Untersuchung von Oxidationsprozessen an Oberflächen von FeCr-Legierungen und Austenitstahl mittels Röntgenabsorptionsspektroskopie unter streifendem Einfall

Abstract

The surface oxidation of stainless steel and FeCr alloys with 18, 28, and 43 mass-% Cr was investigated in situ using grazing incidence X-ray absorption spectroscopy (GIXAS) at chromium and iron K-edges.<br /> In the temperature range from 290 K to 680 K, the oxidation in air was monitored in situ for all samples. Additionally, the stainless steel samples were oxidized ex situ at temperatures up to 1173 K. The influence of sample preparation, i.e. mechanical and electrolytical polishing, on surface structure and GIXAS measurements was investigated.<br /> The standard GIXAS data analysis was extended to the treatment of a single layer model in order to estimate the oxide layer thickness as well as the chromium concentrations in the oxide layer and in the near-interface substrate.<br /> XANES analysis shows transitions from b.c.c. Fe to corundum type Fe2O3 and from b.c.c. Cr to corundum type Cr2O3 in all cases. On the FeCr alloys the initial oxide layers at room temperature are 1.1-1.4 nm thick and contain 60-90 mass-% chromium, while the near-interface substrate is depleted in Cr.<br /> During heating, Fe oxide growth dominates up to 560-600 K. Then the chromium oxide layer loses its passivation effect and Cr oxidation sets in. FeCr alloys were shown to be suitable model systems for the oxidation of stainless steels.