Revealing hot deformation behavior and optimizing process parameters of as-cast Ti–5Al–5Mo–5V–1Cr–1Fe alloy

Abstract

Hot compression tests are carried out at temperatures ranging from 900 °C to 1050 °C, strain rates ranging from 0.001s−1 to 1s−1 and deformation degree ranging from 60% to 70% on the Gleeble-3500 thermal simulator. Strain-compensated Arrhenius constitutive model, activation energy maps, hot processing maps and microstructure evolution are used to analyse the flow behavior of as-cast Ti-55511 alloy. At low temperature (≤950 °C), the flow softening behavior is mainly related to cracks, deformation bands (DBs) and DRV at high temperature (≥1000 °C) and high strain rate (≥0.1s−1), and DRV at high temperature (≥1000 °C) and low strain rate (≤0.01s−1). DBs and cracks are the main forms of hot deformation instability. There is a competitive relationship between DRV and DBs. Under high strain rate (≥0.1s−1), DBs are more likely to occur. Under low strain rate (<0.1s−1), the DBs are restrained by DRV. The simultaneous activation of different slip systems causes the rotation of different areas in the grains to form DBs. The DRX grains in the DBs are produced by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX), but the DRX grains in the sample without DBs are produced by CDRX. The analysis of hot activation energy (Q), strain rate sensitivity index (m), power dissipation efficiency (η), flow instability parameter (ξ(ε˙)) and microstructure analysis showed that 1000°C–1050 °C/0.001s−1–0.01s−1 are an optional processing window. And the proportion of recrystallization is the highest at strain of 1.2 and 1000 °C/0.01s−1, so it can be considered as the optimal processing parameter.