Investigation of laser shock peening effects on residual stress state and fatigue performance of titanium alloys

Highlights: ► Effect of laser peening without coating (LPwC) on fatigue life of Ti alloys was studied. ► High cycle fatigue life was prolonged in Ti–2.5Cu and LCB and deteriorated in Ti-54M. ► Results were mainly interpreted by residual stresses and surface morphology. ► Residual stress is thermally more stable after LPwC than that after shot peeing. ► Surface vaporization due to LPwC results in very rough surface. - Abstract: Laser shock peening can potentially enhance fatigue life of titanium components by inducing compressive residual stresses in surface layers much deeper than caused by traditional shot peening (SP). In the present study, the high cycle fatigue (HCF) performance of α Ti-alloy Ti–2.5Cu, (α + β) Ti-alloy TIMETAL 54M and the metastable β Ti-alloy TIMETAL LCB was investigated after laser shock peening without coating (LPwC). The fatigue results were interpreted by examining the changes of surface morphology, microhardness and residual stress generated in the surface layer. Furthermore, thermal stability of residual stresses in aged Ti–2.5Cu, as an example, was evaluated after annealing LPwC-treated material at various elevated temperatures and exposure times by applying a Zener–Wert–Avrami approach. The depth profiles of residual stresses were obtained by means of synchrotron X-ray diffraction or by incremental hole drilling method. Results revealed that the HCF performance of Ti–2.5Cu and TIMETAL LCB was markedly improved after LPwC, while it was deteriorated in TIMETAL 54M. Compared to LPwC, better 107 fatigue strength of Ti–2.5Cu was obtained after ball-burnishing (BB). Moreover, LPwC-induced residual stresses are thermally more stable than shot peening-induced ones.