Influence of Microstructure on Subsurface Fatigue Crack Generation and Its High-cycle Fatigue Strength

摘要

The low fatigue resistance of high strength alloys in the high cycle regime is related to the subsurface crack generation, especially at the positive mean stresses.[1] This mode of failure is favored by the coarse microstructure. Both the refinement in microstructure and the introduction of movable dislocations on various kinds of slip systems resulted in a higher fatigue resistance to this mode of failure as well as a tendency to promote surface crack initiation as slip processes became more active at the higher stress levels [2]. For a group of metals with high stacking fault energy, on the other hand, the refinement in microstructure by a sever plastic deformation sometimes causes the subsurface fatigue crack initiation with increase of yield stress.[3] Therefore, cyclic softening itself is not substantial for the subsurface crack generation, but becomes a specific incompatibility at the grain boundary due to a planar slip in only the weak grain. The present paper is concerned with discussing a systematical understanding of the subsurface fatigue crack generation in high strength alloys.