TiAl基合金的拉伸疲劳断裂机理

Fracture Mechanism of Tensile Fatigue for TiAl Based Alloys

对TiAl基合金试样进行了拉伸疲劳试验,并进行了断口观察,探讨了该合金的拉伸疲劳断裂的机理。结果表明:该合金断口上有很明显的河流花纹走向和唯一的起裂源,断口以沿层面为主,穿层面只占少数;裂纹源通常位于断口表面的角落处,然后裂纹沿多个方向解理扩展至试样边缘,最后发生脆性解理断裂;其断裂机理是在疲劳拉伸载荷作用下,在应力较高处沿层裂纹开始出现,裂纹在应力循环作用下不断扩展,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(即满足Griffiths条件)时,试样整体解理断裂。

TiAl based alloys were tested in tensile fatigue experiment, and their facture morphology was observed to study the faeture mechanism of tensile fatigue. The results show that there were orientations of river pattern and sole crack initiation origin on the fracture of the alloy. The fracture surface was composed of a lot of inter-lamellas which were dominant and little trans lamellas. The crack initiation origin was located at the corner of fracture surface, and the cracks propagated along different orientations to the edges of the specimen, then the specimen fractured. The fracture mechanism is described as following： several interlamellar cracks successively initiate under tensile fatigue loading at a highly stressed site, then the fatigue crack extends continuously by the cycling of fatigue stress. When the length of fatigue crack reaches the critical crack length matching to the loading stress, which means the Griffiths condition, the cleavage fracture of specimen will take place.