The influence of composition on the macrostructures of small ingots has been studied in the systems Al–Sn,Cd–Zn, Bi–Cd, Bi–Sn, and Pb–Sn. In each of these systems an anomaly was observed, within the eutectic horizontal on one side of the eutectic composition, associated with a sudden decrease in equiaxed zone size as the composition changes towards the eutectic. This has been interpreted in terms of the change in type of grain dominating the macrostructural appearance and the poor ability of the primary phase to nucleate the eutectic. The observations give support to the ‘one-way’ nucleation theory.
MST/247
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