Cryogenic tensile properties and deformation behavior of a superhigh strength metastable beta titanium alloy Ti–15Mo–2Al

Abstract

Considering the great potential of extremely-low temperature applications, cryogenic tensile properties and deformation behavior of a metastable β-Ti alloy Ti–15Mo–2Al were investigated. Superhigh ultimate tensile strength ( UTS ) of 1535 MPa at 77 K and 1725 MPa at 20 K are achieved. The elongation-to-fracture ( EI ) of the alloy is found to be maintained at a high level up to 22.0% at 77 K, but sharply drops down to 4.5% at 20 K. Because of the dynamic Hall-Patch effect induced by the extensive {332}<113> twins formed during deformation and the strong back-stress strengthening at twin boundaries, the work hardening rate and tensile strength are significantly enhanced at 77 K. In contrast to the stable deformation at 298 K and 77 K, a serrated deformation (i.e. discontinuous plastic flow) takes place at 20 K. The related cryogenic deformation mechanism and fracture behavior are illustrated from the dynamics of dislocation pileups and thermophysical activation aspect. It is proposed that cryogenic applications of the metastable β-Ti alloy are practically feasible at least at temperatures not lower than 77 K. • High-purity metastable β-Ti alloy has superhigh tensile strength at 77 and 20 K. • Ti–15Mo–2Al alloy maintains satisfying tensile ductility up to 22.0% until 77 K. • {332}<113> twins result in continuous hardening and superhigh cryogenic strength. • Discontinuous plastic flow takes place and results in much low ductility at 20 K. • Serrated deformation is caused by intermittent activation of dislocations and twins.