Fatigue damage monitoring of laser surface treated steel by X-ray diffraction methods

Abstract

The evolution of fatigue damage in an austenitic stainless steel was investigated by metallographic and X-ray diffraction (XRD) methods. The experimental results confirm a previously developed idea based on X-ray line breadth measurements. According to this idea, the operating mechanism for fatigue damage is the progressive work hardening of the material which takes place preferentially at the surface and advances gradually into the bulk. Fatigue fracture is related to the attainment of a critical work hardening level at the surface. The so called integral breadth of the XRD line was taken as an estimate of work hardening. In the present work the X-ray line integral breadth was used to monitor the accumulated work hardening of laser surface treated and untreated specimens during fatigueand is proposed as a non-destructive fatigue damage parameter. It is also shown that the map of the surface damage resulting from integral breadth measurementson broken specimens gives iriformation about the microstructure and fatigue damage evolution. Particularly, the change in the damage accumulation after laser surface treatment is related to the microstructural changes caused by the treatment.