Quantitative analysis of microstructure evolution, stress partitioning and thermodynamics in the dynamic transformation of Fe-14Ni alloy

Li, L.*; 宮本 吾郎*; Zhang, Y.*; Li, M.*; 諸岡 聡; 及川 勝成*; 友田 陽*; 古原 忠*

Journal of Materials Science & Technology, 184, p.221 - 234, 2024/06

https://doi.org/10.1016/j.jmst.2023.10.037

Dynamic transformation (DT) of austenite () to ferrite () in the hot deformation of various carbon steels was widely investigated. However, the nature of DT remains unclear due to the lack of quantitative analysis of stress partitioning between two phases and the uncertainty of local distribution of substitutional elements at the interface in multi-component carbon steels used in the previous studies. Therefore, in the present study, a binary Fe-Ni alloy with + duplex microstructure in equilibrium was prepared and isothermally compressed in + two-phase region to achieve quantitative analysis of microstructure evolution, stress partitioning and thermodynamics during DT. to DT during isothermal compression and to reverse transformation on isothermal annealing under unloaded condition after deformation were accompanied by Ni partitioning. The lattice strains during thermomechanical processing were obtained via in-situ neutron diffraction measurement, based on which the stress partitioning behavior between and was discussed by using the generalized Hooke's law. A thermodynamic framework for the isothermal deformation in solids was established based on the basic laws of thermodynamics, and it was shown that the total Helmholtz free energy change in the deformable material during the isothermal process should be smaller than the work done to the deformable material. Under the present thermodynamic framework, the microstructure evolution in the isothermal compression of Fe-14Ni alloy was well explained by considering the changes in chemical free energy, plastic and elastic energies and the work done to the material. In addition, the stabilization of the soft phase in Fe-14Ni alloy by deformation was rationalized since the to transformation decreased the total Helmholtz free energy by decreasing the elastic and dislocation energies.

「2021年度環境報告書」環境報告関連データのまとめ

安全管理部 施設保安管理課

JAEA-Review 2023-035, 218 Pages, 2024/03

JAEA-Review-2023-035.pdf:8.47MB

日本原子力研究開発機構(以下「原子力機構」という。)は、2021年度の環境配慮活動について、「環境情報の提供の促進等による特定事業者等の環境に配慮した事業活動の促進に関する法律」に基づき「2021年度環境報告書」を作成し、2022年9月に原子力機構のホームページで公表した。本報告書は、環境報告の信頼性を高めるためにその情報の検証可能性を確保し、また、原子力機構における環境配慮活動の取組を推進する手段として、環境報告書に記載した環境関連情報の根拠となる2021年度の環境報告関連データ及び他のさまざまな環境配慮活動の関連情報を取りまとめたものである。

廃棄体製作基準類整備に関する活動; 令和4年度活動報告書

バックエンド推進部; 埋設事業センター

JAEA-Review 2023-037, 162 Pages, 2024/02

JAEA-Review-2023-037.pdf:2.66MB

日本原子力研究開発機構では、研究施設等廃棄物の浅地中処分に向けて、廃棄物確認における技術基準への対応方法等の検討を進めている。令和4年度から「廃棄体製作基準検討委員会」を設置し、埋設事業センターにて検討中の廃棄物埋設施設を想定した暫定の廃棄物受入基準、廃棄体確認要領等の廃棄体製作に関する基準類の整備を進めていくこととした。令和4年度は、液体廃棄物のセメント固化体及び固体廃棄物の充填固化体に関する基準類を策定することとし、検討を進めた。また、廃棄物確認の方法が確立されていない課題の検討、解体廃棄物の合理的な処理方法の実証等を進めた。本報告書は、それらの内容についてまとめたものである。

Fe-5Mn-0.1C中Mn鋼におけるリューダース変形中の微視組織および塑性の発達

小山 元道*; 山下 享介*; 諸岡 聡; 澤口 孝宏*; Yang, Z.*; 北條 智彦*; 川崎 卓郎; Harjo, S.

鉄と鋼, 110(3), p.197 - 204, 2024/02

https://doi.org/10.2355/tetsutohagane.TETSU-2023-038

The local plasticity and associated microstructure evolution in Fe-5Mn-0.1C medium-Mn steel (wt.%) were investigated in this study. Specifically, the micro-deformation mechanism during Lders banding was characterized based on multi-scale electron backscatter diffraction measurements and electron channeling contrast imaging. Similar to other medium-Mn steels, the Fe-5Mn-0.1C steel showed discontinuous macroscopic deformation, preferential plastic deformation in austenite, and deformation-induced martensitic transformation during Lders deformation. Hexagonal close-packed martensite was also observed as an intermediate phase. Furthermore, an in-situ neutron diffraction experiment revealed that the pre-existing body- centered cubic phase, which was mainly ferrite, was a minor deformation path, although ferrite was the major constituent phase.

残留オーステナイトを含有する中Mn複合組織鋼の高速変形特性

興津 貴隆*; 北條 智彦*; 諸岡 聡; 宮本 吾郎*

鉄と鋼, 110(3), p.260 - 267, 2024/02

https://doi.org/10.2355/tetsutohagane.TETSU-2023-065

We have investigated the dynamic tensile properties of 4, 5, 6-mass%-Mn-containing low carbon steels with multi-phase microstructures containing retained austenite. The five materials used were classified into two groups. The first group of materials, with around 10% of retained austenite, showed normal strain rete dependence of yield strength (YS) and tensile strength (TS) as in conventional high strength steels. The second group of materials, containing 25-36% of retained austenite, exhibited Lders elongation showed also normal strain rate dependence in YS and flow stress at Lders deformation, but TS varied in a complex manner. Among the second group, in the 4 Mn steel, TS was nearly constant at strain rates below 1 s but increased slightly at higher strain rates. In the 5 and 6 Mn steels, TS once decreased up to the strain rate of 1 or 10 s, and then began to increase at higher strain rates. These behaviors were discussed in terms of temperature rise during plastic deformation causing suppression of martensitic transformation, and thermal stability of retained austenite. In the 4 Mn steel with relatively unstable retained austenite, almost all the austenite transforms regardless of strain rate. In the 5 and 6 Mn steels, where the retained austenite is moderately stable, strain induced transformation of austenite continues up to high plastic strain, providing a good balance of strength and ductility. At high strain rate, TS decreases slightly due to temperature rise, but at higher strain rates than 1 s, the strain rate sensitivity of flow stress in ferrite become prominent and the flow stress increases.

Probing deformation behavior of a refractory high-entropy alloy using neutron diffraction

Zhou, Y.*; Song, W.*; Zhang, F.*; Wu, Y.*; Lei, Z.*; Jiao, M.*; Zhang, X.*; Dong, J.*; Zhang, Y.*; Yang, M.*; et al.

Journal of Alloys and Compounds, 971, p.172635_1 - 172635_7, 2024/01

https://doi.org/10.1016/j.jallcom.2023.172635

The grain orientation-dependent lattice strain evolution of a (TiZrHfNb) refractory high-entropy alloy (HEA) during tensile loading has been investigated using neutron diffraction. The equivalent strain-hardening rate of each of the primary -oriented grain families was found to be relatively low, manifesting the macroscopically weak work-hardening ability of such a body-centered cubic (BCC)-structured HEA. This finding is indicative of a dislocation planar slip mode that is confined in a few single-slip planes and leads to in-plane softening by high pile-up stresses.

Development of a surrogate system of a plant dynamics simulation model and an abnormal situation identification system for nuclear power plants using deep neural networks

関 暁之; 吉川 雅紀; 西野宮 良太*; 沖田 将一朗; 高屋 茂; Yan, X.

Nuclear Technology, 12 Pages, 2024/00

https://doi.org/10.1080/00295450.2023.2273566

原子力プラントの安全な運転を支援するため、2種類のディープニューラルネットワーク(DNN)のシステムを構築した。一つは、原子力プラントの各種物理量についてシミュレーションよりも数桁少ない計算時間で推定するサロゲートシステム(SS)である。もう一つは、物理量から異常の原因となる外乱の状態を推定するシステム(ASIS)である。両システムとも、高温工学試験研究炉(HTTR)の挙動を様々なシナリオで再現することができる解析コード(ACCORD)から得られたデータを用いて学習を行った。DNNのモデルは、主要なハイパーパラメータを調整することにより構築された。これらの手順を経て、開発したシステムが高い精度で動作することを確認した。

Molecular dynamics analysis of reactor graphite for preparing thermal neutron scattering law

沖田 将一朗; 後藤 実

Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 10 Pages, 2023/10

The recently released JENDL-5 and ENDF/B-VIII.0 have adopted porosity-dependent thermal neutron scattering law (TSL) data for reactor graphite, and they improve neutronic calculation accuracy of criticality for graphite-moderated cores. Currently, we can only handle neutronic calculations for three graphite porosities of 0%, 10%, and 30%. The uncertainties associated with the difference between the porosity of actual reactor graphite (20%) and the porosity remains. Toward the future update of JENDL-5, we are planning to preparing new TSL data of reactor graphite. As a first step, it is essential to evalute phonon density state distribution of reactor graphite. In this study, in order to evalute it, molecular dynamic (MD) analysis is performed for three MD models: ideal crystalline graphite (Ideal model), 20%-porous reactor graphite with monoatomic random pore (Monoatomic random model), and 20%-porous reactor graphite with atomic cluster random pore (Cluster random model). The ideal crystalline graphite is modeled without any pores for reference. The 20%-porous reactor graphite with monoatomic random pore is modeled by randomly removing atoms from the ideal crystalline graphite. The 20%-porous reactor graphite with cluster random pore is modeled by randomly removing atomic clusters of approximately 2 nm in diameter from the ideal crystalline graphite. Their interatomic interactions are on the basis of Reactive Empirical Bond Order (REBO) potential. Velocity autocorrelation functions and phonon density of states distributions are calculated for these models. For validation, specific heat for each model is evaluated, and they are compred with experimental values.

高温ガス炉用SiC母材燃料コンパクトの作製に関する検討

河野 貴大*; 水田 直紀; 植田 祥平; 橘 幸男; 吉田 克己*

JAEA-Technology 2023-014, 37 Pages, 2023/08

JAEA-Technology-2023-014.pdf:2.35MB

現在用いられている高温ガス炉用燃料コンパクトは、被覆燃料粒子を黒鉛母材で焼き固めた黒鉛母材燃料コンパクトである。これに対して、SiC母材燃料コンパクトは、母材を従来の黒鉛から新たに炭化ケイ素に換えたものである。高温ガス炉用燃料コンパクトを従来の黒鉛母材燃料コンパクトからSiC母材燃料コンパクトに換えることで、高温ガス炉の出力密度等の性能向上が期待される。本研究では、高温ガス炉用燃料コンパクトに適用するための焼成条件を選定し、試作したSiCの密度や熱伝導率を測定した。

Relationship between internal stress distribution and microstructure in a suspension-sprayed thermal barrier coating with a columnar structure

山崎 泰広*; 篠宮 啓介*; 奥村 忠晴*; 鈴木 賢治*; 菖蒲 敬久; 中村 唯我*

Quantum Beam Science (Internet), 7(2), p.14_1 - 14_12, 2023/05

https://doi.org/10.3390/qubs7020014

The suspension plasma spray (SPS) technique has attracted attention because of its various microstructures, which can be achieved by mixing submicron spray particles with a solvent to form a suspension. Thermal barrier coatings (TBCs) with a columnar structure, which might achieve high strain tolerance, can be obtained using the SPS technique. In this study, the internal stress distribution of the SPS-TBC with different columnar structures was evaluated by hybrid measurement using high-energy synchrotron X-ray diffraction analysis and laboratory low-energy X-rays. The effect of microstructure on the internal stress distribution of the SPS-TBC was discussed on the basis of the experimental results. In addition, the in-plane internal stress was decreased by decreasing the column diameter. The thin columnar microstructure of the SPS-TBC has superior strain tolerance. The internal stresses in the column of the SPS-TBC are periodic decrements caused by stress relaxation in porous layers.