摘要： A hot-rolled Tie6Ale4V (Ti-64) sheet was surface-treated by pulsed laser at two different powers (100 and 200 W), with microstructural features and hardness before and after the laser surface treatment (LST) systematically investigated. Results show that after the LST at both powers there are two modi?cation zones with distinct microstructural characteristics: melted zone (MZ) near the laser beam center, completely composed of ?ne martensitic plates with dense {10e11} nanotwins inside them; heat-affected zone (HAZ) far away from the laser beam center, comprised of mixed structures of short-rod b particles, martensitic plates and untransformed bulk a grains. Hardness measurements reveal that the hardness of the Ti-64 sheet can be markedly increased (especially in the MZ) after the LST. In-depth analyses suggest that the hardness increase in the MZ can be ascribed to combined contributions from grain re?nement, presence of nanotwins and solid solution of alloying elements, while only the structural re?nement by ?ne plate structures contributes to hardening in the HAZ. Comparisons between both the LSTed specimens reveal that increasing the laser power from 100 W to 200 W can effectively enlarge the laser-modi?ed zones (both the MZ and the HAZ) and simultaneously re?ne plate structures, leading to further hardness increase.