Investigation on mechanical properties and microstructural evolution of TC6 titanium alloy subjected to laser peening at cryogenic temperature

The aim of this study was to investigate the influence of the synergistic function of cryogenic temperature and ultrahigh strain rate deformation during the process of Cryogenic Laser Peening (CLP) on the mechanical properties and microstructural evolution of TC6 titanium alloy. The measurements of tensile properties at room and elevated temperatures, as well as micro-hardness on the cross-sectional direction were carried out. Meanwhile, the microstructural evolution was characterizated by Electron Backscattered Diffraction (EBSD) analysis and Transmission Electron Microscopy (TEM) observation. The experimental results demonstrated that cryogenic laser peening could significantly improve the strength and ductility, as well as the stability at elevated temperature condition of TC6 titanium alloy. At the same time, cryogenic laser peening could provide higher surface micro-hardness than room temperature laser peening (RT-LP), the surface micro-hardness of the specimen subjected to cryogenic laser peening increased by 4.86% than that of the specimen treated by room temperature laser peening. Additionally, cryogenic laser peening could generate finer grains and higher-density of dislocation structures, while large numbers of sub-grains and mechanical twins were also observed in the surface layer. Finally, the microscopic strengthening mechanism of cryogenic laser peening for better mechanical properties on TC6 titanium alloy was also analyzed in detail.