中文摘要：

研究了GH4169高温合金在高温条件下小裂纹的萌生和扩展行为.选用单边缺口试样,在650℃下进行应力比R为0.1,频率为0.5Hz的高温低频疲劳试验,采用覆膜法记录裂纹长度.结果表明,在试样缺口根部只存在一条主裂纹,且萌生于夹杂物附近,疲劳小裂纹扩展阶段占全寿命一半以上.利用SEM对断口进行断面微观分析,发现疲劳小裂纹倾向于以半椭圆形向试样内部扩展.同裂纹扩展速率曲线相对比,发现在断裂模式转变处裂纹扩展发生停滞现象,且在裂纹扩展完全由穿晶扩展转变为沿晶扩展之后,裂纹快速长大,导致试样断裂.

英文摘要：

The initiation and propagation behavior of small fatigue crack of GH4169 alloy at 650℃ were studied. The SENT （single- edge-notch-tension） specimen was used in fatigue test. The frequency was 0.5Hz and the stress ratio was kept to be 0.1. The replica method was used to measure the crack length. Results show that only one main crack initiated from the inclusion is observed from the root of the notch. The life of small crack growth is more than half of the total fatigue life of specimen. The small fatigue crack is prone to propagate into the interior of specimen with semi-elliptical shape, which can be reflected from the fractography analysis. Combined with the observation from the crack growth rate curve, it can be concluded that the crack growth rest plays an important role on the tran- sition of fracture mode. When the crack propagation mode completely is transformed from transgranular to intergranular, the crack growth rate will be increased rapidly, leading to the final fracture of the specimen.