Laser shock peening of laser additive manufactured Ti6Al4V titanium alloy

Laser shock peening is combined with laser additive manufacturing to modify the surface microstructures and mechanical properties of as manufactured Ti6Al4V titanium alloy. Microstructural evolution, microhardness distribution, residual stress distribution and mechanical properties are examined before and after LSP. After peening, the interplanar spacing of lattices of both alpha and beta phases decreases without any new phase formation. Grain refinement is achieved with average grain size of alpha phase decreasing from 33.6 to 24.3 mu m. High density of dislocation lines, tangles, and multi-directional mechanical twins are observed. Residual stress is turned from tensile to compressive state with an affected depth of around 700 mu m. The hardening layer reveled by micro-hardness is around 900 mu m in depth. Grain refinement accounts for the yield strength, ultimate tensile strength, and elongation enhancements after peening.