A Study of Solute Trapping During Rapid Solidification of Binary Alloys

Abstract

BACKGROUNDThe very high crystal growth rates which can be produced during pulsed-laser melting provide the opportunity to study non-equilibrium solidification effects under well-defined experimental conditions. In particular, incorporation of solute into the growing crystal in excess of equilibrium solubilities may be achieved. This solute trapping may be pronounced at the highest crystal growth rates and may lead to the absence of microsegregation in non-planar solidification fronts.Crystal/liquid interface kinetics have been treated by considering the diffusive motion of atoms in the liquid. In this treatment, the crystal growth speed can never exceed the maximum diffusive speed of solute in the liquid, hence solute trapping is not possible. More recently, the collision-limited growth model indicates that for metallic and other simple molecular systems, the speed of sound in the liquid should be the upper limit to crystal growth rates. Consequently, in this latter model of solidification, the crystal growth rate can greatly exceed the maximum solute diffusive speed and solute trapping is possible.