Effect of low-temperature annealing on microstructure and mechanical properties of Ti6Al4V produced by laser shock peening

In this study, a combination of laser shock peening (LSP) and low-temperature annealing (LTA) was used to modulate the microstructures of Ti6Al4V, which can achieve an optimal combination of strength and plasticity. Microstructure observations showed that after LSP treatment, serious plastic deformation and grain refinement occurred. This resulted in the formation of non-equilibrium grain boundaries (GBs) composed of dislocations, twins, and martensite transformation. After LTA treatment, the dislocation density decreased as it rearranged, resulting in GB relaxation. The GB state can change from non-equilibrium to equilibrium. Additionally, LTA treatment can increase the activation energy and facilitate element diffusion from high to low concentration. The decrease in dislocation density and element diffusion results in GB with low excess energy, increasing the stability of the microstructural. The LSP composite LTA treatment showed a high tensile strength of 994 MPa and an excellent elongation of 17.4% compared to the untreated specimen. Excellent microstructure stability and mechanical properties are achieved in Ti6Al4V after combined post-treatment of LSP and LTA.