Influence of Interphase Anisotropy on Lamellar Eutectic Growth Patterns

It is well documented in many experiments that crystallographic effects play an important role in the generation of two-phase patterns during the solidification of eutectic alloys. In particular, in lamellar composites, large patches of perfectly aligned lamellae are frequently observed. Moreover, the growth direction of the lamellae often markedly differs from the direction of the temperature gradient (the lamellae are tilted with respect to the main growth direction). Both of these effects cannot be explained either by the standard theory or the available numerical models of eutectic growth, which all assume the interfaces to be isotropic. We have developed a phase-field model in which the anisotropy of each interface (solid-liquid and solid-solid) can be separately controlled, and we have investigated the effect of interface anisotropy on the growth dynamics. We have found that anisotropy of the solid-solid interphase boundary free energy dramatically alters the growth dynamics. Tilted lamellae resulting from the modified equilibrium condition at the triple lines, is in good agreement with a theoretical conjecture proposed recently. In three dimensions, the interphase boundaries tend to align with directions of minimal energy. We have also performed simulations in which two grains with different anisotropies are in competition. In all cases, the grain containing the boundaries with the lowest energies was selected after a transient. These results shed new light on the selection of growth patterns in eutectic solidification.