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 spinel, 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.