Coupling effect of loading mode and temperature on the deformation behaviors of TWIP β Ti alloy: From superior tensile strength-ductility synergy to low Charpy impact toughness

The Ti-8.5Cr-1.5Sn β Ti alloy with twinning induced plasticity (TWIP) effect was selected for the quasi-static tensile and Charpy impact tests at 298 K and 77 K to determine whether the strengthening and toughening strategy by TWIP effect can be extended to the cryogenic temperature. As the impact deformation temperature decreased from 298 K to 77 K, the Charpy impact toughness decreased obviously, even though a superior strength-ductility synergy was obtained under quasi-static tensile deformation at 77 K. Because the inhibition of deformation twins (DTs) activity under Charpy impact deformation at 77 K, together with the premature cracking along the formed twin boundaries (TBs), the density and width of the activated {332} DTs were significantly reduced. Meanwhile, the secondary DTs and {5811} DTs also were restrained due to the width of primary DTs was too narrow. The above influencing factors resulted in the size of plastic deformation region at crack tip at 77 K was obviously smaller than that at 298 K. The crack preferentially initiated and propagated along primary TBs, and finally a low Charpy impact absorbed energy was displayed at 77 K.