  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 result from the modified equilibrium condition at the
triple lines, 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.
