open access

https://doi.org/10.14943/doctoral.k16340

https://hdl.handle.net/2115/95673

原子炉用CoフリーFCCミディアムエントロピー合金の照射下における微細組織変化と機械的特性に及ぼすヘリウムと水素の影響

英語

2025-03-25

Hokkaido University

XV, 84p.

The research and development of advanced nuclear power systems are critically important for the commercialization of next generation nuclear reactors. New structural materials with high corrosion and irradiation resistance are urgently required for extended use at high temperatures and high doses. In recent years, medium and/or high-entropy alloys (M/HEAs) have garnered significant attention due to their attractive mechanical properties. The high strength, ductility, and corrosion resistance make HEAs potential candidates for structural applications in high temperature fission or fusion reactors. Heavy ion irradiation has been intensively used to investigate the irradiation effects on HEAs including swelling, hardening, and phase stability. However, one of particular concern is the simultaneous production of helium and hydrogen that have a strong impact on the microstructure evolution of irradiated materials. Typically, they may cause additional swelling and embrittlement of materials. In this study, the performance of four different Cr-Fe-Mn-Ni HEAs under irradiation, including He and H effect on the microstructure evolution and mechanical properties, are also investigated. Firstly, a group of Co-free medium entropy alloys(MEAs): Cr0.65FeMnNi, Cr0.8FeMnNi, Cr0.8FeMn1.3Ni, Cr0.8FeMn1.3Ni1.3 were prepared by arc melting. After annealing at 1100 °C for 48 hours, the samples were cold-rolled, followed by recrystallization at 1000 °C for 4 hours. Electron backscattered diffraction (EBSD), tensile test and nano-indentation test was conducted to characterize the microstructure and the mechanical properties for each alloy. The elevated Mn content within this alloy induced a high atomic size difference within the material, inducing highest hardness and smallest grain size in Cr0.8FeMn1.3Ni. The high grain boundary strengening and solid solution strengthening result in the high strength of Cr0.8FeMn1.3Ni. Secondly, in order to understand He injection amount effect on the microstructure evolution in HEAs, Cr0.8FeMnNi and 316L were irradiated with Fe2+ at a temperature of 500 ℃ with different He+ preinjection amount. Transmission electron microscopy was used to characterize the irradiation-induced defects. As He injection amount increased, the binding energy of the self-interstitial atom (SIA) to the He-V complex decreased. This reduction result in the increase of the SIA in the matrix, affecting the evolution of point defects. Thirdly, Cr0.8FeMnNi and 316L is irradiated with single beam (Fe3+ ), dual beam (Fe3++He+ ) and triple beam (Fe3++He++H + ) at 500 ℃. He and H effect on irradiation induced hardening and swelling on HEAs and 316L is studied. The nanoindentation test showed that MEAs showed higher irradiation hardening resistance than 316L. The microstructure characteration results indicates that under single beam irradiation, large cavities formed in Cr0.8FeMnNi. Small bubbles with high density were found in dual and triple beam irradiated Cr0.8FeMnNi and 316L. He enhanced the nucleation and H can enhanced the growth of bubbles. The interaction bewteen He and vacancy could be weaker in Cr0.8FeMnNi. This work indicated that Mn content can affect the lattice distortion of MEA, affecting the microstructure and mechanical property. The pre-injected He amount can affect the binding energy of SIA to He-V cluster. The decrease of the binding energy of SIA to He-V complex can affect the point defect evolution. The bulk irradiation showed that He enhanced the nucleation and H can enhanced the growth of bubbles in MEAs.

2025-03-25

甲第16340号

博士(工学)

(主査) 教授 橋本 直幸, 教授 三浦 誠司, 准教授 坂口 紀史, 准教授 礒部 繁人

工学院（材料科学専攻）

博士論文

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