Abstract
A quantitative theory of the phase boundaries in alloys between the face-centred and the body-centred cubic structures is given. The theory is applied in detail to alloys in which copper is the major constituent. The width of the (α+β) mixed-crystal region is obtained with fair approximation; it is found that the width of this region decreases with increasing valency of the solute element, a result which is in accordance with experiment. The variation with temperature of the limits of the α and β regions is obtained also, and again agreement with observations is fairly satisfactory.