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