Defects and diffusion in prototypes of shape memory alloys; Part II β₂' Au-Zn alloys

Abstract

We have briefly reviewed self diffusion studies in the β2 Au-Zn alloys conducted in the past as function of temperature, composition, pressure and the isotope effect using radioactive tracers of both the constituent species. We have also compared the densities computed from the x-ray lattice parameters with those actually measured in a large number of single crystals having nominal compositions of Au - 49, 50 and 51 at. % Zn. The various data are compiled and critically discussed. Much has been learnt from the self diffusion studies and the density differences about the nature of the atomic defects present in this alloy system. A definite presence of the antisite atoms and vacancy complexes has been inferred. Self diffusion in the stoichiometric alloy occurs by six correlated atom-vacancy interchanges between the atoms residing on the two sublattices. In the off-stoichiometric alloys, diffusion by the anti-site bridge mechanism, involving antisite atom-vacancy complexes, is an additional process in both the Au and Zn rich alloys. We hope that the information provided in this article will be of general use for studies of other properties in this alloy system such as the martensitic transformation.