Atomistic simulation of the step mobility at the Al–Si(111) crystal–melt interface using molecular dynamics

Molecular dynamics simulations and an angular embedded atom method description of interatomic forces have been utilized to compute the mobility of steps on the facetted (111) crystal–melt interface in the binary alloy Al–Si. Two systems were studied: an Al–90%Si alloy in the temperature range of 1560–1580K and Al–60%Si at T=1190–1220K. It was determined that the higher Si content alloy exhibited attachment controlled growth of steps whereas for the lower temperature, higher Al concentration alloy step growth is characterized by a diffusion controlled or mixed mode mechanism. The step mobility, which is the proportionality constant between the velocity and driving force, was determined for the Al–90%Si alloy as a function of temperature and composition. It was found that mobility decreases fairly rapidly with the addition of Al solute. Also, from the variation with temperature, it appears the mobility is proportional to the interdiffusion coefficient in the liquid.