Cathodoluminescence analysis for rapid identification of alumina and MgAl2O4 spinel inclusions in steels

This paper qualitatively explains the differences in the cathodoluminescence (CL) colors of alumina (Al2O3) inclusions in steels and presents a method of distinguishing MgAl2O4 spinel inclusions from other inclusions using CL imaging. It was found that the presence of chromium (Cr) and titanium (Ti) in Al2O3 inclusions increases CL intensity in the red region, while elements that increase oxygen vacancies such as magnesium relatively increase CL intensity in the blue region. We could distinguish MgAl2O4 spinel inclusions, which produce green luminescence, from Al2O3 inclusions by capturing CL images. We were also able to identify MgAl2O4 spinel in an agglomerated inclusion consisting of MgAl2O4 spinal, Al2O3, and MgO from its CL image. Capturing CL images whose wavelength is less than 600 nm simplifies the identification of Al2O3 and MgAl2O4 spinel inclusions because all the Al2O3 and MgAl2O4 spinel inclusions produced blue and green luminescence, respectively. The present study suggests that CL image capture is a rapid identification method for inclusions in steels, especially MgAl2O4 spinel and Al2O3 inclusions, because it takes less than 30 s to obtain CL images.