Grain boundary recrystallization and novel dislocation patterns on Ti-6Al-4V surface induced by high-repetition ultrashort-pulse laser peening.

Ultrashort-pulse laser peening has garnered increasing attention in recent years; however, the underlying mechanisms of microstructural evolution in metal matrices under ultrafast shockwaves remain poorly understood. Here, we investigate the transformation of micro- and nanoscale structures on the Ti-6Al-4V surface induced by high-repetition ultrashort-pulse laser peening. Our results demonstrate that ultrashort-pulse laser peening induces significant dynamic recrystallization at grain boundaries, along with the formation of a variety of dislocation patterns within the grains. The recrystallization is attributed to the severe misorientation accumulation at the grain boundaries during the repetitive impact process, which leads to the formation of ribbon-like grains aligned along the original boundaries. Interestingly, within the diverse dislocation nanostructures, we identified a novel fish-scale dislocation architecture, a feature not previously reported in the literature. The formation of these unique nanostructures is attributed to the distinctive high-repetition, high-strain-rate characteristics of ultrafast shockwaves induced by ultrashort-pulse laser peening. This study advances our understanding of high-frequency ultrafast shock dynamics, offering new insights into the design and fabrication of high-performance metallic materials.