Influence of the yttria content on the oxidation behaviour of the intermetallic Fe40Al Alloy

The oxidation behaviour of Fe40Al strengthened by a fine dispersion of either 0.5 or 1 wt.% Y2O3 has been examined in air at 900 and 1100 °C. Long exposure times of up to 1000 h were used. At the lowest temperature, the material having 1% yttria develops from the earliest stage of oxidation an α-alumina scale on the surface, leading to a more protective and thinner scale. Oxidation kinetics of the material with 0.5% yttria, however, is controlled by the formation of metastable θ-alumina. Volume reduction associated to its transformation during oxidation to stable α-alumina accounts for the significant scale spallation after about 300 h exposure. At 1100 °C, the oxidation reaction is controlled by the formation of an α-alumina scale, the thickness of the scale being larger for the material having 1% yttria. The larger thickness could result from the smaller grain size of the alumina scale. The large mismatch of the thermal expansion coefficients between the alumina and the intermetallic alloy accounts for the scale spallation observed in both alloys at this temperature.