Variant selection by dislocations during alpha precipitation in alpha/beta titanium alloys

Through three-dimensional phase-field simulations, dislocations are found to exert significant influences on variant selection and subsequent development of transformation texture during alpha precipitation in alpha/beta titanium alloys. It is found that, for the dislocation configurations considered in the current study, the elastic interaction between alpha precipitates and dislocations dominates variant selection during the nucleation stage, whereas the habit plane orientations of alpha precipitates relative to the dislocation lines play an important role in variant selection during the growth stage. In general, edge dislocations exhibit a much more prominent effect than screw dislocations. Various morphological patterns of alpha precipitates formed by heterogeneous nucleation around dislocations of different configurations are revealed, including clusters of multiple variants and a special tent structure that appears as a pyramid with each of its faces composed of a particular alpha variant. Two types of frequently observed clusters of alpha variants are found to share either a common < 111 >(beta) axis or a common {110}(beta) plane. The primary tent structure is able to induce the nucleation of secondary alpha through autocatalysis, reducing the degree of variant selection. The effect of undercooling on variant selection is also investigated in the context of competition between the chemical driving force for alpha precipitation and the elastic interaction between dislocation and precipitate. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.