Microstructural and Mechanical Characterizations of a Ductile Metastable β Titanium Alloy Subjected to Low Temperature Annealing

Low temperature thermal treatments, between 423K and 573K, were performed to optimize the mechanical properties of a ductile beta metastable titanium alloy with TRIP and TWIP effects. A set of short-time heat-treatments (STT) were applied at 423K, 473K, 523K, and 573K for 60 and 600s, respectively. The results show that the tensile strength and Vickers hardness increase as the annealing temperature increasing. The sample annealed at 423K for 60s possessed a modest yielding strength (≈566MPa), Vickers hardness (≈327HV) and excellent elongation (≈53%); whereas the sample annealed at 573K for 600s shows a very high yielding strength (≈1256MPa), Vickers hardness (≈441HV) but a small ductility. It is worth noting that the sample annealed at 473K for 60s exhibited the best combination of high strength (close to 1200MPa of true stress) and a stable plastic zone of ɛ=0.4(true strain) with a significant strain hardening effect. It is clarified that both TRIP and TWIP deformation mechanisms are promoted after the heat treatment of 60s at 473K, resulting in good balance among the tensile strength, the ductility and the strain hardening behavior.