Deformation behaviour and microstructural evolution during the hot compression of Ti-5Al4Zr8Mo7V alloy

Abstract

The hot deformation behaviour and microstructural evolution of a metastable β titanium alloy Ti-5Al4Zr8Mo7V at deformation temperatures of 775, 795, 815 and 835 ℃ with true strains of 0.25, 0.50 and 1.00 over a strain rate range of 0.001-1 s−1 were investigated to optimize the hot working process window. An Arrhenius type constitutive equation is obtained to describe the hot deformation characteristics. The flow stress behaviour and the deformation thermal activation energy of 187 kJ/mol indicate dynamic recovery of the alloy. Based on the hot compression data, the processing maps at strains of 0.25, 0.50 and 1.00 are constructed to characterize the hot workability. Microstructural investigation confirms the occurrence of flow localization at the predicted unstable region. Whereas, globularization of α phase, dynamic recovery and dynamic recrystallization of β phase are the main dynamic softening mechanisms. The results show that the hot workability of Ti-5Al4Zr8Mo7V alloy is better at higher deformation temperature, higher strain, and lower strain rate, in which case the original microstructure is replaced by the equiaxed α phase and recrystallized β phase.