XPS AND AES ANALYSIS OF PASSIVE FILMS ON FE-25CR-X (X=MO, V, SI AND NB) MODEL ALLOYS

Corrosion resistance of stainless steel is due to the presence of a th in passive film of typically 1-2 nm thickness. The influence of ternar y alloying elements on the composition of passive films on Fe-Cr alloy s and their pitting corrosion resistance has been investigated. Iron-c hromium alloys were analyzed by XPS and AES with model alloys (Fe-25Cr -X with X = at % Mo, Si, V and Nb) formed in sulphate solution in the presence and absence of chloride ions. All ternary alloying elements i ncrease the pitting potential compared to the corresponding binary all oy. Films formed in chloride containing sulphate solution contain both electrolyte anions. Scanning Auger microscopy reveals that for a two phase system such as Fe-25Cr-11Nb, the dendritic phase is enriched wit h chromium, while essentially all of the niobium is located in the int erdendritic eutectic.