MEASUREMENT OF INTERDIFFUSIVITY BY QUANTITATIVE X-RAY-MICROANALYSIS USING ANALYTICAL ELECTRON-MICROSCOPE IN NI-AL SYSTEM

The energy dispersive X-ray microanalysis in an analytical electron microscope (AEM-EDS) which provides a high spatial resolution was used to measure interdiffusion coefficients in the Ni-Al binary system. Electron transparent thin specimens were prepared from a Ni/Ni-8 mol%Al diffusion couples. A modified technique was introduced to avoid breaking at the couple interface during preparation of thin specimens. The absorption correction required for the AlK(alpha) line was achieved by the differential X-ray absorption (DXA) method. A comparison showed that the agreement was fairly good between the results of the AEM-EDS and the electron probe microanalysis (EPMA). Thus, it was suggested that AEM-EDS can be used for the measurement of interdiffusivities as an alternative to EPMA, particularly at lower temperatures where a high spatial resolution is required. The interdiffusivities measured in this study are compared with other reported values. The interdiffusivities of this study are consistent with the impurity diffusivities of Al in Ni reported in other studies, but higher by an almost order of magnitude than the reported self-diffusivities of Ni in Ni. The diffusion periods and temperatures necessary for AEM-EDS were discussed in comparison with those for EPMA.