Thermal stress relaxation in shot peened and laser peened nickel-based superalloy

The effects of cold work produced by peening processes in residual stress relaxation under elevated temperatures were investigated. Two types of peening processes namely shot peening and laser peening were used to generate different amount of cold work and residual stresses in the study. Characterisation of residual stress induced by cold working were carried out using X-ray diffraction coupled with electrochemical polishing method to measure the variation of residual stress with depth. Residual stresses in shot peened samples were observed to relax more rapidly than that of laser peened ones when subjected to thermal exposure. The data collected from the experimental investigation was then used to build a correlation function to model the effects of cold work on residual stress relaxation. A parameter describing cold work’s contribution to stress relaxation is introduced into the well-known Zener-WertAvrami(ZWA) model. The model was validated against experimental measurements and showed good agreement in both shot peened and laser peened samples.