A high strength and low modulus metastable β Ti-12Mo-6Zr-2Fe alloy fabricated by laser powder bed fusion in-situ alloying

Abstract

Biocompatible β Ti-alloys with high strength and low modulus are of interest for additive manufacturing of biomedical implants. In this study, a metastable β Ti-12Mo-6Zr-2Fe (TMZF) alloy with highly dense structure was successfully fabricated by laser powder bed fusion (LPBF) from low-cost elemental powders. The applied different scanning strategies (simple and chess scan), and post heat treatment can regulate both the texture and secondary phases. The formation of strong {100}< 001 > texture leads to the low elastic modulus of TMZF alloys, while nano-sized α" phases induce significantly strengthening effect. The as-fabricated TMZF alloy via simple scanning strategy shows considerably high strength due to the high density of α", ω phases and sessile dislocations, but it is brittle owing to the presence of ω phase. The TMZF alloy, manufactured using chess scanning strategy, possessed high yield strength of 1,026 MPa, low modulus of 85.7 GPa and good ductility of 12.7%. This results from its unique hierarchical microstructure containing α" phases, heterogeneous grains and the formation of {100}< 001 > texture. After solution heat treatment, the specimens exhibit stronger {100} < 001 > texture, hence lower modulus of 70.9 GPa. High yield strength of 943 MPa was maintained due to the formation of plate-like α" precipitates. The TMZF alloy fabricated by in-situ alloying based LPBF demonstrates comparable strength to that of Ti-6Al-4V alloy, but much lower elastic modulus, suggesting that it could be a potential candidate for some implant applications.