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

Among oxide scales, alpha-alumina (alpha-Al2O3) is the most stable and protective oxide against high-temperature oxidation and corrosion. alpha-Al2O3 forms on heat-resistant alloys by replacing a metastable theta-Al2O3, which provides poor oxidation resistance. Thus, determining the concentration of theta-Al2O3 is critical for evaluating the performance of heat-resistant alloys. Herein, the author developed a method to determine the concentrations of theta-Al2O3 and alpha-Al2O3 in oxide scales on the surface of heat-resistant alloys from the emission intensities of the peaks of alpha-Al2O3 (694.2 nm) and theta-Al2O3 (683.4 nm) observed in cathodoluminescence (CL) spectra. The concentrations of theta-Al2O3 and alpha-Al2O3 on beta-NiAl heated at 1000 degrees C agreed with those estimated from the peak intensities of alpha-Al2O3 and theta-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 (< 10 s), enabling the rapid determination of the durability and performance of heat-resistant alloys.