Strength-ductility improvement achieved by introducing heterostructured martensite in a Ti-6Al-4 V alloy

A novel strategy using laser surface remelting to produce hererostructured martensite structures for titanium alloy is proposed and verified in the current work. Such surface treated Ti-6Al-4 V specimens possess an excellent combination of strength and ductility compared to homogeneous materials. Dedicated microstructural observations indicated that the martensite laths with sizes increasing from surface to interior were eventually developed after laser surface remelting. The remelting surface region consisted of parallel coarse martensite laths, fine martensite laths with scattered orientations and 101¯1 twins. Moreover, the dislocations with Burgers vector of 1/3112¯0 piled up at the front of 101¯1 twins boundaries inside martensite laths were identified unambiguously after tension deformation. Accordingly, the possible mechanisms responsible for the synergy of strength and ductility were proposed and discussed. The current results would open a possibility for obtaining Ti-6Al-4 V with high strength and ductility synergistically, and this strategy may also be applicable to other materials.