Clarification of the initial damage mechanism of Ni-based superalloy under creep-fatigue loading at elevated temperature

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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.