Characterization of α-Al₂O₃ in Structural Isomers of Alumina Formed by Oxidation of Fe–Cr–Al Alloys

抄録

To understand the formation of structural isomers of alumina (Al₂O₃) on the surfaces of Fe–Cr–Al alloys, cathodoluminescence (CL), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used. The alloys were annealed under oxygen at a low partial pressure to focus on the initial formation of Al₂O₃. XRD revealed that corundum (α-Al₂O₃) was predominantly formed on the alloy surfaces after annealing at approximately 1100°C, whereas γ-Al₂O₃ and θ-Al₂O₃ were formed at 1000°C. CL peaks around 700 nm, which originated from Cr³⁺ ions in Al₂O₃, was drastically increases by rising the annealing temperatures from 1000 to 1100°C because of the increase of the chromium content in the Al₂O₃ scales that was revealed by XPS. EPMA revealed that the surficial α-Al₂O₃ had striped patterns, which were similar to those observed using CL imaging, indicating that CL can be conveniently used for imaging α-Al₂O₃ and analyzing the inhomogeneous distribution of α-Al₂O₃ on the alloys.