Variant selection, coarsening behavior of α phase and associated tensile properties in an α+β titanium alloy

Effect of cooling rates, i.e., air cooling and furnace cooling, after solution in α+β phase-field on variant selection, coarsening behavior of α phase and microstructure evolution were investigated in α+β TC21 alloy. The textures of primary α (α_p) and lamellar α (α_L) in β phase transformation microstructure (β_t) were analysed separately, and the orientation relationship among α_p, α_L and the parent β phase were studied. In addition, the influence of the microstructure characteristics on the tensile properties was investigated. The results showed that all parent β grains, despite their different orientations, produced 12 ideal α_L variants with the same texture components and interweave to form a basketweave β_t structure under the air-cooling condition. The α_p without Burgers orientation relationship (BOR) with β phase exhibited obviously texture component without overlapping the α_L texture component. The volume fraction of α_p in the furnace-cooled sample (about 50%) was higher than that of the air-cooled sample (about 12%), while the size of it slightly increased with decreasing the cooling rate. In each β grain, the thick α_L in the same orientation formed an α colony. A typical 3 variant colonies which were related to each other were observed. Consequently, the α_L spatial orientation distribution showed more heterogeneity. Moreover, the BOR between α_p and β and the same orientation of some α_L and the surrounding α_p grains resulting in the overlapping of α_p texture component and α_L texture component. At last, the relationship between microstructure and tensile properties was analysed.