The microstructure evolution in the isothermal compression of Ti-17 alloy

The effects of processing parameters on flow curves and microstructure evolution in the isothermal compression of Ti-17 alloy are investigated. The experiments are conducted in a deformation temperature range of 800-920°C, strain rate range of 0.01-10.0s^-1 and height reduction range of 30-70%. The flow stress increases with a decrease in deformation temperature or an increase in strain rate. Based on the optical microstructure observations, both of deformation temperature and strain rate have a great effect on the volume fraction of α grains. The effect of strain rate on primary α grains morphology and softening mechanism is of first-order importance compared with the effects of deformation temperature and strain. Transmission electron microscope (TEM) analysis is carried out at a deformation temperature of 840°C, strain rate of 0.1s^-1 and 10.0s^-1 to reveal the two mechanisms for the morphology evolution of primary α grains. When the strain rate is relatively low, the primary α grains are globularized after the penetration of β phase along α/α subboundaries. While the strain rate is relatively high, the primary α grains are elongated, and the dislocation density in grain interior is relatively high.