Hot Deformation Behavior of Ti-6Al-4V-0.5Ni-0.5Nb Titanium Alloy

Characterization of hot deformation behavior of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy was investigated through isothermal compression at various temperatures from 750 to 1 050 °C and strain rate from 0.01 to 10 s⁻¹. The isothermal compression experiment results showed that the peak stress of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy decreased with the temperature increasing and the strain rate decreasing. The softening mechanism was dynamic recovery below T_β and changed to dynamic recrystallization above T_β. The arrhenius-type relationship was used to calculate the constitutive equation of Ti-6Al-4V-0.5Ni-0.5Nb alloy in two-phase regions. It was found that the apparent activation energies were 427.095 kJ·mol⁻¹ in the α+β phase region and 205.451 kJ·mol⁻¹ in the β phase region, respectively. On the basis of dynamic materials model, the processing map is generated, which shows that the highest peak efficiency of power dissipation of 56% occurs at about 1 050 °C/0.01 s⁻¹. It can be found in the processing maps that the strain had significant effect on the peak region of power dissipation efficiency of Ti-6Al-4V-0.5Ni-0.5Nb alloy. Furthermore, optimized hot working regions were investigated and validated through microstructure observation. The optimum thermo mechanical process condition for hot working of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy was suggested to be in the temperature range of 950–1 000 °C with a strain rate of 0.01–0.1 s⁻¹.