Composition, structure and protective properties of alumina scales on iron-based oxide dispersion strengthened alloys

The oxidation behaviour of a number of iron/chromium/aluminium based oxide dispersion strengthened (ODS) alloys of the type MA 956 was investigated at temperatures between 900 and 1200°C. Apart from studies on long-time cyclic oxidation resistance, the main emphasis was placed on the effect of alloy yttria content on scale composition and structure as a function of time and temperature. The detailed scale analyses were made by using Rutherford backscattering analysis in addition to electron-optical methods. It was found that during short-term oxidation the scale growth rate at 900°C showed a deviation from the Arrhenius-type temperature dependence observed at higher temperatures. This could be attributed to formation of a metastable alumina modification in the initial stages of oxidation at 900°C. Studies of a series of alloys with variations of alloy yttria content in the range 0.17−0.7% showed an increase in the oxide growth rate with increasing yttria content. The reason for this technologically Import...