Diffusion and Correlation Effects in Copper-Zinc Alloys

The self-diffusion coefficients of copper in copper-zinc alloys containing 0-4-at.% zinc have been measured at 894.4 and 946.7°C. These results, together with the correlation factor for the diffusion of zinc in copper as determined from measurements of the isotope effect, are used to obtain the relative jump frequencies of the zinc atoms and the neighboring copper atoms by means of the theory of Howard and Manning. The isotope effect for the diffusion of both copper and zinc has been measured in $\alpha$—Cu-Zn alloys containing 4- and 30-at.% Zn, and in ordered and disordered $\beta$—Cu-Zn. The results support Manning's theory of correlation effects in concentrated alloys for those cases where the theory should be applicable (30-at.% Zn and disordered $\beta$—Cu-Zn). The agreement is poorer for those cases where the theory is less applicable (4-at.% Zn and ordered $\beta$—Cu-Zn). The isotope effect for the diffusion of copper is the same in ordered and in disordered $\beta$—Cu-Zn. This supports our earlier conclusion that the Elcock-McCombie mechanism is not the dominant mechanism in ordered $\beta$—Cu-Zn when the state of the order is described by $S=0.7\mathrm{}$.