Flow behavior and deformation mechanism in the isothermal compression of the TC8 titanium alloy

The TC8 titanium alloy was isothermally compressed at the deformation temperatures ranging from 820°C to 980°C, strain rates of 10s^-1, 30s^-1 and 50s^-1, and a height reduction of 60%. An optical microscope (OM) and a transmission electron microscope (TEM) were used to examine the microstructure. The flow stress decreases with the increasing of deformation temperature and decreasing of strain rate. The strain rate sensitivity exponent m increases gradually to a maximum value as the deformation temperature increases from 820°C to 940°C, and then decreases at the deformation temperature of 980°C. The strain hardening exponent n decreases with the decreasing of deformation temperature, and gets a maximum value at the strain rate of 30s^-1 and a given deformation temperature. According to the microstructure examination, the variation of flow stress, m and n values are found to depend on the phase transformation, grain morphology, dislocation content, dynamic recovery (DRV) and dynamic recrystallization (DRX) of primary α and β phases. The apparent activation energy for deformation is 429.766±80.394-383.478±78.734kJmol^-1, and indicates that the dislocation climbing is not the main deformation mechanism. This deduction agrees well with the microstructure examination which shows that the DRX of primary α phase and β phase play an important role in the isothermal compression of TC8 titanium alloy.