STRESSES IN NIO, CR2O3 AND AL2O3 OXIDE SCALES

The protective character of oxide scales developed at high temperature on metallic alloys strongly depends on the adherence of the scales which must be related to the stress level in the scales. Thus, after a review of the origins of the stresses in such scales, the methods actually used for determining the stresses either at room temperature or during the oxidation sequences are briefly mentioned. Results concerning NiO, Cr2O, and Al2O3 scales are presented. These results are discussed in relation with the stress origin and they are compared with results obtained by theoretical modelling. It is suggested that growth stresses are particularly related to the scale growth mechanism, and that they are of minor importance compared with thermal stresses so that, for the systems considered, the adherence loss mainly results from the thermal stresses and/or from the poor quality of the scale-metallic substrate interface due to the defect concentration at this interface.