On the relationship between microstructure and residual stress in laser-shock-peened Ti-6Al-4V

Abstract

The relationship between residual stress and microstructure evolution during laser shock peening (LSP) of Ti-6Al-4V was investigated. To this end, the program material was processed using a 5-J Q-switched Nd:YAG laser with a wavelength of 1064 nm and a pulse duration of 20 ns. The residual stresses developed during LSP were determined by means of the incremental-hole-drilling method, and the corresponding microstructures were established using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). From these observations, it was deduced that deformation and the resulting microstructure evolution during LSP were controlled by an inhibition of dislocation cross-slip, which, in turn, was attributed to the extremely short duration of the process. Hence, it was surmised that the unique residual-stress state generated during LSP is associated with two intrinsic characteristics of this technique, i.e., the very high imposed energy and the extremely short time scale. The large and non-uniform mechanical energy input gives rise to the residual stresses while the limited time span prevents stress relief via dislocation cross slip and climb.