A quantitative study of solute diffusion field effects on heterogeneous nucleation and the grain size of alloys Original Research Article

The nucleation ability of inoculating particles inside the solute diffusion zone around growing grains during alloy solidification is studied using a spherical, equiaxed dendritic grain model coupled with a new modified free growth model to predict the final grain size of cast aluminium alloys with improved accuracy. We show that the nucleation potency of inoculating particles is reduced by the solute field that develops close to existing, growing equiaxed grains under near isothermal conditions. Solute suppressed nucleation leads to much lower nucleated grain densities, higher nucleation undercoolings and longer times to recalescence when further nucleation events are halted. Under solute suppressed conditions, nucleation events occur in two stages: an initial transient nucleation before significant solute build-up and then continuous nucleation. The significance of the transient nucleation regime depends upon the size of the transient solute diffusion zone, and has been explored using the model. Model predictions suggest that the grain refinement of alloys of high solute content is controlled primarily by solute suppressed nucleation conditions.