Laser additive manufacturing of new α+β titanium alloy with high strength and ductility

Abstract

The capability to control volume fraction and morphology of α phase in α+β titanium alloys makes this group of alloys a suitable choice to develop new compositions to deal with the formidable requirement of industrial development. However, further alloying is challenged because of the difficulty of uniform mixing during the melting process and the severe segregation during solidification. Due to the intense convection within small melt pool, additive manufacturing (AM) can achieve uniform concentration distribution and thus is a perfect alloying strategy to exert the potential of more species of alloying elements. To fulfil the potential of alloying, an α+β titanium alloy with new composition was additively manufactured in this study by laser directed energy deposition (LDED). The as-deposited new α+β titanium alloy exhibited near equiaxed prior β grains and intragranular ultrafine basket-weave microstructure in which the thickness of α lath is 0.4 ± 0.1 μm. A fibrous root morphology of primary α (αp) whose thickness is 1.4 ± 0.2 μm formed by macroscopic diffusion in the subsequent annealing process and this special morphology is the main reason of the improvement of ductility. With the aid of this special morphology and the nucleation of fine secondary α (αs), the ultimate tensile strength (UTS) and ductility can reach 1247±3 MPa and 9.2 ± 0.2%. The achievement of high strength and good ductility indicates that the development of new titanium alloys is suitable for AM and thus could be the future direction for titanium alloys research.