Long-period superlattice formation in Cu-rich γ-brasses

The structure of γ-brass has been investigated by electron diffraction and microscopy. The results show that a long-period superlattice forms on Cu-rich γ-brasses containing less than ≈59 at% Zn. The period of the structure varies with composition ranging from 78.7 Å at 56.5 at% Zn to 160.5 Å at 58.6 at% Zn. The superlattice can be closely described as a shear structure with a shear 1/3[001] on (110) planes of the cubic γ-brass structure. However, it is shown that the superlattice cannot be a true shear structure since the observed shear does not of itself accommodate changes in composition.