Factors affecting the oxidation behaviour of thin Fe-Cr-Al foils. Part II: The effect of alloying elements: Overdoping

The oxidation behaviour of iron-chromium-aluminium alloys containing 7 mass-% aluminium, additions of silicon and reactive elements (Hf, Y, Ti, Ce, La, Zr) was investigated at temperatures ranging between 900 and 1300°C. It was found that a significant increase in the oxidation rate and in the depth of internal oxidation (so-called “overdoping”) occurs above a critical concentration of reactive elements. The critical upper limit of each reactive elements depends on the aluminium concentration, on the kind of the respective reactive element and on the type and amount of other reactive elements. Alloys containing yttrium are only subject to internal oxidation at yttrium concentrations of 0.08 mass-% and more. The susceptibility to “overdoping” is significantly increased by additions of zirconium and titanium to yttrium-containing alloys. Additions of hafnium, on the other hand, decrease the oxidation rate and the susceptibility to overdoping.