Surface deformation behavior of beta solution treated and overaged Ti-6Al-4V during laser shock processing

The surface of a beta solution treated and overaged Ti-6Al-4V alloy specimen deformed by laser shock processing was studied using electron backscatter diffraction, scanning electron microscopy, and atomic force microscopy. Slip steps were observed within grains oriented with their c axis nearly parallel to the specimen surface normal. Based on the slip step traces and orientation information, the slip planes were determined to be { 11 2 ¯ 2 } for grains with their c axis within 15° of the specimen surface normal and { 11 2 ¯ 1 } for grains with their c axis between 15° and 40° away from the specimen surface normal. Although both these planes are known to belong to twinning systems, { 11 2 ¯ 2 } ⟨ 11 2 ¯ 3 ¯ ⟩ and { 11 2 ¯ 1 } ⟨ 11 2 ¯ 6 ¯ ⟩ , respectively, the latter has not been observed to operate as a slip system. Examination of the Taylor factors associated with these slip systems shows that the grains with slip steps have the lowest Taylor factors. Determination of localized lattice rotations showed a unique behavior in grains with slip steps, such that all the lattice rotations were concentrated about the steps, with almost no orientation variations in between slip steps. This distribution indicates that stress concentrations exist at the slip steps, which could potentially affect the performance of the material.