Automated Mapping of High-Temperature Corrosion Products on Iron Chromium Alloy Using Raman Microscopy

Abstract

An automated Raman microscope mapping system is described which uses single point analysis combined with a stepper-motor-driven microscope stage. Methods for one-dimensional full spectra line-scans and repetitive frequency selective line-scans providing a two-dimensional species map are reported. The technique is applied to a surface feature appearing on a sample of Fe-Cr steel oxidized at 800°C for 143 h. The results suggest that Fe3O4, FeCr2O4 and Cr2O3 develop fairly uniformly across much of the surface and that the formation of raised areas of more extensive corrosion is due to the absence of Cr2O3 in these regions. In addition, a sample oxidized at 675°C for two hours was ball-cratered to provide a Raman depth profile. The corrosion scale was complex—the outermost layer comprising Fe2O3 and some Fe3O4, while the inner layer consisted mainly of FeCr2O4, with some evidence of Cr2O3.