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

Abstract

• Each β grains produced 12 ideal α L variants with basketweave morphology in BM1. • The α p without BOR with β exhibited texture component without overlapping α L texture component in BM1. • A typical 3-variant colony was observed in which variants were related to each other in BM2. • The BOR between α p and β and the same orientation of some α L and surrounding α p resulting in overlapping of α p and α L texture component in BM2. • The cooling rate had a significant effect on tensile properties. 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.