Phase diagrams of atomic ordering in alloys with the superstructures L12 and L1o

Abstract

For different values of the atomic interaction in the first and second coordination spheres, phase diagrams of atomic ordering in alloys with an fcc lattice are calculated by the Kikuchi method in the tetrahedron + triangle approximation. In addition to order-disorder transitions, the equilibrium of two ordered phases with the superstructures L12 and L1o and the form of the diagram close to three-phase equilibrium are considered. The calculated diagrams and order-disorder transition temperatures are compared with the analogous results obtained in the tetrahedron approximation. In view of the lack of considerable discrepancy in the results, it may be concluded that the approximation of the entropy of the alloy model in the two approaches is sufficiently good. Hence, the significant difference between the phase diagrams calculated in the present work and the phase diagrams of real alloys is mainly due to the different types of atomic interaction in these alloys.