The application of high-resolution SEM and EPMA to the study of coatings and interfaces of materials

Abstract

Microchemical and micro-structural analysis are often required when characterizing coatings and interfaces in materials. For coatings the interface between substrate and coating and between coating and the surface are of particular interest. The scanning electron microscope (SEM) and electron probe microanalyzer (EPMA) are often employed in characterizing interfaces in materials particularly because solid samples can be studied and sample preparation is usually restricted to developing a suitable flat polished surface for analysis. Both these instruments are essentially the same although the EPMA is equipped with wavelength dispersive detectors (WDS) and is dedicated to quantitative microchemical analysis.The spatial resolution for high resolution SEM where microstructural analysis of the surface is desired is now in many ways comparable to the transmission electron microscope (TEM). Magnifications of over 100,000 X are available in SEMs equipped with a field emission gun using the secondary electron mode. Figure 1 shows the interface region of a retained austenite region in the Tazewell iron meteorite shown in both TEM and SEM mode and Figure 2 shows the morphology of crystals, 0.3 μm wide by 1.5 μm long containing ledges 30-50 nm wide in an electrodeposited Zn coating on a steel in both TEM and SEM mode.