Abstract:The microstructure evolution and deformation mechanism at room temperature and cryogenic temperature of cryogenic titanium alloy bars were investigated through controlling Mo equivalent. The results show that with the increase in Mo equivalent, β phase stability is improved, which limits the precipitation of α phase. High-Mo-equivalent alloy forms single-phase β grains without α phase precipitation. As for the low-Mo- equivalent alloy, the basketweave microstructure occurs. At room temperature, the plasticity of stable β alloy Ti-38V is higher, which is attributed to bcc-β phase possessing more slip systems than hcp-α phase. The slip ability of β phase is better than α phase, leading to the excellent plastic deformation ability of β phase. As a result, a large number of dimples occur in the tensile fracture. The strength of (α+β) alloy Ti-3Al-6Mo is higher, which is mainly caused by the strengthening effect of interweaved α lamella. The higher Schmid factor of the (α+β) titanium alloy makes the dislocation slip easier, which makes the dislocation slip act as the primary deformation mechanism at both room and cryogenic temperatures, while deformation twins can also be activated at cryogenic temperature. For the stable β titanium alloy, stress concentration occurs at the grain boundary because of dislocation pile-up. The higher V content increases β stability, which makes the fracture sample at cryogenic temperature without stress-induced mechanical twins. Consequently, the deformation ability is poor and it exhibits brittle fracture characteristics at cryogenic temperature.