An X-ray diffraction study was made of fault formation in these alloys. Approximate analyses were performed in order to distinguish between the effects of dispersion and micro-deformation. The data revealed that the introduction of Zn into the face-centered cubic Ni lattice led to a decrease in the effective crystallite size, but led to an increase in micro-strain and in the probability of stacking fault formation. This was consistent with the suggestion that the introduction of foreign atoms into the matrix increased the tendency to stacking-fault formation. It was recalled that the geometry of a stacking fault in a face-centered cubic lattice was analogous to an array of atomic layers which were ordered as in an hexagonal close-packed structure. It was therefore assumed that the stacking fault formation probability depended upon the difference between the stabilities of face-centered cubic and hexagonal close-packed structures under given experimental conditions. Thus, the migration of Zn atoms into the face-centered cubic Ni lattice caused the formation of the hexagonal close-packed arrays of atomic layers which made up the stacking fault. Therefore, upon increasing the Zn content from 0 to 39at%Zn, the formation probability of hexagonal close-packed ordered arrays of atoms was expected to increase if the difference between the thermodynamic stabilities of the 2 lattices became smaller.

E.D.Vladkova, G.P.Vassilev: Crystal Research and Technology, 1994, 29[3], 369-72