Constitutive modelling, dynamic globularization behavior and processing map for Ti-6Cr-5Mo-5V-4Al alloy during hot deformation

Abstract

Hot compression tests of Ti-6Cr-5Mo-5V-4Al alloy were carried out under the temperature range of 963–1113 K and strain rates of 0.001, 0.01, 0.1, 1 s−1 on a Gleeble-3500 isothermal simulator. The strain compensated Arrhenius model (SCAM) was developed after calculating the material constants including α, lnA, n and Q. Also, genetic algorithm (GA) was applied to optimize the material constants according to the acquired material constant ranges and the GA optimized Arrhenius model (GAOAM) was constructed for flow stress prediction. The prediction capabilities of the two models were assessed by correlation coefficient (R) and average absolute relative error (AARE). The results showed that GAOAM was better than SCAM in prediction precise. Two dynamic globularization mechanisms were proposed to describe the dynamic globularization behavior at different strain rate conditions according to the SEM observations. Extrusion type globularization (ETG) occurred at lower strain rate condition and cutting type globularization (CTG) occurred at higher strain rate condition. Also, dynamic globularization occurred easier at lower temperature and the α grain was squashed but not spherized at higher temperature. The processing map based on dynamic materials model was constructed for the microstructure identification. The instability region occurred at the area with high strain rate and low temperature and high η-value region was at the area with low strain rate and high temperature. According to the OM microstructure observations, flow localization occurred at the instability region and the dynamic recrystallization of β grain occurred at the high η-value region. Thus, the microstructure identification ability of the processing map was verified and this processing map could be referred to in the actual production.