Explication of the degradation mechanism of the strength of heat-resistant alloys under random loading at elevated temperatures and the establishment of the prediction method of their lifetime

高温随机载荷下耐热合金强度退化机理的解释及寿命预测方法的建立

基本信息

批准号：
21F50350
负责人：
三浦英生
金额：
$ 0.64万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for JSPS Fellows
财政年份：
2021
资助国家：
日本
起止时间：
2021-11-18 至 2023-03-31
项目状态：
已结题

项目摘要

The main objectives of this research are 1) Clarification of the acceleration mechanism of the degradation of materials under creep-fatigue loading at elevated temperatures, and 2) Establishment of the quantitative evaluation method of the damage of the materials under random load conditions. Original small dumbbell-shape specimens were manufactured for both the observation of the degradation process under the distribution of the applied load and the direct observation of the change of the local crystallinity of the alloy in a scanning electron microscope. The degradation process of the crystallinity of the representative heat-resistant alloy, Ni-base superalloy, under creep-fatigue loading at elevated temperatures was monitored continuously by using our original intermittent micro tensile test method with electron microscopy. The degradation process of the crystallinity and strength of the material was continuously observed, and it was explicated by applying the modified Arrhenius equation by considering the effect of mechanical stress on the local decrease in the activation energy of atomic diffusion. it was also found that the accumulation of vacancies and dislocations was accelerated only around grain boundaries and thus, the initiation time of intergranular cracking became shorter when the strain rate during loading and unloading became faster. The main reason for the acceleration was found to be the activation of viscoelasticity of the alloy at the elevated temperature.

本研究的主要目标是1）阐明高温蠕变疲劳载荷下材料降解的加速机制，2）建立随机载荷条件下材料损伤的定量评估方法。制作原始的小哑铃形样品，既可以观察施加载荷分布下的降解过程，也可以在扫描电子显微镜下直接观察合金局部结晶度的变化。通过使用我们原创的电子显微镜间歇微拉伸试验方法，连续监测代表性耐热合金镍基高温合金在高温蠕变疲劳载荷下结晶度的退化过程。连续观察材料结晶度和强度的退化过程，并考虑机械应力对原子扩散活化能局部降低的影响，应用修正的阿伦尼乌斯方程对其进行了解释。研究还发现，空位和位错的积累仅在晶界周围加速，因此，当加载和卸载期间的应变速率变快时，晶间裂纹的萌生时间变短。发现加速的主要原因是合金在高温下粘弹性的激活。