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 (αp) and lamellar α (αL) in β phase transformation microstructure (βt) were analysed separately, and the orientation relationship among αp, αL 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 αL variants with the same texture components and interweave to form a basketweave βt structure under the air-cooling condition. The αp without Burgers orientation relationship (BOR) with β phase exhibited obviously texture component without overlapping the αL texture component. The volume fraction of αp 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 αL in the same orientation formed an α colony. A typical 3 variant colonies which were related to each other were observed. Consequently, the αL spatial orientation distribution showed more heterogeneity. Moreover, the BOR between αp and β and the same orientation of some αL and the surrounding αp grains resulting in the overlapping of αp texture component and αL texture component. At last, the relationship between microstructure and tensile properties was analysed.