Abstract
The very early stages of KCl-induced corrosion of a FeCrAl and a FeNiCrAl alloy in an O2/H2O environment were studied using in-situ Environmental Scanning Electron Microscopy (ESEM). The samples were KCl contaminated and then exposed to lab air at a total pressure of 4.8 Torr at 450°C. After exposure, the samples were analyzed using SEM-EDX, FIB and STEM-EDX. For both alloys, fast oxide growth occurred at the KCl particles. Far away from the KCl particles, a thin base oxide formed with potassium chromate nodules on top. The base oxide was layered, consisting of iron-chromium oxide on top and alumina in the bottom part. The FeCrAl alloy suffered internal oxidation while the FeNiCrAl did not. Both alloys formed sub-scale chlorides. A mechanism is proposed for the reaction of KCl on the surface and for the formation of different surface features at the KCl particles.
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