Observation of Phase Transformation in Laser Peening Process Using X-ray Free-Electron Laser

Abstract

This article reviews our experimental investigation of the phase transformation process of 304 austenitic stainless steel (SUS304) in the laser peening process. An optical laser pump–X-ray free-electron laser probe in-situ time-resolved X-ray diffraction measurement reveals the formation process of α ′-martensite from γ -austenite of SUS304 under shock compression and release, which occur during the laser peening process. The result indicates that fast tensile strain rate deformation, arising from shock pressure release waves, drives a considerable amount of the transformation to transient ε -martensite from γ - austenite, where the transient ε -martensite acts as an intermediate phase of the transformation to α ′-martensite.