On the composition dependence of undercooling in binary alloy melts

Abstract

The driving free energy for nucleation of a primary solid phase from an undercooled liquid solution is an important parameter in the theory of nucleation. In the present study an expression for the driving free energy has been obtained in a form that can be directly related to slopes of liquidus and solidus lines in a phase diagram. The expression has been used for an examination of the composition dependence of the maximum undercooling in alloy droplets of the eutectic systems silver-copper and lead-tin. It has been demonstrated that undercooling of an alloy melt is terminated by the nucleation of a primary phase when the driving force attains a composition-independent critical value. These critical values have been found to vary from experiment to experiment and possibly depend on the nature of the surface coating in the droplet emulsion samples as demonstrated by the results on the lead-tin alloys.