Cathodoluminescence Analysis for the Nondestructive Evaluation of Silica Scale on an Iron-Based Alloy

Abstract

Information on the composition, morphology, and thickness of surface oxide scale helps to control the performance of heat-resistant alloys. Currently, there is a lack of adequate analytical methods that allow the rapid and nondestructive evaluation of these properties. In this study, we demonstrate a nondestructive method for identifying silica (SiO2) scale and evaluating its morphology and thickness within 1 min by acquiring the cathodoluminescence (CL) images and spectra of SiO2 scale on an Fe–5%Si alloy heated to 900 °C. SiO2 scale emitted yellow–orange, violet, or red luminescence, whereas the other scale products that form on Fe–Si alloys, such as FeO, Fe3O4, Fe2O3, and Fe2SiO4, did not. Thus, we can identify SiO2 scale and observe its morphology on the basis of luminescent color in the CL image. The thickness of SiO2 scale can be correlated to the intensity of the CL peak at 645 nm. Therefore, the acquisition of CL images and spectra is a novel analytical method, which allows one to control the performance of SiO2-forming Fe–Si alloys.