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, αLand 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 αLvariants with the same texture components and interweave to form a basketweave βtstructure under the air-cooling condition. The αpwithout Burgers orientation relationship(BOR) with β phase exhibited obviously texture component without overlapping the αLtexture component. The volume fraction of αpin 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 αLin the same orientation formed an α colony. A typical 3 variant colonies which were related to each other were observed. Consequently, the αLspatial orientation distribution showed more heterogeneity. Moreover, the BOR between αpand β and the same orientation of some αLand the surrounding αpgrains resulting in the overlapping of αptexture component and αLtexture component. At last, the relationship between microstructure and tensile properties was analysed.