An interface-tracking numerical method for rapid planar solidification of binary alloys with application to microsegregation

Many rapid solidification processes, such as splat cooling, melt-spinning, thermal spray deposition and laser surface melting, can result in a planar solid/liquid interface with a large melt undercooling at the interface. On the other hand, when cellular or dendritic solidification takes place, the solute redistribution between cells or dendrite arms can also be assumed in first approximation to be a planar solidification process. Because of the existence of a large melt undercooling, complex non-equilibrium kinetics relationships must be introduced at this interface. These kinetics relationships relate the interface growth velocity to the temperature and solute concentrations at the interface. The accurate calculation of these interface parameters is therefore essential for any numerical model of such rapid solidification processes. In this work, an iteration scheme based on an interface-tracking technique with a linear coordinate transformation is introduced to solve the problem of rapid planar solidification of binary alloys. This numerical technique is very stable and efficient. As an example, the method is applied to analyze the microsegregation of solute during rapid solidification of an Al-4.5wt.% Cu alloy into an undercooled melt. In particular, a solute-rich center region is predicted, in significant contrast to the simpler Scheil model predictions but in good agreement with experimental observations. (C) 1997 Elsevier Science S.A.