The strain rate sensitivity exponent and the strain hardening exponent of as-cast TC21 titanium alloy in β single-phase region

Abstract

The thermal deformation behavior of as-cast TC21 titanium alloy during hot compression in β single-phase was studied. The deformation temperature ranging is 1273 K to 1473 K (temperature interval is 50 K), the strain rate is 0.1 s−1,1.0 s−1and10 s−1, and the height reduction is 30%, 45% and 60%, respectively. The effect of deformation parameters on flow stress, strain rate sensitivity exponent and strain hardening exponent is analyzed. The flow stress of as-cast TC21 alloy has a steady-state characteristic with the change of deformation parameters. As the temperature increasing, the strain rate sensitivity exponent curves appear as cosine or sinus with the increasing strain rates from 0.1 s−1 to 10 s−1, respectively. Two curves of the strain hardening exponent at strain rates of 0.1 s−1 and 1 s−1 change lightly as the increasing deformation temperature. However, while the strain hardening exponent curve at strain rate of 10 s−1 decreases as the increasing deformation temperature, and because of the different effects of dynamic recrystallization on the hardening mechanism and softening mechanism. In addition, it is found that under the condition of strain rate of 10 s−1 and temperature range of 1273 K−1473 K, when the strain exceeds the critical strain of 0.5–0.55, the strain rate sensitivity exponent and strain hardening exponent will change greatly.