Dynamic recrystallization mechanism and twinning behavior in hot deformation of Ti-46.5Al-2Nb-2Cr with initial duplex microstructure

The dynamic recrystallization (DRX) mechanism and twinning behavior of Ti-46.5Al-2Nb-2Cr in the alpha + gamma two-phase region were investigated in this work. Isothermal compression of Ti-46.5Al-2Nb-2Cr with initial duplex microstructure was performed at the deformation temperatures of 1180-1260 degrees C, the height reductions of 20-60% and strain rates of 0.001-1.0 s- 1. Quantitative characterization of grain boundary misorientation, local misorientation and geometrically necessary dislocation (GND) density in the gamma phase was made to investigate the DRX behavior. The results showed that DRX occurred in the gamma grains and the gamma lamellae of the alpha 2/gamma lamellar colonies as the height reduction increased, and the interaction between the deformation temperature and the strain rate influenced the volume fraction of the recrystallized gamma phase. Discontinuous DRX (DDRX) via nucle-ation and grain growth dominated the DRX in the gamma phase at a strain rate of 0.001 s- 1, in which the volume fraction of the recrystallized gamma phase increased with the increasing of deformation temperature. Continuous DRX (CDRX) via transition from medium-angle grain boundaries (MABs) to high-angle grain boundaries (HABs) dominated the DRX in the gamma phase at a strain rate of 1 s- 1, in which the volume fraction of the recrystallized gamma phase decreased with the increasing of deformation temperature. gamma/gamma twin boundaries were quantitatively investigated. It was shown that gamma true twin (TT) was the main twin component formed in the recrystallized gamma grains. The fraction of the gamma/gamma twin boundaries increased with the increasing of deformation temperature at a strain rate of 0.001 s- 1 and height reduction of 60%, which decreased with the increasing of strain rate at a deformation temperature of 1260 degrees C and height reduction of 60%. Transmission electron microscopy and high -resolution TEM (HRTEM) characterizations of the dislocations and stacking fault (SSF) in the gamma phase showed that the growth of the DDRX gamma grains promoted the occurrence of gamma twin.

Automated summary

This study investigated the dynamic recrystallization (DRX) mechanism and twinning behavior of Ti-46.5Al-2Nb-2Cr in the alpha + gamma two-phase region. Isothermal compressions were performed at various deformation temperatures, height reductions, and strain rates. The DRX behavior was characterized by grain boundary misorientation, local misorientation, and geometrically necessary dislocation (GND) density in the gamma phase. The results showed that DRX occurred in the gamma grains and the gamma lamellae, and the volume fraction of the recrystallized gamma phase was influenced by the interaction between the deformation temperature and strain rate. The study also investigated the gamma/gamma twin boundaries and found that the occurrence of gamma twin was promoted by the growth of the DRX gamma grains.