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

在去年的研究中，我们发现了先前提出的应力诱导原子扩散加速（修正Arrhenius方程）的一个重要缺陷，即难以定量估计裂纹起裂区域的应力，至少用我们现有的实验方法是如此。即使在模棱两可的尺度上也很难估计。原因很复杂。首先，其影响范围难以界定。其次，难以定量区分外载荷引起的应力集中和晶界处晶格失配引起的应力集中。第三，每个晶粒都有自己的独特性，即其取向的独特性以及与相邻晶体结合方式的独特性。此外，在晶体直径较小的材料中，由于每次加载过程中的氧化和随后的抛光损失，很难通过间歇蠕变对同一组相邻晶体的晶体参数进行多次比较进行蠕变疲劳试验。目前，我们小组正在尝试用应变代替应力作为修正Arrhenius公式的影响参数。在SUS316材料蠕变裂纹起裂的定量评价方面已经取得了一些进展，在未来的研究中，我们可以考虑将其推广到其他材料，以验证这一思路的可行性。

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.