Variant selection by dislocations during α precipitation in α/β 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 α precipitation in α/β titanium alloys. It is found that, for the dislocation configurations considered in the current study, the elastic interaction between α precipitates and dislocations dominates variant selection during the nucleation stage, whereas the habit plane orientations of α 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 α 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 α variant. Two types of frequently observed clusters of α variants are found to share either a common <1 1 1>β axis or a common {1 1 0}β plane. The primary tent structure is able to induce the nucleation of secondary α 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 α precipitation and the elastic interaction between dislocation and precipitate.