Growth competition during columnar solidification of seaweed microstructures : Insights from 3-D phase-field simulations.

The mechanisms by which interfacial instabilities instigate the growth of solidification patterns is a topic of longstanding interest. In columnar solidification of metallic melts, where the solid-liquid interfacial energy is anisotropic, evolving dendritic patterns compete depending on their relative misorientation. By contrast, organic "plastic crystals", such as alloys based on succinonitrile, where the anisotropy in their solid-liquid interfacial energy is extremely weak, solidify forming seaweed patterns that typically exhibit little, if any, growth competition. We explore in this study mechanisms by which columnar solidification microstructures of binary alloys with low crystalline anisotropy compete. We adopt toward this end a validated Navier-Stokes multiphase-field approach to characterize the influence of grain misorientation, seed morphology, and melt advection on the growth competition. Simulated seaweed patterns indicate profound influences of all three factors, although characteristic solidification morphologies are observed to evolve depending on the melt flow intensity.