Static globularization and grain morphology evolution of alpha and beta phases during annealing of hot-rolled TC21 titanium alloy

A lamellar-structure TC21 titanium alloy was hot-rolled and subsequently annealed at 820, 880 and 940 degrees C for 1 and 6 h, and the effects of annealing parameters on static globularization and morphology evolution of both alpha and beta phases were studied. The results show that alpha globularization process is sluggish due to the limited boundary splitting at 820 degrees C. With increasing temperature to 880 degrees C, the accelerated boundary splitting and termination migration promote the alpha globularization. At 820 and 880 degrees C, the static recovery (SRV) and recrystallization (SRX) induce the grain refinement of interlamellar beta phase. However, the excessively high temperature of 940 degrees C results in the coarsening of alpha grains due to the assistance of Ostwald ripening, and produces coarse beta grains mainly due to the absence of SRX in interlamellar beta phases. Conclusively, 880 degrees C is an appropriate annealing temperature to produce a homogeneous microstructure in which globularized alpha and refined beta grains distribute homogeneously.