Morphology transformation of primary strip α phase in hot working of two-phase titanium alloy

Microstructural development in hot working of TA15 titanium alloy with primary strip α structure was investigated with the aim to globularize α strips. Results show that the mechanisms of morphology transformation are the same to the spheroidization mechanisms of lamellar structure. Boundary splitting and termination migration are more important than coarsening due to the large size of strip α. The α strips are stable in annealing due to the unfavorable geometrical orientation of intra-α boundaries, the large thickness of strip and the geometrical stability of α particles. Predeformation and low speed deformation accelerate globularization of α strips in the following ways: direct changing of particle shape, promotion of boundary splitting and termination migration by increasing high angle grain boundaries and interfacial area, promotion of coarsening by forming dislocation structures. Large predeformation combined with high temperature annealing is a feasible way to globularize strip α.