Effect of Phase Transformation on High Temperature Dynamic Flow Stresses of CP-Ti

Abstract

The dynamic mechanical flow stresses of titanium alloys at high temperatures can be strongly affected by phase transformation. Literature documents the flow stresses of the commercial alloy CP-Ti only up to 750 °C. In this study, we investigated the response of commercial alloy, CP-Ti, at very high temperatures of up to 1200 °C while under dynamic loading at strain rates between 1800 and 3500 s⁻¹. Our low temperature data shows good agreement with previous studies, including the dynamic strain aging behavior the material is known to show. For the strain rates in our study, we observe a dynamic strain aging (DSA) peak at around 250 °C, where the thermal softening behavior is milder. The flow curves in the DSA zone are also characterized by a spike in the work hardening of the material. At very high temperatures, we discover a noticeable shift in the softening behavior coinciding with the allotropic transition point at around 880 °C. The data suggests that at this transition point, there is a sharp drop in the flow stresses. The rates of thermal softening are also distinctly different prior and after the transition. Future material models which cover high temperature constitutive response have to consider this effect of phase transformation on the dynamic flow stresses as well.