XPS and AES studies of the high temperature corrosion mechanism of Fe-30Cr alloy

Fe-30Cr alloy specimens were pre-oxidized at two different oxygen partial pressures (10^?16 and 10^?19 atm) at 900°C and subsequently exposed to environments containing both oxygen and sulfur. The sulfur and oxygen partial pressures were maintained such that Cr₂O₃ was the stable phase. The Cr₂O₃ scales formed during pre-oxidation became rapidly unstable when exposed to an environment whose composition approached the chromium sulfide-chromium oxide phase boundary; but when exposed to a higher oxygen partial pressure with the same sulfur partial pressure, the preformed scales remained intact. For elucidating the sulfidation mechanisms, the reaction products on the surface were analyzed at different stages of sulfidation by X-ray photo-electron spectroscopy and Auger electron spectroscopy. Correlation of the reaction mechanisms with thermodynamic and transport parameters are discussed.