Eutectic compositions and liquid immiscibility in certain binary alloys

An examination is made of the compositions of eutectic points in the metallurgical equilibrium diagrams given in Hansen's text-book on The Constitution of Binary Alloys. A large number of eutectics occur at almost 0% of the solute element. With increasing atomic percentage of solute, the number of eutectics in a given composition range diminishes rapidly, until a recovery sets in at 8–10 atomic % solute. There are very few eutectics in the equiatomic region, and at intermediate compositions the eutectic composition distribution curves show a series of peaks at intervals of 7–8 atomic %. Stockdale's suggestion that eutectic points occur at whole number ratios of the two kinds of atom is not confirmed, but certain regions of composition are favoured, and these include the atomic ratios of approximately 1:6, 1:3, 1: 2 and 2:3. The reason for this is discussed, and free energy curves are described; some of these lead to liquid immiscibility. and examples of this are discussed.