| 研究開始時の研究の概要 |
This study helps to evaluate the initial damage of Ni-based alloys under creep-fatigue loading at elevated temperatures more accurately to ensure the reliability and stability of thermal power plants.The damage of Ni-based alloys under creep-fatigue loading cannot be quantitatively evaluated so far. While, we have found that the generation of initial cracking takes a large shear of its total lifetime. In this study, various testing methods will be used to establish a theoretical model for evaluating the mechanism of initial damage generated at grain boundaries of Ni-based alloys.
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| 研究実績の概要 |
In last year's research, an important drawback of our previously proposed stress-induced acceleration of atom diffusion (modified Arrhenius equation) was found, namely the difficulty in quantitatively estimating the stress at the crack initiation region, at least with our existing experimental methods. Difficult to estimate even on ambiguous scales. The reasons are very complicated. First, it is difficult to define its influence range. Second, it is difficult to quantitatively distinguish between the stress concentration caused by external load and the stress concentration caused by lattice mismatch at the grain boundary. Third, each grain has its own uniqueness, that is, the uniqueness of its orientation and the way it combines with adjacent crystals. In addition, in the materials with smaller crystal diameters, it is difficult to compare the crystal parameters of the same set of adjacent crystals multiple times by conducting intermittent creep for creep-fatigue test due to oxidation during each loading process and subsequent polishing losses. Currently, our group are trying to use strain instead of stress as the influencing parameter of the modified Arrhenius formula. Some progress on the quantitative evaluation of creep crack initiation of SUS316 material has been achieved, and in future studies, we may consider extending it to other material to verify the feasibility of this idea.
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