Grain-Ripening of the Lead-Rich Phase in Partially Molten Pb-Sb-Sn and Pb-Sb-Sn-As Solders

Abstract

The growth kinetics of lead-rich grains in partially molten Pb-Sb-Sn and Pb-Sb-Sn-As alloys has been studied. In alloys containing one solid phase, the average grain size d is related to the time t by the equation d ³ – d ₁ ³ = K ₁(t – t ₁), as predicted by a model which assumes that liquid diffusion is the ratecontrolling process. The measured activation energies were larger than those usually found for self-diffusion in liquids. The presence of a second solid phase tended to limit the grain growth of the lead-rich phase increasing the time exponent from 3.0. An increased fraction or finer distribution of the second phase restricted the grain sizes to a greater extent. For a constant distribution and quantity of the second phase the kinetics increased and then decreased with increasing fractions of liquid due to an increased percentage of antimony.