Enhancing elastic admissible strain via oxygen alloying in LPBF-fabricated metastable titanium alloys: microstructure evolution and mechanical properties

Developing titanium alloys with high elastic admissible strain (EAS) is crucial for biomedical applications. In this study, a series of Ti-14Nb-6Zr-3Fe-xO (TNZF-xO, x = 0.20, 0.35, 0.50, 0.65 wt%) metastable β titanium alloys were fabricated via laser powder bed fusion to investigate the role of oxygen in tailoring microstructure and resulting mechanical properties. Microstructural analysis revealed that oxygen addition induced spinodal decomposition of the β matrix into β′ phases and promoted the precipitation of the ω phase. A slight refinement in grain size, from 30.5 μm to 28.1 μm, was observed with increasing oxygen content. Mechanical testing demonstrated that higher oxygen levels led to a continuous increase in yield strength (from 1147 MPa to 1288 MPa) and hardness (from 4.06 GPa to 4.58 GPa). This strengthening is primarily attributed to the ω phase and solid solution strengthening, while the β′ phase contributes to work hardening during deformation. The elastic modulus exhibited a non-monotonic trend, initially decreasing and then increasing, which is attributed to the competing effects of β-phase destabilization and ω-phase stiffening. The TNZF-0.65O alloy demonstrated a yield strength of 1288 MPa, an elastic modulus of 70 GPa, an elongation of 5.6%, and an exceptional EAS of 1.84.