Achieving strength-ductility synergy in laser-manufactured titanium alloys: a wire-powder synchronous feeding strategy with O-Fe microalloying

This study overcomes the long-standing strength-ductility trade-off in titanium alloy welding and additive manufacturing by introducing a novel laser-manufactured wire-powder synchronous feeding strategy incorporating oxygen-iron (O-Fe) microalloying. Through controlled experiments and multiscale characterization, the mechanism by which trace O-Fe additions regulate weld microstructure and mechanical properties is elucidated. The results show that O-Fe microalloying particles modify the growth conditions of acicular α/α′, reducing its aspect ratio and alleviating stress concentration at α/β phase boundaries. The microalloying elements substantially refine the grains during solidification through solute redistribution and a pronounced increase in undercooling. Quantitative analyses demonstrate that O-Fe microalloying reduces columnar grain width by 64.8%, modifies the aspect ratio of acicular α/α′ through solute redistribution with a 20.3% increase in minor axis and a 40.4% decrease in major axis, and achieves 63.9% grain refinement through elevated α/β interfacial energy and promoted heterogeneous nucleation. The optimized Ti-6Al-4V-0.5O-2.3Fe alloy exhibits exceptional mechanical performance, with a tensile strength of 1,266.6 MPa representing a 41.3% improvement and an elongation of 15.5% indicating an 80.2% enhancement, demonstrating great potential for high-performance industrial applications.