Diffusion Measurements by Analytical Electron Microscopy

Abstract

ABSTRACTThe analytical electron microscope (AEM) has been used to measure the concentration gradients which form in single and multiphase diffusion couples. The procedures used to collect x-ray microanalytical data and reduce that data to elemental compositions are typical of those used to quantify x-ray data generated in thin films. The primary difficulty in analyzing diffusion couples with the AEM is sample preparation. The principle advantage of the AEM as a tool to measure diffusion induced concentration gradients is its high spatial resolution, approximately 20 to 100 times better than that of the electron microprobe which has been traditionally used to measure these concentration profiles. As a consequence, the AEM data can yield diffusivities as much as 5 orders of magnitude smaller than those obtained from electron microprobe data. This paper will review the fundamental principles of the determination of diffusion coefficients from the concentration gradients measured in single and multiphase diffusion couples and the basic considerations of thin foil x-ray microanalysis. With this understanding of the basic concepts, recent studies of diffusion in Ta-W and U-Nb will be discussed.