Microstructure evolution and strengthening mechanisms of pure titanium with nano-structured surface obtained by high energy shot peening

In this study, the microstructure evolution and strengthening mechanisms of pure titanium processed by high energy shot peening (HESP) have been studied. The results show that the deformation layer is formed on the surface and the microstructure exhibits with the equiaxed 20-40 μm grains in the matrix after HESP. A nanocrystal surface layer is produced by means of HESP on pure titanium. The formation of nano-grains on the surface can be separated into four steps: (1) the formation of the dislocations tangles; (2) the occurrence of the intersection of twins; (3) the appearance of slip band and subgrains; (4) the formation of uniformly distributed nanometer-scale grains. With increasing the holding time, the strength increases and the elongation decreases due to the work hardening effect and the formation of the nanocrystals on the surface.