Osmotic convection-driven instability and cellular eutectic growth in binary systems

Using phase-field theory we demonstrate that osmotic stress may result in intense convection in solidifying eutectic systems. Under isothermal conditions the natural convection is of osmotic origin, and driven by the non-equilibrium composition field. Osmotic forces arise mostly in the interface layer, since large concentration gradients are localized near the triple junctions of the phases. Tuning friction forces at the solid–liquid interface controls the intensity of fluid flow. We have found that convection in the low friction regime significantly affects microstructural pattern formation. Osmotic convection-driven instability of the solid–liquid interface is observed that leads to cellular and dendritic eutectic crystal growth. The mechanism we propose is distinct from diffusive instability that is widely acknowledged as the main cause of cellular and fingerlike patterns.