Influence of interphase boundary anisotropy on bulk eutectic solidification microstructures

The solidification of eutectic alloys generally produces two-phase microstructures. Their morphology is determined by the dynamics of the solid-liquid interfaces at the crystallization front. At the triple lines, where the liquid and the two solid phases meet, solid-liquid and solid-solid surface free energies are in local equilibrium. We perform three-dimensional phase-field simulations with a multi-phase-field model in which the surface free energies can be independently controlled. We find that an anisotropy of the interphase boundary (solid-solid) energy has a strong effect on the microstructural patterns. The lamellae tend to align with directions of minimal interphase boundary energy. For a two-fold anisotropy, as generally expected for interphase boundaries between two cubic crystals, regular lamellar arrays are formed, in strong contrast to the labyrinth patterns observed in isotropic systems. If two different grains compete, the one with the lowest interphase boundary energy always overgrows the other. These results are consistent with observations in bulk metallic eutectic samples, namely, the frequent occurrence of large regular lamellar arrays and the prevalence of grains with special orientation relationships.

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