The fatigue crack nucleation mechanism of Ti-2Al-2.5Zr alloy was investigated using the coupling method of quasi in-situ tests with crystal plasticity (CP) simulation. The constitutive parameters in the CP model were validated by digital image correlation based on scanning electron microscope (SEM-DIC). It was found that the transgranular and intergranular cracks nucleated inside grains and at grain boundaries (GBs), respectively, due to slip intrusions/extrusions along prismatic planes with highest SF_pris. values, while quasi transgranular cracks were induced by the adjacent microstructure or cracks. The angle Ω between the sample surface and the slip direction of slip planes where the transgranular cracks nucleated was within the range of 20–55°. Three factors for predicting intergranular cracks were identified, and the slip shearing mechanism of GBs was proposed. The CP results revealed that a significant plastic strain difference was generated at GBs where intergranular cracks nucleated. The band averaging method showed better prediction ability than the grain averaging method, and a unified fatigue indicator parameter (FIP) combining the accumulated plastic strain, the strain incompatibility parameter (SIP), and the abovementioned crack prediction factors, was proposed, which improved the unified prediction ability for both transgranular and intergranular cracks.

采用准原位试验与晶体塑性(CP)模拟耦合的方法研究了Ti-2Al-2.5Zr合金的疲劳裂纹形核机制。CP模型中的本构参数通过基于扫描电子显微镜（SEM-DIC）的数字图像相关性进行验证。结果发现，由于沿具有最高 SF 棱柱的棱柱面的滑移侵入/挤压，穿晶裂纹和晶间裂纹分别在晶粒内部和晶界 (GB) 处成核_。值，而准穿晶裂纹是由相邻的微观结构或裂纹引起的。试样表面与穿晶裂纹成核滑移面滑移方向的夹角Ω在20°～55°范围内。确定了预测晶间裂纹的三个因素，并提出了 GB 的滑移剪切机制。CP 结果表明，在晶间裂纹成核的 GB 处产生了显着的塑性应变差异。带平均法显示出比晶粒平均法更好的预测能力，并提出了结合累积塑性应变、应变不相容参数（SIP）和上述裂纹预测因素的统一疲劳指标参数（FIP），