Microstructure and texture evolution during the fabricating and hot gas free bulging process of a laser-welded Ti-22Al-25Nb alloy tube

Abstract

To develop a Ti-22Al-25Nb alloy tubular components processing method, UO forming, laser beam welding and hot gas free bulging processes were carried out. Microstructure and texture evolution of β/B2, α2 and O phases were investigated. As for β/B2 phase, new textures (111)01-1 and (111)12-1 emerged during the UO forming process at 800°С. The laser beam welding process was used to build a tube, where the original β/B2-phase rolling texture (001)11-0 were dramatically broke up. Additionally, strong {001}〈100〉 textures appeared, which was associated with columnar grains forming during the laser beam welding process. With the bulging temperature rising from 950°С to 980°С, dynamic recovery played a predominant role in softening mechanism and a rolling texture (111)11-0 emerged. As for α2 and O phases, lath and lenticular α2 phase as well as mixture of α2 and O phases in a lenticular shape were observed in the undeformed joint at 950°C. Precipitated phases along β/B2-phase grain boundaries decreased, with temperature rising from 950°C to 980°C. As the temperature rose, α2 phase underwent more apparent spheroidization and grain size decreased dramatically, which restricted the deformation of α2 phase and β/B2-phase matrix.