Abstract
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 107 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 103 to 105 cycles are the same for both materials.
The fracture appearances fatigued at around 106 cycles showed internal fractures originating from the flat facets of austenite grains for both materials. The difference in fatigue strength at 107 cycles between the fine and coarse grain materials could be explained in terms of the sizes of the facets from which the fractures originated.
