Formation of perovskite type phases during the high temperature oxidation of stainless steels coated with reactive element oxides

The beneficial effects of reactive elements (RE) on the high temperature (HT) oxidation behavior of stainless steels have previously been attributed to the formation of perovskite compounds on oxide grain boundaries. In order to verify the ability of Cr2O3 to form perovskite compounds with reactive element oxides RE2O3 (RE=La, Nd, Sm, Gd, Yb, Y), mixtures of Cr2O3 and RE2O3 powders were oxidized at 1000 degreesC in air, and characterized by X-ray diffraction. Results were compared to those obtained on RE2O3-coated Fe-30Cr samples (RE=Y, Nd, Sin, Yb) oxidized at 1000 degreesC under the same conditions. It was found that the most efficient reactive element oxide, Y2O3, was not this which was completely converted into perovskite structure. So, it is assumed that it is not the reaction rate of the perovskite formation, or the ability of the RE oxide to form a perovskite structure, but rather the intrinsic properties of the perovskite, which is the origin of the RE effect. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.