Strength and ductility optimization of laser additive manufactured metastable β titanium alloy by tuning α phase by post heat treatment

Abstract

The metastable β titanium alloy Ti–5Mo–5V–8Cr–3Al (TB2) was fabricated by laser melting deposition (LMD). α phase was tuned by post heat treatment (PHT) in order to obtain a good combination of strength and ductility of laser melting deposited (LMDed) TB2 alloy. This study demonstrated that TB2 alloy exhibited fully equiaxed β phase after LMD, which possessed good ductility (≈18.2%) with ultimate tensile strength (σUTS) of 811 MPa. The β solution plus aging treatments resulted in higher strength (σUTS ≈ 1136–1312 MPa) in comparison with the (α+β) solution plus aging treatments (σUTS ≈ 1037 MPa) because of higher-density acicular α phase with finer size (width∼200 nm). Two-step aging resulted in improved ductility (≈9.8–12.9%) in comparison with the one-step aging (≈2.0%) due to coarsening of α phase. Finally, β solution plus two-step aging was proved to be appropriate for LMDed TB2 alloy to achieve a good combination of strength (σUTS ≈ 1136 MPa) and ductility (≈9.8%).