Multi-stage hot deformation and dynamic recrystallization behavior of low-cost Ti–Al–V–Fe alloy via electron beam cold hearth melting

Abstract

To explore the optimal thermomechanical processing parameters (TMP) of Ti–Al–V–Fe alloys with direct rolling potential after electron beam cold hearth melting (EBCHM) and the grain refinement mechanism during thermal deformation, the multi-pass hot deformation and dynamic recrystallization (DRX) behavior of Ti–4Al–2.5V–1.5Fe alloy ingot produced via EBCHM were investigated in this paper. The multi-pass compression tests were conducted on a Gleeble-3500 thermal simulation experimental machine with deformation temperatures of 850–1000 °C and strain rates of 0.01–1 s−1. The results showed that the flow stress and the microstructure of the alloy were both sensitive to the deformation temperature and strain rate. The as-cast Ti–4Al–2.5V–1.5Fe alloy had the highest fraction of DRX and the smallest average grain size at the deformation temperature of 950 °C and the strain rate of 0.01 s−1 suggest that the DRX mechanism had a significant grain refinement effect. The softening mechanism at higher deformation temperature or lower strain rate was dominated by dynamic recrystallization (DRX). In the continuous dynamic recrystallization (CDRX) mechanism, sub-grain boundaries transformed LAGBs into HAGBs by continuously absorbing dislocations, which was more evident at low deformation temperatures compared to discontinuous dynamic recrystallization (DDRX). In this paper, the original coarse cast titanium alloy grains were refined to smaller sizes through multi-pass thermal deformation, the synergistic regulation laws of thermal deformation behavior and microstructure evolution under different deformation conditions, and the corresponding DRX behavior were elucidated, providing scientific guidance for the direct rolling of cast titanium alloys.