuring a fully recrystallized face-centered cubic/hexagonal close-packed dual-phase ultrafine-grained architecture. This is achieved by activating unusual non-basal slips in the ordered hexagonal close-packed superlattice nanoprecipitates, resulting in this MEA that exhibits remarkable uniform elongation () and ultrahigh yield strength () across a wide temperature range, particularly at cryogenic temperatures ( 2100 MPa, 15%). The non-basal slips in the secondary phase are activated at ultrahigh stress levels, which are compatible with the increased yield strength of the MEA attained through multiple strengthening mechanisms, including grain boundaries, lattice friction, and second-phase nanoprecipitates provided by the multi-principal elements of the entropy alloy. The deformation mechanism elucidated in this work not only leverages the significant strengthening and strain hardening effects of brittle nanoprecipitates but also enables the ductilization of the alloy through sequential non-basal slip during ongoing deformation.