GRAIN refinement is a very common treatment in casting plants to produces fine equiaxed grain structures and enhance chemical homogeneity. Although both subjects have been deeply studied over the past decades, there are few reports dealing with the link between grain refinement and microsegregation. The physical basis of microsegregation also needs more elucidation. PhasePot was used to systematically investigate the effect of grain refinement on microstructure and microsegregation in a eutectic binary alloy.

Simulations were performed on a two-dimensional domain of 325x250 grid size, with grid spacing of 1500 nm and a time increment of 200 ns. Symmetric boundary conditions were applied on all sides of simulation domain for calculation of phase, temperature, and concentration fields. Cooling rate of 104 K/s was applied in all simulations. The simulation domains initially consist of the liquid phase with homogeneous concentration field and different numbers of randomly distributed initial solid seeds. Systems with low initial seeds were considered as poor inoculation conditions, whereas systems with high initial seeds were considered as medium to strongly inoculated.

The simulations show how increasing the number density of inoculant particles results in the reduction of the average grain size and in a change of morphology from dendritic to globular. The combination of these two effects results in a complex trend, manifested by a non-monotonic correlation between the level of microsegregation and the number density of the inoculants. This means that, in contrast to the predictions of the commonly used Scheil model, there can be a specific number density of seeds for which microsegregation is at the highest level.