| Abstract: | Isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 °C in 50 °C intervals with a strain rate of 0.001–1.000 s?1. The high-temperature deformation behavior of the Ti555211 alloy was characterized by analysis of stress–strain behavior, kinetics and processing maps. A constitutive equation was formulated to describe the flow stress as a function of deformation temperature and strain rate, and the calculated apparent activation energies are found to be 454.50 and 207.52 kJ·mol?1 in the α + β-phase and β-phase regions, respectively. A processing map based on the Murty instability criterion was developed at a strain of 0.7. The maps exhibit two domains of peak efficiency from 750 to 950 °C. A ~60 % peak efficiency occurs at 800–850 °C/0.001–0.010 s?1. The other peak efficiency of ~60 % occurs at ≥950 °C/0.001–0.010 s?1, which can be considered to be the optimum condition for high-temperature working of this alloy. However, at strain rates of higher than 1.000 s?1 and deformation temperatures of 750 and 950 °C, clear process flow lines and bands of flow localization occur in the high-temperature deformation process, which should be avoided in Ti555211 alloy hot processing. The mechanism in stability domain and instability domain was also discussed. |
