Investigation into microsegregation during solidification of a binary alloy by phase-field simulations

Microsegregation within the columnar dendritic array is analyzed by performing a two-dimensional phase-field simulation. The influence of microstructure morphology on microsegregation is studied for various back diffusion conditions. Under the condition of no back diffusion, it is found that for the region without second dendrite arms the simulation result agrees well with the Scheil equation, but for the region with well developed second dendrite arms there is a severe deviation. This deviation is attributed to the dendrtic coarsening and the inhomogeneity of interdendritic liquid concentration caused by various interface curvatures. Under the condition of moderate back diffusion, it is found that the effect of dendritic morphology on microsegregation can be accounted by enhancing the Fourier number which characterizes the solid-state diffusion. However, this effect decreases with enhancing the back diffusion of the system.