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

Abstract

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\xa0MPa at 77\xa0K and 1725\xa0MPa at 20\xa0K 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\xa0K, but sharply drops down to 4.5% at 20\xa0K. Because of the dynamic Hall-Patch effect induced by the extensive {332} 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\xa0K. In contrast to the stable deformation at 298\xa0K and 77\xa0K, a serrated deformation (i.e. discontinuous plastic flow) takes place at 20\xa0K. 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\xa0K.