FORMATION OF NICK INSTABILITIES DUE TO PARTICLE CLUSTERING ALONG CRYSTAL INTERFACES

The kinetic growth of crystal grains is simulated on a square lattice in the presence of mobile particles. The model is based on the Eden an d the dynamic epidemic models. Trapping of the particles by the advanc ing front and a short-range repulsion of the particles by the front ar e both allowed. The grain boundary morphology is studied through the k ink density concept and the spatial distribution of particles is discu ssed. Indeed, the clustering of particles along the crystal edges is f ound to induce the formation of so-called nick instabilities at the li quid-solid interface. The particles, when trapped near such instabilit ies, occur as oblique filamentary structures in the crystal matrix, ju st like river networks. These findings agree with recent experimental observations. The numerical laws are also explained by theoretical arg uments based on different characteristic lengths.