Surface profile evolution and fatigue crack initiation in Sanicro 25 steel at room temperature

Evolution of the surface profile in room temperature cyclic loading has been studied in high alloy austenitic Sanicro 25 stainless steel. The localization of the cyclic plastic strain into persistent slip bands in the volume of the material leads to the formation of the specific surface relief in the form of persistent slip markings (PSMs) consisting of extrusions and intrusions. Evolution of the shape of PSMs was studied during interruption of cycling using SEM and FIB techniques. Three-dimensional information about the PSMs profiles was obtained. The profiles of both extrusions and intrusions and their evolution during cyclic loading were assessed. Generally extrusions grow, intrusions deepen and fatigue cracks initiate from the tip of the deepest intrusions. The experimental observations were compared and discussed in relation to existing physical models of surface relief formation and fatigue crack initiation.