CELL TO DENDRITE TRANSITION IN TIN BASE ALLOYS

Abstract

The transition from cellular growth to dendritic growth was investigated for dilute binary alloys of zone-refined tin with lead, bismuth, and antimony in terms of the rate of growth R, the temperature gradient in the liquid ahead of the solid-liquid interface G, and the solute concentration C₀. It was found that a previous relationship describing the transition for lead base alloys applied, at least to a first approximation, for the low solute concentration tin results. At the high concentrations of solute, however, it was necessary to introduce another variable, namely the cell size at transition d_t. The transition relationships only applied for alloy systems with a distribution coefficient k₀, less than unity. For systems with k₀ > 1 (antimony in tin) a k₀ < 1 was used which was equivalent to the k₀ > 1. A method is described for determining this "equivalent k₀".