Strain‐induced gradient crystalline evolution mechanism of Ti‐6.5Al‐3.5Mo‐1.5Zr‐0.3Si during ultrasonic impacting and rolling process

This study investigates the gradient crystalline evolution mechanism of titanium alloy Ti‐6.5Al‐3.5Mo‐1.5Zr‐0.3Si during ultrasonic impacting and rolling process (UIRP). Microscopic observations indicated that dislocation movement is quite active at the early stage of plastic deformation, but twinning soon dominates the plastic deformation in the following long period of time. The very high energy density provided by the UIRP generates a surprisingly large number of epitaxy stacking faults despite the high energy they require. The actual atomic layers present a topological structure, facilitating the conversion between intrinsic stacking faults and epitaxy stacking faults, promoting the generation of twins, partial dislocations, and their intersection. After grains are refined to nano‐scale, dislocation slip again becomes the main deformation mode. In addition, beamlike secondary α ‐phase and laminar secondary α ‐phase were observed precipitating in β ‐substrate. These secondary α ‐phases could reduce the dislocation slip resistance and improve the elongation, thus contributing to improve the plasticity of alloy.