Ni-based binary systems with some alloying elements of interest in superalloy design; = − and = (NA1/3 − NB1/3) , where Ni is the element A. We observe that those binary systems in which L12 (AuCu3-type) compounds occur at the composition A3B occur in a particular region (shaded) of the map. The Ni–Co system, being close to the origin, has low energy in the Ni–Co (atom-pair) bonds and there are no ordered compounds in the system. Ni3Fe is an L12 compound close to the origin; it has a lower ordering temperature of 790 K in comparison with the other L12 compounds. The morphology of the AuCu3-type precipitates in the Ni matrix of superalloys is determined by the mismatch in their lattice parameters with respect to the Ni matrix (Jena & Chaturvedi, 1984). The lattice parameters of the L12 compounds can be deduced from Fig. 10.