Effects of Variations in Operating Conditions on the Precision and Accuracy of Standardless Elemental Analysis of Stainless Steel by SEM-EDS

It is a customary practice to carry out standardless elemental microanalysis by energy dispersive spectroscopy (EDS) under the very same operational conditions as those used for scanning electron microscope (SEM) imaging. In this article, EDS experiments were carried out with stainless steel (SS), varying the EDS testing operating conditions. The results showed that, if X-ray spectra are acquired under operating conditions that are very dissimilar to those optimized for microanalysis, both the detectability limit of minor species (Si, Mo, and Mn) and the uncertainty in the concentration of major alloying elements (Cr and Ni) are noticeably impaired. It was observed that, by improving the signal-to-noise (S-to-N) ratio (i.e., by increasing the accelerating voltage, beam intensity, and total acquisition time, or when the working distance is optimized), the precision of the elemental concentration increases, but the accuracy is only marginally affected. For the major alloying elements, 25% of the measurements showed a percent discrepancy higher than three times the standard deviation, which is inconsistent with a normal statistical distribution.