In the present study, fatigue damage evolution of Inconel 617 at 600 °C and 700 °C was investigated by using an in situ scanning electron microscope (SEM) fatigue test. The fatigue crack initiation and propagation processes were directly observed and recorded online. Fractography and microstructure analyses were performed to further reveal the mechanism of high-temperature failure. Experimental results showed that Inconel 617 was not sensitive to an artificial notch even if the curvature reached approximately a hundred microns, and it was more vulnerable to intergranular fracture. This alloy showed multiple crack initiation and propagation behavior at high temperatures. Multiple crack initiation sites did not occur in the same planes, and the number of crack initiation sites increased with increasing environmental temperature. Intergranular cracking behavior was observed in the near surface region, and transgranular crack initiation and propagation were mainly observed in the interior. Coarsening and discrete M₂₃C₆-type carbides formed at grain boundaries were the main factors responsible for intergranular cracking. The twin boundary (TB) was directly observed as the crack initiation site, and it retarded crack propagation along the TB and changed the crack propagation mode.

在本研究中，Inconel 617 在 600 °C 和 700 °C 下的疲劳损伤演变通过使用原位扫描电子显微镜 (SEM) 疲劳测试。直接在线观察和记录疲劳裂纹萌生和扩展过程。进行断口和微观结构分析以进一步揭示高温失效的机制。实验结果表明，即使曲率达到约一百微米，Inconel 617 对人工缺口也不敏感，更容易发生晶间断裂。该合金在高温下表现出多重裂纹萌生和扩展行为。同一平面内不会出现多个裂纹萌生点，且裂纹萌生点的数量随着环境温度的升高而增加。在近表面区域观察到晶间开裂行为，主要在内部观察到穿晶裂纹的萌生和扩展。粗化和离散 M晶界处形成的₂₃ C ₆型碳化物是导致晶间开裂的主要因素。双晶界（TB）被直接观察为裂纹萌生点，它延缓了裂纹沿TB的传播并改变了裂纹扩展模式。