The formation and evolution of macrozone in Ti-6242S alloy during thermo-mechanical processing

Abstract

In this study, the formation and evolution of macrozone (sharp textured region) in Ti-6242S alloy during thermo-mechanical processing were investigated. In the meantime, the macrozones relating to the evolution behavior of primary α (αp) and β grains were found in obtained bimodal microstructures. As αp grains dissolving in β matrix, the texture intensity of α phase gradually increased, and the macrozones always formed. There existed an abnormal trend between the texture intensity of α phase and the content of αp grains. Because the reason should be notified that, with the heat treatment temperature increasing, the αp grains with small φ tend to be retained. Herein, the parameter φ describes the deviation degree from exact Burgers orientation relationships (BOR, β∆JβBOR) between αp and β grains. Moreover, as the content of αp decreasing, the inhibition effect of αp on the growth of secondary α (αs) colonies weakened, and then increased the area of αs colonies. Under large pre-deformation and heat treatment, the BORs between many αp and their neighboring β grains were destroyed due to the rotation of αp grains. And it was worth noting that β phase was mainly composed of recrystallized grains with high-angle boundaries. These led to a significant decrease in the degree of variant selection (DVS) of αs colonies during β → αs transformation, thus reducing the development of α texture.