High temperature oxidation of thin FeCrAl strips

This study concerns the oxidation behaviour between 850 and 1100 degrees C of FeCrAl thin strips. Oxidation kinetics have been continuously recorded on a thermobalance as well as discontinuously in an "industrial" furnace. Detailed observations of oxide layers have been performed in Transmission Electron Microscopy on oxidized thin foil cross-sections. Oxide morphologies are correlated with kinetics: Slow kinetics and columnar alpha alumina grains above 950 degrees C, fast kinetics and transition alumina platelets (gamma-alumina) at 850 degrees C, and 900 degrees C, followed by small alpha-alumina grains formation underneath. The weight gains in the industrial furnace displayed significant scatter and were generally greater than those measured in the thermobalance. The effect of extrinsic factors such as specimen size and shape, atmosphere, air flow conditions on the early formation of transition aluminas explains the observed differences. It appears then that in given cases parabolic constant identification from TGA recordings is difficult, or even impossible. This might contribute to explain the differences in the results presented in the literature.