Internal Fracture of Nickel-base Alloy718 in High Temperature Fatigue

摘要

We investigated the fatigue properties at high temperatures of fine grain and coarse grain nickel-base Alloy718. In the fine grain material, the fatigue strength normalized by the tensile strength was 0.51 at 10~7 cycles. In contrast, the fatigue strength of the coarse grain material was 0.32 at the same cycles, although the fatigue strengths in the range from 10~3 to 10~5 cycles are the same for both materials. The fracture appearances fatigued at around 10~6 cycles showed internal fractures originating from the flat facets of austenite grains for both materials. The difference in fatigue strength at 10~7 cycles between the fine and coarse grain materials could be explained in terms of the sizes of the facets from which the fractures originated.