Achieving high tensile strength-ductility synergy of a fully-lamellar structured near alpha titanium alloy at extra-low temperatures

The previous study has indicated that a near alpha titanium alloy of an equiaxed microstructure could hardly exhibit a desirable ductility at 20 K. This study aimed at achieving a promising balance of superhigh strength and excellent ductility of a Ti−3Al−3Mo−3Zr (wt%) alloy in cryogenic temperature field. Temperature dependence of tensile properties and deformation behavior was investigated systematically. It was found that the ultimate tensile strength (UTS) and elongation-to-fracture (EI) jumped from 730 MPa and 19.0% at 298 K to 1300 MPa and 23.0% at 77 K, respectively. Ultrahigh UTS up to 1600 MPa and an acceptable EI of 13.5% were achieved at 20 K. The ultrahigh UTS at 77 and 20 K was considered to be attributed to the sharp increase of CRSS of slip and the Hall-Petch effect of {101̅2}< 101̅1̅> twinning. The enhanced ductility at 77 K was owing to the improved strain hardening ability from large-scale twinning and prismatic and basal slips. Besides, a serrated plastic flow took place at 20 K, which was essentially because the intermittent start of twinning brought about alternate stress jump and cliff-like drop. A fully-lamellar microstructure is suggested to synchronously enhance the strength and ductility of a near-alpha titanium alloy at extra-low temperatures.