Simultaneous improvement in strength and ductility of CT20 titanium alloy at cryogenic temperature

Abstract

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of the CT20 alloy with a //ND texture were investigated. The CT20 alloy with equiaxed microstructure exhibits excellent mechanical properties with simultaneous increase in strength and elongation at cryogenic temperature. In current study, the initial //ND texture promotes basal slip actuation effectively and continuously increases Schmid factor (SF) of other slip systems to promote multiple slip. Cryogenic temperature weakens the deformation texture due to the promotion of multiple slip. Since the decrease of the stacking fault energy (SFE), more twins in number and variety nucleate at 77 K and promote multiple slip. It causes strong cryogenic twinning-induced plasticity (TWIP) effect. Grain refinement induces strong cryogenic dynamic Hall-Petch effect resulting in high strain-hardening rate (SHR) and strength. The yield strength (YS, ∼1052.67 MPa), ultimate tensile strength (UTS, ∼1102.51 MPa) and elongation (EL, ∼21.1 %) of the 77 K specimen are about 84.1 %, 69.1 % and 38.8 % higher than its counterpart at RT, respectively. In addition, cryogenic temperature changes the initiation location of cracks and promotes cracks initiation at grain boundaries homogeneously.

Keywords

• CT20 alloy
• Cryogenic temperature
• Tensile properties
• Twinning
• Deformation mechanisms