Microstructure Evolution during High-Temperature Deformation of Ti-5Al-5V-2Mo-1Cr-1Fe Alloy under Compression

Hot isothermal compression testing of Ti-5Al-5V-2Mo-1Cr-1Fe alloy exhibiting lamellar (alpha/beta) microstructure was performed using a deformation simulator. The flow curves of the alloy were obtained as a function of temperature around its beta transus ('T-beta', the allotropic transformation temperature from HCP to BCC phase) at different strain rates in the range of 10(-2)-10 s(-1). The apparent activation energy 'Q' for the alloy under these hot working conditions was found to be similar to 644 and similar to 317 kJ mol(-1) in two-phase (alpha + beta) and single-phase beta regimes, respectively. Distinct constitutive relationships for the alloy have been established at various temperature regimes. Dynamic material model was employed to generate the processing maps and thereby evaluate the stable domains for hot working of this alloy. Deformation below the 'T-beta' led to alpha lamellae kinking followed by fragmentation and dynamic recrystallization of alpha phase. While deformation above 'T-beta' resulted in serrated beta boundary, an indicative of dynamic recovery (DRV) of beta phase. The processing maps along with the detailed post-deformed microstructural examination showed that the optimum/safe working domains for processing of the alloy are 'T' = 1123-1163 K and 'epsilon' = 10(-2)-10 s(-1).