Residual stress relaxation and its effects on the fatigue properties of Ti6Al4V alloy strengthened by warm laser peening

A method combining experiment and simulation was used in this paper to study the effects of warm laser peening (WLP) on the residual stress relaxation (RSR) in Ti6Al4V titanium alloy. Moreover, the effects of RSR on fatigue properties and its mechanism were both revealed. Laser peening experiments were conducted at room temperature (RT-LP) and elevated temperature (300 °C-WLP). Then the yield strengths of specimens were obtained through tensile experiments and their improvement induced by WLP was analyzed by microstructures. A finite element analysis was used to research the effects of RT-LP and 300 °C-WLP on the RSR during fatigue. Finally, the fatigue life and fracture microstructures were both measured and analyzed. The results indicate that the severe plastic strain induced by 300 °C-WLP results in lots of crossed acicular α phases with a short spacing, which promotes the interactions between α phases and leads to an increasing dislocation density. Therefore, the yield strength of 300 °C-WLPed specimens is much greater than RT-LPed samples based on the Hall-Petch relations. Besides, the simulated results show that the extended yield strength of 300 °C-WLPed specimens significantly decreases the dσ/dε during fatigue and thus reduces the relaxation of CRS. Moreover, it can be found that the fatigue life of 300 °C-WLPed specimens is subjected to an significant increase, which can be attributed to the increasing finished crack lengths and the decreasing RSR.