Nondestructive Identification of Internal α-alumina Scales on Heat-resistant Ni–Al Alloys Based on Cathodoluminescence Spectra

Identifying internal α-alumina (α-Al2O3) scales is critical for evaluating the performance of heat-resistant Ni–Al alloys. This study investigated the possibility of using cathodoluminescence (CL) spectra of the alloy surface for nondestructive identification of internal α-Al2O3 scales underneath multiple other scales. The presence of internal α-Al2O3 scales on a heat-treated Ni-14Al alloy was confirmed by the detection of a CL peak at 695 nm. The scales of this alloy comprised NiO on top followed by NiAl2O4 underneath and α-Al2O3 at the bottom with thicknesses of 1.1, 0.8, and 0.5 µm, respectively. The intensity of the CL peak at 695 nm was close to the minimum detectable analyte signal intensity. These results demonstrate that surface CL spectra can be used for the nondestructive identification of internal α-Al2O3 scales on Ni–Al alloys that are underneath multiple other scales.