Abstract:

Addressing grain size effect on the initiation and propagation behavior of small fatigue crack of GH4169 alloy at room temperature and 650 ℃. Changing the grain size of specimen by solid solution heat treated at 960 ℃、1 010 ℃、1 020 ℃、1 050 ℃ about 1 h. The microstructures after different heat treatments are investigated by optical microscope(OM). The replica method is used to measure the crack length. Results show that there are transition of fatigue crack initiation mechanism and crack propagation mode between fine-grained material and coarse-grained material at both room temperature and 650 ℃. Crack propagation rates are almost constant in small crack stages at both room temperature and 650 ℃. The variations of average grain size have almost no effect on the small crack rates at room temperature. But at 650 ℃ small crack propagation rates increase with the increase of average grain size. Once the length of surface cracks reach a critical size, the cracks propagate quickly. At room temperature the critical sizes of surface crack of specimens with different average grain size are almost uniform. However the critical size of surface cracks increase with the increase of average grain size.

Key words: 650 ℃, fatigue, GH4169, grain size, room temperature, small crack