A Two-Stage Constitutive Model for Ti2AlNb Alloy Based on Asymptote Approach and Temperature-Corrected Stress

Abstract

The flow behavior of Ti2AlNb-based alloy is critical to the research of hot forming due to its high sensitivity to the temperature and strain rate. The hot compression tests were conducted by using a Gleeble thermo-mechanical simulator in the temperature range of 950-1080 °C with strain rate from 0.001 to 10 s−1. The flow curves were modified firstly by taking into account the interface friction. In order to neutralize the thermal effect caused by high-speed deformation, the influence of strain rate on the deformation-induced temperature rise was evaluated, and the true temperature was obtained based on the collected stress–strain data. It was found that, under certain strain and strain rate, the true stress varied with the true temperature in an ‘inverted S’ format. Therefore, an ‘inverted S’ relation was adopted to calculate the flow stress at the given temperature. After the correction of flow stress, the constitutive model including the parabolic equation and modified Arrhenius equation in asymptotic form was established, and the discontinuous yielding and normal yielding behaviors were depicted, respectively. The constitutive model was integrated into the software DEFORM, by which the accuracy and predictability were verified.