High-temperature deformation behavior of as-cast TC21 titanium alloy

Isothennal compression tests of as-cast TC21 titanium alloy are conducted in the deformation temperature ranging from 1000°C to 1150°C with an interval of 50°C. strain rate ranging from 0.01s^-1 to 10.0s ^-1 and height reduction of 60% on a computer controlled Gleeble 3500 simulator. The true stress-strain curves under different deformation conditions are obtained. Based on the experimental data, the hot deformation behavior of as-cast TC21 alloy is explored. A processing map of the isothermally compressed TC21 alloy is constructed at a strain of 0.5. The deformation mechanisms of the alloy in the whole regimes were investigated through the microstructure observation. It is found that the softening phenomena of stress-strain curves at high strain rate (>1s^-1) is mainly associated with flow localization, which is caused by local temperature rise, whereas at low strain rate, the softening phenomenon is associated with dynamic recovery and recrystallization. In addition, the stress-strain curves exhibit a discontinuous yielding phenomenon that is attributed to the generation of mobile dislocation from the grain boundaries, and the serrate oscillation phenomenon was an indication of flow localization.