A three-dimensional phase-field model for computer simulation of lamellar structure formation in γTiAl intermetallic alloys

A three dimensional phase-field model of α^′₂→α₂ + γ transformation is developed to simulate the formation of coherent multi-domain lamellar structures in γTiAl intermetallic alloys. The model takes into account the effect of coherency strain associated with the lattice rearrangement accompanying the phase transformation, and the anisotropy in interfacial energy. Simulation studies based on the model successfully predicted the essential features associated with the multi-domain lamellar structures observed experimentally. It is shown that the coherency strain accommodation is the dominating factor responsible for the formation of the lamellar structure. The neighboring lamellae of γ phase are found to have either a twin or a pseudo-twin relationship, with the former being dominant. It is found that strain-induced correlated nucleation plays an important role in the formation of the twined lamellae. The lamellar thickness is determined by the interplay among the elastic strain energy, interfacial energy and bulk chemical free energy. Domains within individual lamellae are isotropic and domain boundaries are smoothly curved. No special self-accommodating morphological patterns are observed on the (0001)_α2 plane, which is very different from the pattern formation predicted for the coherent hexagonal → O-phase transformations.