Intergranular fatigue crack nucleation has been reported to occur commonly at high angle grain boundaries (HAGBs) but seldom at low angle GBs (LAGBs) during persistent slip band (PSB)-GB interactions. However, the mechanistic understanding of the role of GB misorientation angles in affecting the GB fatigue cracking remains limited due to the lack of quantitative descriptions. Here a theoretical framework based on the competition between dislocation transmission across GB and GB cracking is established for investigating the GB fatigue crack nucleation. We show that, HAGBs usually provide higher resistances to dislocation transmissions compared with LAGBs, causing a more significant dislocation pile-up and stress concentration, which facilitates the GB crack nucleation. But the quantitative analysis indicates that even at HAGBs with poor plastic compatibility, the critical stress of GB cracking is much larger than the critical transmission stress. This demonstrates the crucial role of GB fatigue damage accumulation, which is associated with PSB extrusion growth, in promoting GB crack nucleation. In this study, the critical stress of dislocation transmission is derived in terms of the energy balance, and the nucleation criterion of GB crack is formulated using the fracture theory, both of which display the dependence on GB misorientation angles and grain sizes. It is found that the GB fatigue cracks preferentially nucleate at HAGBs with poor plastic compatibility and large grain sizes. The competition between dislocation transmission and GB cracking at varying fatigue cycles are also discussed. This theoretical framework offers quantitative analyses for the GB crack nucleation during PSB–GB interactions, clarifies the role of microstructures in affecting the critical cycles of GB cracking, and might offer important guidelines for designing fatigue-resistant metallic materials.

据报道，在持久滑移带 (PSB)-GB 相互作用期间，晶间疲劳裂纹成核通常发生在高角度晶界 (HAGB)，但很少发生在低角度晶界 (LAGB)。然而，由于缺乏定量描述，对 GB 取向差角在影响 GB 疲劳开裂中的作用的机械理解仍然有限。这里建立了一个基于晶界位错传输与晶界开裂之间竞争的理论框架，用于研究晶界疲劳裂纹形核。我们表明，与 LAGB 相比，HAGB 通常提供更高的位错传输阻力，导致更显着的位错堆积和应力集中，从而促进 GB 裂纹形核。但定量分析表明，即使在塑性相容性较差的 HAGBs 中，GB 开裂的临界应力也远大于临界传输应力。这证明了与 PSB 挤压生长相关的 GB 疲劳损伤累积在促进 GB 裂纹形核中的关键作用。在这项研究中，位错传输的临界应力是从能量平衡的角度推导的，并且 GB 裂纹的成核标准是使用断裂理论制定的，两者都显示了对 GB 取向差角和晶粒尺寸的依赖性。发现GB疲劳裂纹优先在塑性相容性差、晶粒尺寸大的HAGBs上形核。还讨论了不同疲劳循环下位错传输和 GB 开裂之间的竞争。