Primary dendrite spacing of lead dendrites in Pb-Sn and Pb-Au Alloys

Abstract

Directional solidification experiments have been carried out on dendritic alloys of Pb-Sn and Pb-Au as a function of temperature gradient,G, solidification rate,R, and composition. Variation of temperature gradient was carried out at a moderate growth rate, 20 µm/s, and variation of growth rate was carried out at high gradients, around 350 °C/cm. Based on these experiments the primary dendrite spacings, λ, are found to follow the correlation λ =kG −a R -b only at rates above 45 µm/s in Pb-Sn alloys and above 10µm/s in Pb-Au alloys. Below these rates λ becomes essentially constant with rate. Possible causes of this break in the rate data are discussed. The values of the exponentsa andb at the higher rates are found to be significantly different from the values predicted by the recent theoretical model of Hunt.