Natural aging of a metastable β-type titanium alloy to simultaneously enhance yield strength and uniform elongation

Abstract

Natural aging has received little attention in Ti alloys. In the present study, natural aging was detected in a transformation-induced plasticity (TRIP) Ti-15Nb-5Zr-4Sn-1Fe alloy which resulted in a significant increase in the yield strength from 493 MPa to 683 MPa without sacrificing ductility. Natural aging resulted in diffusional coarsening of the ω particles, which decreased the ω-to-β reversibility and impeded the stress-induced β-to-αʹ martensitic transformation under subsequent deformation. Consequently, the stress-induced β-to-αʹ martensitic transformation occurred continuously over a wider range of strains than without natural aging. This led to simultaneous increases in the yield strength and uniform elongation, attributing to enhanced strengthening from the coarsened ω and the more sluggish stress-induced martensitic transformation. These findings demonstrate the potential to regulate stress-induced martensitic transformation and mechanical properties of metastable β-Ti alloys by controlling the development of ω through natural aging.