Effect of hot working on flow behavior of Ti–6Al–4V alloy in single phase and two phase regions

Hot deformation behavior of the alloy Ti–6Al–4V was investigated via conducting hot compression tests at temperatures of 800–1150 °C and at strain rates, ranging from 0.001 s⁻¹ to 1 s⁻¹, at an interval of an order of magnitude. The apparent differences of flow stress curves obtained in dual phase α + β and single phase β regions were analyzed in term of different dependence of flow stress to temperature and strain rate and different microstructural evolutions. The values of strain rate sensitivity and apparent activation energy were obtained respectively as 0.20 and 530 kJ/mol for two phase microstructure. However, for single phase β microstructure they were approximated as 0.19 and 376 kJ/mol, respectively. It was found that in two phase region the values of strains corresponding to peak point, ε_p, and the highest rate of flow softening, ε^*, are almost independent to Zenner–Hollomon parameter. In single phase region, ε_p and ε^* exhibited a direct relationship to Z parameter and the corresponding empirical equations were proposed.