Oxidation behaviour of yttria dispersion strengthened Fe40Al alloy foils

The oxidation behaviour of oxide dispersion strengthened (ODS) Fe40Al–1Y2O3 foils of about 300 μm thickness was investigated in air at 1100 °C for up to about 300 h exposure. Additional information on the oxidation process and dimensional stability of oxidised specimens was obtained during isochronal tests (45 h) in the temperature range of 1025–1125 °C. For comparative purposes, foils of a Fe40Al intermetallic alloy without yttria and of the alloy PM 2000, a commercial alumina forming Fe-base alloy, were also investigated. Oxidation kinetics reveal that the scale growth rate of the intermetallic alloys are considerably lower than for PM 2000, which is a consequence of the development of a chemically purer alumina scale. Comparative analysis of the oxidation kinetics of the intermetallic alloys indicates a slightly lower oxidation rate for the material having 1% yttria. A major characteristic of the oxidation behaviour of the Fe40Al–1Y2O3 is the tendency for partial scale spallation after relatively short exposures. This has been attributed to the elevated residual compressive stresses induced by the difference in the thermal expansion coefficients of the alumina scale and the substrate. Changes in the area of the specimens after oxidation (up to about 3% increase) provides evidence of the relaxation by creep of the substrate induced by those residual compressive stresses existing at the scale.