Achieving a high strength and tensile ductility synergy of a high-oxygen powder metallurgy near alpha titanium alloy by importing βt domains into lamellar structures

Abstract

A near alpha titanium alloy Ti−3Al−2Zr−2Mo (wt%) was prepared by vacuum sintering of TiH2-based powder compact and multiple directional hot forging. β-transformed (βt) domains were imported into lamellar structures in order to break the strength-ductility trade-off dilemma of high-oxygen PM titanium alloys. It was revealed that βt domains were harder than α laths in bi-lamellar microstructure prepared by annealing at 880 °C, and the α/βt interfaces contributed to activation of abundant basal and non-basal slip systems in α laths, which brought about strong strain hardening and resulted in simultaneously enhanced strength and ductility. The bi-lamellar microstructure renders a high ultimate tensile strength (UTS) of 881 MPa and an elongation-to-fracture (EI) of 15.0%. By contrast, basket-weave microstructure produced via annealing at 950 °C exhibited the highest UTS up to 975 MPa, mainly because that its predominant α laths become inversely harder than adjacent βt domains. Correspondingly, strain hardening got much weakened, stress concentration at colony boundaries led to a premature fracture and a low ductility. A new insight of βt domains and their effect on mechanical properties of PM near alpha titanium alloy is proposed.