Supercooling, Preferred Orientation, and Inverse Segregation in Lead ‐Antimony Alloys

Abstract

Experiments are described which confirm the previously reported inverse segregation of Sb in the Pb‐Sb alloy castings. Supercooling of Sb at eutectic temperatures and a preferred orientation and growth direction for the Sb crystals are responsible for the excessively large coverage by Sb in the surface of the cast alloy. Interdendritic flow, previously claimed as a principal factor in this inverse segregation, is now found to be unnecessary. Preferred orientation with the [111] direction perpendicular to the surface and preferred directions of growth parallel to the (111) plane are shown to be caused by the strong covalent linkages within the (111) pairs of planes. This, plus a number of factors such as temperature gradient, surface tension, and Sb concentration in the surface film, favors the growth of those nuclei that originate with their (111) planes parallel to the surface. This preferred orientation of Sb can influence the tensile strength and ductility of hypereutectic Pb‐Sb alloys.