Rapid Determination of α- and θ-Alumina Concentrations in Heat-Resistant Alloys Using Cathodoluminescence Analysis

Among oxide scales, α-alumina (α-Al2O3) is the most stable and protective oxide against high-temperature oxidation and corrosion. α-Al2O3 forms on heat-resistant alloys by replacing a metastable θ-Al2O3, which provides poor oxidation resistance. Thus, determining the concentration of θ-Al2O3 is critical for evaluating the performance of heat-resistant alloys. Herein, the author developed a method to determine the concentrations of θ-Al2O3 and α-Al2O3 in oxide scales on the surface of heat-resistant alloys from the emission intensities of the peaks of α-Al2O3 (694.2 nm) and θ-Al2O3 (683.4 nm) observed in cathodoluminescence (CL) spectra. The concentrations of θ-Al2O3 and α-Al2O3 on β-NiAl heated at 1000 °C agreed with those estimated from the peak intensities of α-Al2O3 and θ-Al2O3 in the XRD patterns. This method can also be applied to areas ranging from the millimeter to micrometer scale and provide a short acquisition time (