ANALYTICAL ELECTRON-MICROSCOPY OF DIFFUSIONAL INTERFACES IN AN AL-22AT-PERCENT-ZN ALLOY

High spatial resolution X-ray microanalysis of thin foils, in a transm ission electron microscope, was applied to determine solute content pr ofiles existing across the ct lamellae formed by discontinuous precipi tation (DP) in an A1-22 at. % Zn alloy. This technique, combined with the in situ observation of the kinetics of the process, allowed us to treat the DP reaction as a local phenomenon. The calculated diffusivit y at a moving reaction front was found to be in good agreement with th e data on diffusion at a stationary grain boundary and, in this way, t he discrepancies resulting from the consideration of the DP as a globa l reaction were eliminated.