Laser powder bed fusion of titanium–oxygen–vanadium alloys: unraveling the non-monotonic ductility response phenomenon and strengthening mechanisms

Oxygen interstitial solid solution strengthening is a common method to enhance the strength of titanium alloys fabricated by laser powder bed melting (LPBF) process. However, the addition of oxygen often leads to a significant decrease in ductility, resulting in oxygen embrittlement. Adding β-phase-stabilized elements (such as Fe and V) can enhance the strength of LPBFed titanium alloys. In this study, a series of Ti-O-V alloys is fabricated using the LPBF process with (TiO₂ + V)/CP-Ti mixed powder. The synergistic effect between interstitial O solid solution strengthening and V substitution solid solution strengthening is investigated. With the increase in V content, the ultimate tensile strength increases from 853 MPa to 1165 MPa, while the elongation of the alloy shows a non-monotonic response. Multi-scale characterization reveals that the addition of V and O caused lattice distortion. Under the condition of adding 2 wt% V, a triangular α′ martensite variant appears, providing additional accommodation space for deformation and restoring the plasticity. The addition of V also leads to a dual-phase structure of α/β in the microstructure, generating a semi-coherent interface stress field that hinders dislocation. The improvement in strain hardening ability is attributed to the presence of high-density and necessary dislocations and dislocation walls at the α/β interface. This study provides a new paradigm for the preparation of in-situ titanium-based composites with high strength and high strain hardening capacity through LPBF.