AES studies of the oxides formed on iron-chromium alloys at 400°C

Auger Electron Spectroscopy (AES) has been used to study the compositions and properties of the oxides formed at 400°C on Fe-Cr alloys. The alloys investigated consisted of Cr additions of 3%, 9%, 12% and 18%. It is found that for the Cr additions (Cr = 3%), the oxide consists mainly of iron. However, the addition of Cr from 9% up to 18% results in the formation of layered oxides, i.e., Fe₂O₃ exists in the outer oxide/gas interface and Fe_3-xCr_xO₄ in the inner region with the predominant chromium oxide next to the substrate. The additions of Cr ≥ 9% to the alloys retard the oxide growth significantly.