Microsegregation In Cellular Solidification

Microsegregation in a binary alloy solidified in the form of deep cells is predicted using a simplified finite difference model. The model accounts for solid state diffusion and for flow of liquid between cells driven by solidification shrinkage. Cell tip undercooling is predicted using the expression originally derived by Bower et al. Cells are assumed to be cylindrical, and solid state diffusion along the cell axis is ignored, simplifying considerably prediction of solid state diffusion and cell shape behind the tip, which are treated as a one-dimensional moving boundary problem. Experiments were conducted on binary Al-4.5 wt pct Cu, solidified in the cellular growth regime using a Bridgman furnace. Microsegregation in the samples was measured and is compared to predictions; good agreement is found, both for cell heights and microsegregation in the fully solidified material. It is found that intercellular fluid flow exerts a small, but discernable, influence on microsegregation and cell shape.