LVII. The effect of four transition metals on the α/β brass type of equilibrium

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Abstract
Copper is able to dissolve both zinc and aluminium, and in the binary systems Cu-Zn and Cu-Al there are typical primary (α) face-centred-cubic solid solutions, and body-centred-cubic (β) phases, which are 3/2 electron compounds. In these and other similar alloys of copper, the equilibrium between the α and β phases is determined mainly by the electron concentration, provided that the size-factors are favourable and the electrochemical factors are small. The present paper describes an experimental investigation of the effect of manganese, iron, cobalt and nickel on the α/β equilibrium in Cu-Zn and Cu-Al alloys at 672° C. For this purpose the isothermal sections of the ternary systems in the regions concerned have been determined by the method of annealing and microscopical examination. If it is assumed that the α/α + β and α+β/β solubility curves in the ternary isothermal sections are lines of constant electron concentration, the results show that, when present in small quantities, Ni, Co, Fe and Mn act as though they possessed valencies of about 0·6, 0·8, 1·0 and 1·9 respectively, in the systems Cu-Zn-Ni, Cu-Zn-Co, Cu-Zn-Fe, Cu-Zn-Mn, Cu-Al-Co, Cu-Al-Fe and Cu-Al-Mn. If the simple collective electron theory is assumed, the apparent valencies for nickel, cobalt and iron are approximately equal to the numbers of s-electrons per atom in the crystals of the metallic elements concerned. For manganese the apparent valency agrees with the divalent state previously proposed for this element. The results for the system Cu-Al-Ni are anomalous. The bearing of these results on the theory of the transition metals and their alloys is discussed.

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