Effect of process temperature on mechanical properties of Ti6Al4V titanium alloy with warm laser shock peening

Warm laser shock peening (WLSP) is a thermomechanical strengthening technique with tempering treatment during laser shock peening (LSP) to optimize the mechanical properties of a metallic material. In WLSP, processing temperature plays a key role in regulating the final product's mechanical properties. In this work, Ti6Al4V titanium alloy is used to evaluate effect of temperature on mechanical properties during warm laser shock peening. The compressive residual stress (CRS) generated by WLSP at different temperature was measured by X-ray diffraction (XRD) and the surface hardness was investigated to reveal the surface strength features under different heat treatments as well. It was found that regardless of which temperature applied during the WLSP process, the treated specimens all displayed highamplitude CRS on the surface or in depth, but the surface peak CRS decreases gradually as temperature increases. Specially, when the WLP temperature exceeded 250°C, the decreasing slope raised. The CRS affected width increased first, and then decreased with the increases of temperature. The maximum CRS affected width was about 6.25 mm, appearing at a temperature of 250 °C. For the affected depth of CRS, firstly, as the temperature increases from 20 to 250 °C, the thickness of affected layer rises with temperature. However, when the temperature exceeds 300°C, the affected depth of CRS sharply declines. In addition, the WLSP technology could improve the hardness of Ti6Al4V titanium alloy from 389 HV at room temperature to 418 HV at 350 °C.