Simulation of solidification structures of binary alloys

A discussion of the multiparticle diffusion-limited aggregation model for the simulation of solidification structures from a binary alloy melt under isothermal conditions is presented. The model incorporates simultaneous diffusion of all atoms in the liquid, atom attachment kinetics at the solid/liquid interface, depending on the local number and nature of bonds formed with the solid, and a surface rearrangement process that mimics the capillary (Gibbs-Thomson) effect. The influence of the local surface energy minimisation on the evolution of dendritic and regular lamellar eutectic structures and on the growth rate of a solidified layer is discussed. The role of the next-nearest neighbour interaction on the energy anisotropy of the internal (solid/solid) and external (solid/liquid) interfaces is identified with respect to the development of dendritic, seaweed and regular lamellar eutectic structures. In the case that no chemical driving force exists for the incorporation of solute (impurity) atoms in the solid, a thermodynamic condition is formulated according to which solidification of such solute atoms can yet occur.