The high temperature oxidation behaviour of an ODS FeAl alloy

The oxidation behaviour of an oxide dispersion-strengthened (ODS) FeAl intermetallic, microalloyed with Zr and B and strengthened by a fine dispersion of Y 2O 3, is investigated at 1100°C for exposures of up to 200 h. The results show that a pure alumina scale is formed irrespective of the exposure time. The oxidation rate is far inferior to that found on PM 2000, a commercial alumina forming ODS ferritic superalloy. Limited scale spallation is observed in the intermetallic alloy from the early stages of oxidation. Scale failure, which is shown to occur during the cooling stage after oxidation and not at the high temperature of oxidation itself, results from the high compressive residual stresses in the scale induced by the misfit in the thermal expansion coefficients of the scale and the substrate. Failure of the scale may be supressed by using a very low cooling rate after oxidation.