第一代单晶高温合金中温高应力幅下的疲劳裂纹萌生行为

通过应力控制的疲劳实验探究第一代镍基单晶高温合金DD413在中温(760℃)高应力幅下的疲劳裂纹萌生行为，并使用扫描电子显微镜观察和表征了疲劳样品的断口形貌和纵截面的显微组织。结果表明：在高应力幅条件下，疲劳裂纹主要萌生于表面开裂的块状碳化物和次表面开裂的骨架状碳化物。在疲劳过程中，氧化和循环加载的共同作用使样品表面的碳化物都发生了开裂。在样品的次表面，只有位于表面微裂纹扩展路径上的碳化物发生开裂，其原因也与氧化和循环加载有关。样品表面产生的微裂纹，是次表面碳化物发生氧化所需氧气的运输通道。在疲劳的早期阶段碳化物即发生开裂并产生微裂纹，最终使样品发生疲劳断裂。

Fatigue Crack Initiation Behavior at Intermediate Temperature under High Stress Amplitude for Single Crystal Superalloy DD413

The fatigue crack initiation behavior of a single crystal superalloy DD413 was investigated under high stress amplitude at intermediate temperature. The fracture surfaces and longitudinal section morphologies of the test specimens were characterized by scanning electron microscope (SEM). It was found that fatigue cracks mostly initiate from the cracked blocky carbides on the surface as well as the cracked skeleton-like carbides at subsurface. All the carbides on the surface of testing specimen crack due to the combined effect of oxidation and cyclic loading. Besides, at the subsurface of testing specimen, the carbides located on the propagation path of a micro-crack can crack as a result of oxidation and cyclic loading. The micro-crack connected to the surface in the specimen is the transportation channel of oxygen for the oxidation of the carbides at the subsurface. Carbides cracked and the micro-crack initiated at the early stage of fatigue, which induced the final failure.