Microstructural and thermal relaxation of residual stress in dual peened TA15 titanium alloy fabricated by SLM

TA15 (Ti-6Al-2Zr-1Mo-1 V) is a near-α titanium alloy widely used in aerospace applications due to its high specific strength and corrosion resistance. However, like other titanium alloys, TA15 faces significant manufacturing challenges. Selective Laser Melting (SLM), a high-precision additive manufacturing technique, enables the efficient production of complex components but also introduces issues such as tensile residual stress. This study investigates the effects of dual shot peening on the residual stress and microstructure of SLM-fabricated TA15 alloy, and analyzes the thermal relaxation behavior post-peening. The results indicate that shot peening induces a compressive residual stress (CRS) field near the material surface and significantly refines the grains in the deformed layer, resulting in the formation of nanocrystals. The introduction of low-intensity ceramic shots in dual shot peening effectively improves the surface quality and enhances CRS, although it has minimal impact on grain size and microstrain. Using the ZWA model, the activation energy for thermal relaxation of residual stress and microstrain was determined, revealing that their relaxation behavior is controlled by thermally activated diffusion of point defects, especially vacancies. Post-thermal exposure, extensive dislocation annihilation and grain growth were observed in the deformed layer, with recrystallized grain size increasing with annealing temperature and depth.