Abstract: The hot deformation behaviors of a new type of metastable β-titanium alloy Ti-1500 were studied through isothermal compression tests at 750-910 ℃ with 0.001-10 s^-1. The hyperbolic sine Arrhenius constitutive equation of coupled strain was established. Based on the dynamic material model and Prasad's rheological instability criterion, the hot working diagrams were constructed, and the microstructure after deformation was analyzed. The results show that the flow stress of the alloy decreases as the deformation temperature increases and the strain rate decreases. Under the same conditions, the peak flow stress of the alloy is slightly higher than that of the Ti55531 alloy, but lower than that of the M28 alloy. The average thermal deformation activation energy of the alloy in the two-phase region is 291.36 kJ/mol, which is much higher than the self-diffusion activation energy of pure titanium. The activation energy in the β single-phase region is 153.96 kJ/mol, which is close to the self-diffusion activation energy of pure titanium. The peak value of energy dissipation efficiency in the two-phase region is located at a low strain rate (0.001 s^-1), while the peak value of energy dissipation efficiency in the single-phase region lies in the middle and low strain rates (0.01-0.1 s^-1). At all test temperatures, deformation instability occurs when the strain rate is higher than 1 s^-1. Combined with microstructure analysis, deformation can be divided into three regions, namely low temperature and low strain rate β→α phase transition zone, medium to high temperature and low strain rate β recrystallization zone and unstable region with uneven deformation at high strain rates.

Key words: metastable β-titanium alloy Ti-1500, hot deformation, constitutive equations, hot processing maps, dynamic recovery, discontinuous dynamic recrystallization