Strain-induced variant selection in heterogeneous nucleation of alpha-Ti at screw dislocations in beta-Ti
M Poschmann and J Lin and H Geerlings and IS Winter and DC Chrzan, PHYSICAL REVIEW MATERIALS, 2, 083606 (2018).
Heterogeneous nucleation of the alpha to beta phase transition at < 1 1 1 >(beta)-type screw dislocations in pure titanium is examined through a combination of elasticity theory and molecular dynamics simulations using a modified embedded atom method potential. These screw dislocations act as heterogeneous nucleation sites and increase the alpha phase growth rate but also restrict the orientation of the alpha nuclei to certain directions, along which the strain field of the dislocation aligns with the strain required to complete the Burgers transformation path. Simulations and elasticity theory predict the same three alpha phase variants along the same preferential directions for alpha nucleus growth in the early stages of transformation. Previous elasticity theory calculations indicate that this growth does not result in the elastically preferred habit plane for the alpha nucleus. Molecular dynamics simulations on many-layer supercells presented here show that large alpha plates will change their growth direction toward the predicted habit plane, but this rotation is resisted by the line tension of the dislocation until the alpha precipitate detaches from the dislocation.
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