Electron-probe microanalysis of light elements in multiphase diffusion couples

Wavelength-dispersive electron-probe microanalysis of transition metal carbide and nitride diffusion couples was investigated as a tool to quantitatively determine portions of phase diagrams. In cross-sections, diffusion couples generally show a sequence of several phases composed of crystallites with different orientations and hardness values. Thus, the polishing procedure can adversely affect the accuracy of the analysis due to creation of an uneven surface (relief effect). In addition, as a result of the polishing process the edges of the samples are rounded so that the concentration at the original sample surface is difficult to measure. The most rapid and straightforward procedure to detect influences of the relief effect is a plot of the non-normalized analytical total vs. distance, even where the concentration profile is discontinuous at the interface between phase bands. It is shown that careful experimental preparation, as well as the application of restricted diffusion geometry, has several advantages for establishing phase diagrams.