Elemental distributions around the oxide scales/alloy interfaces by SIMS and GDOES analyses

The oxide scales formed on Fe-Cr alloys in CH₄-H₂O gas mixtures (at 1073 K for 3-1050 h) were precisely analysed by SIMS and GDOES. Depth profiles were compared between SIMS and GDOES. They were almost consistent with each other with some differences in minor elements. In depth profiles, the following three zones were identified from surface to internal oxides: Mn and Fe rich layer, Cr-rich layer, and Si-rich layer. The elemental distributions at different depths were investigated by the SIMS imaging technique. Concentration differences of some elements at grain and grain boundaries were imaged at the resolution of urns. The grain boundary diffusion of cations in the alloys was clearly visualized, and the grain boundary diffusion plays an important role in the formation of oxide scales.