Phase field simulation of the columnardendritic growth and microsegregation in a binary alloy

This paper applies a phase field model for polycrystallinesolidification in binary alloys to simulate the formation and growthof the columnar dendritic array under the isothermal and constantcooling conditions. The solidification process and microsegregationin the mushy zone are analysed in detail. It is shown that under theisothermal condition solidification will stop after the formation ofthe mushy zone, but dendritic coarsening will progress continuously,which results in the decrease of the total interface area. Under theconstant cooling condition the mushy zone will solidify and coarsensimultaneously. For the constant cooling solidification,microsegregation predicted by a modified Brody-Flemings model iscompared with the simulation results. It is found that the Fouriernumber which characterizes microsegregation is different for regionswith different microstructures. Dendritic coarsening and the largerarea of interface should account for the enhanced Fourier number inthe region with well developed second dendritic arms.