The effect of micro-alloying with Zr and Nb on the oxidation behavior of Fe3Al and FeAl alloys

Iron aluminides containing 27, 33 and 39 at.% aluminum with low amounts (<0.5 at.%) of Zr, Nb, C and B have been investigated with respect to the interplay between microstructural evolution and oxidation behavior. Zirconium and Niobium have a low solubility in iron aluminides and form precipitates, e.g. Laves phases, carbides or borides. The isothermal oxidation behavior has been studied in laboratory air at 750, 900 and 1050 °C with respect to kinetic aspects and oxide layer growth. Mass change was recorded in intervals weighing the samples outside the furnace. The evolution of microstructure and layer growth has been analyzed utilizing SEM (EDX), EPMA, EBSD, XRD and OM. Generally, as expected, an outstanding oxidation resistance of all investigated alloys was observed due to the formation of Al2O3 scales with a very slow growth rate. However, in contrast to binary iron aluminides in the same composition range, the mass gain with time increases with increasing aluminum content. The findings are discussed in terms of scale properties and internal oxidation.