Effect of zone-refining on the structure of irregular eutectics

Seven eutectic alloys (Pb-Sb, Bi-Cd, Zn-Zn ₃Sb ₂, Bi-BiPb ₂, Bi-Sn, Bi-Zn, and Sn-Zn) made from 99.99% purity components were zone-refined in argon atmosphere to reduce further their impurity content. The zone-refined alloys were zone-levelled and directionally solidified. Several basic morphological changes were observed: coarsening (Pb-Sb), orientation of the minor phase along growth direction, some breakdown of regularity in the complex regular structure (Bi-BiPb ₂, Bi-Sn), and horizontal alignment of the minor phase by rotation about the growth axis (Bi-Cd, Bi-Zn, Sn-Zn). Three classes of refined structures were obtained: irregular (Pb-Sb, Bi-BiPb ₂, Bi-Sn), broken-lamellar (Bi-Cd, Bi-Zn) and broken-rod (Zn-Zn ₃Sb ₂, Sn-Zn).