Plastic deformation behavior of titanium alloy by warm laser shock peening: Microstructure evolution and mechanical properties

The plastic deformation behavior of Ti6Al4V titanium alloy subjected to 300 degrees C-warm laser shock peening (WLSP) was inferred from its microstructure evolution and mechanical properties. Through dynamic strain aging (DSA), WLSP achieved higher dense dislocations than room temperature laser shock peening (LSP). In addition, significant {101(-)2} deformation twinning activity was observed after WLSP. Twinning activity at such an ul- trahigh strain rate and high temperature is a first-time observation in titanium alloy, and was attributed to an enhanced dislocation dissociation mechanism during WLSP. Moreover, an amorphization layer was generated on the top surface of the WLSP-processed sample, but not on the LSP-processed sample. This amorphization was effected by the increased free energy provided by the multiplying dislocations and deformation twins, combined with the reduced energy barrier of the crystal-to-amorphous transformation at high temperature. Relative to LSP, WLSP increased the width and depth of the compressive residual stress in the titanium alloy by 36.2% and 21.8% respectively, and improved the surface micmhardness by 5%. The latter enhancement was conferred by the increased density of dislocations and deformation twins. Overall, WLSP improved the mechanical properties of the titanium alloy.