Hot deformation and dynamic recrystallization of a near-beta titanium alloy in the β single phase region

Abstract

A new near-β titanium alloy, Ti-5Al-5Mo-5V-3Cr-1Zr (Ti55531), has been widely used in industry due to its relatively wide processing window, high hardenability and strength. This study investigated the deformation and microstructural evolution of the Ti55531 alloy in the β single phase region. Hot compression tests were carried out at temperatures of 860–900 °C and strain rates of 0.001–10 s−1 on a Gleeble-3800D simulator. The metallographic and electron backscatter diffraction (EBSD) techniques were used to analyze the microstructural evolution. The results demonstrate that the stress curves exhibit discontinuous yield and flow softening phenomena, which are very sensitive to temperature and strain. A processing map was developed for this alloy, which shows that the instability increases with the strain. Dynamic recrystallization (DRX) is a typical characteristic in the beta region, which can take place at high temperatures and low strain rates. Based on this analysis, a physically-based deformation constitutive equation and DRX kinetics, critical condition and grain size models were developed. These models were implemented in a DEFORM subroutine to predict the deformation and microstructural evolution of the Ti55531 workpiece during nonisothermal forging. The comparison between the experimental and predicted results shows good agreement, which indicates that the model is reliable and that the subroutine provides an effective tool to predict the deformation and microstructures for industrial production.