TiAl基合金弯曲疲劳的断裂机制

Fracture Mechanism of Bending Fatigue for TiAl-Based Alloys

通过对弯曲疲劳断裂宏观试验结果以及相应的卸载表面观察和断口观察分析研究,发现在疲劳加载的过程中,首先在缺口根部产生裂纹,裂纹在应力循环的作用下不断扩展,直至疲劳裂纹的长度达到与疲劳外加力所匹配的临界裂纹长度时,突然发生整体解理断裂。在一定应力下的疲劳弯曲加载试验中,随着循环次数的增加,产生的裂纹变长,即产生的损伤严重,疲劳区域变宽,其断裂机制是疲劳区各裂纹单向扩展,解理区起裂源分散扩展直至断裂。对于循环次数较小的材料,其断裂机制是具有发散扩展路径的起裂源直接产生于缺口根部,然后分散扩展直至断裂,在其扩展的路径上并不因疲劳区与解理区而有任何的不同。

Based on the results of notch 3PB fatigue tests and the observation of metallographic surfaces and fracture surfaces, it is found that for fatigue bending tests, the fatigue crack initiated and extended directly from the notch root, then extended step by step by the fatigue bending loads. When a crack extended to the length, which acts as a Griffiths crack and matches the loading stress, the crack propagated catastrophically through entire specimen. In the fatigue bending tests at the certain stress amplitude values, the crack length increased with increasing of fatigue unloading cycles, and the damage produced by fatigue process increased, the fatigue regions became wider, the fracture mechanism is that the fatigue regions propagate along a single orientation, the cleavage regions propagate dispersedly to different orientations. However, for shorter fatigue cycles the fracture mechanism is that initiation origins are produced at the notch root, then propagate dispersedly to final fracture. No any differences appear between the fatigue and the cleavage regions on the propagation path.