Dynamic transformation of a near alpha high-temperature titanium alloy during hot deformation

Abstract

The rapid drop of peak flow stress in the initial stage of hot compression experiment was found to be related to the occurrence of dynamic transformation from alpha phase (hcp) into beta phase (bcc) of a near α high-temperature titanium alloy. In order to predict the flow stress at all strain, the dynamic recovery (DRV) model and the Back-Error Propagation (BP) neural network architecture were established and comprehensively utilized to characterize the flow stress, which exhibited high accuracy in tracking the flow behavior at different deformation parameters. The variation of peak flow stress at initial stage of hot compression indicated that the rapid drop extent of peak value increased with the rise of deformation temperature, the decrease of strain rate and the increase of strain. It was worth noting that the dynamic transformation evolution in the microstructure exhibited the consistent variation of peak flow stress with different deformation parameters. The high-magnification microstructure analysis indicated that the dynamic transformation was accomplished by the immigration of α/β interface and the penetration of beta phase into alpha phase from edge to inside, all of which were related to the dislocation motion. The experimental result proved that the dynamic transformation was the dominant factor resulting in the rapid drop of peak flow stress at the initial stage of hot deformation.