Factors affecting the oxidation behaviour of thin Fe-Cu-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 degrees C. It was found that a significant increase in the oxidation rate and in th e depth of internal oxidation (so-called "overdoping") occurs above a criti cal concentration of reactive elements. The critical upper limit of each re active elements depends on the aluminium concentration, on the kind of the respective reactive element and on the type and amount of other reactive el ements. Alloys containing yttrium are only subject to internal oxidation at yttrium concentrations of 0.08 mass-% and more. The susceptibility to "ove rdoping" is significantly increased by additions of zirconium and titanium to yttrium-containing alloys. Additions of hafnium, on the other hand, decr ease the oxidation rate and the susceptibility to overdoping.