Effect of predeformation on globularization of Ti-5Al-2Sn-2Zr-4Mo-4Cr during annealing

The microstructure evolution during annealing of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was investigated. The results show that for the alloy compressed at 810 degrees C and 1.0 s(-1), deformation amount (height reduction) 20% and 50% and annealed at 810 degrees C, thermal grooving by penetration of beta phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 degrees C, 0.01 s(-1), and then annealed at 810 degrees C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries (HABs) remain With long time annealing, the chain-like a grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti-5Al-2Sn-2Zr-4Mo-4Cr.