Laser powder bed fusion of metastable β titanium alloys: enhanced strength and plasticity through simultaneous activation of multiple deformation mechanisms

Abstract

The excellent mechanical properties of metastable β titanium alloys make them suitable for use in aerospace and biomedical fields. However, the deformation mechanisms of these alloys are currently limited to slip/twinning or twinning/transformation-induced plasticity (TRIP) based on β phase stability, hindering high strength and plasticity. In this study, we regulated the laser powder bed fusion (LPBF) parameters to control ω phase density and β phase stability, thereby simultaneously triggering slip/twinning/TRIP deformation mechanisms and resulting in a high strength-plastic metastable β titanium alloy. The results demonstrated that reducing laser energy density decreased the ω phase fraction, leading to a decrease in β phase stability. The formation of the ω phase in specimens with low energy density increased the strain requirements for TRIP to occur, promoting dislocation slip and twinning initiation under low strain conditions. Due to TRIP effect activation at high strains, the α′ phase rather than the α″ phase became the transformation product, subsequently promoting twin formation within the α′ phase during further deformation. Generation of dislocation/twinning/TRIP and twins in the α’ phase resulted in an LPBF-ed metastable β Ti1023 alloy with excellent strength and plasticity, which surpassed previous research findings for LPBF metastable β titanium alloys and overcame the strength-plasticity trade-off observed in traditional metal materials.