Cross-Sectional Investigations of Oxide Scale Nanocrystalline FeCr Alloys after High-Temperature Oxidation Test at 900°C

Abstract

The cross-sectional examinations of oxide films formed by oxidation on the surface of FeCr alloys with various crystallite sizes were observed and investigated. X-ray diffraction (XRD) analysis was used to characterize the oxide scale morphology and to identify the phases and oxidation products. Furthermore, Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) have been used to study the cross-sectional oxides produced by specimens after oxidation process. The cross-sectional investigation shows that the oxide scale formed on the surface of FeCr alloys consisted roughly of Cr2O3 with a small amount of FeO mixture. The outward diffusivity of Chromium to form Cr2O3 protective layers vary significantly occurrences on the surface of FeCr alloy with smallest crystallite size (38.51 nm), the scale had an enriched Cr content which improves the adherence of the oxide scale to the substrate, in another word, it increases the oxidation resistance. While the oxide scale formed on the surface of FeCr alloy with largest crystallite sizes (76.60 nm) had an enriched Fe content which reduces the resistance to oxidation, and adherence to the substrate. The thickness of oxide scale formed on nanocrystalline FeCr alloy with smallest crystallite sizes was found around 8 μm thick, which three-time thinner than FeCr alloy with largest crystallite sizes.