Abstrakt
Abstract: The cyclic oxidation behaviour of Fe-26Al-3Nb, Fe-27Al-5Nb and Fe-26Al-5Nb-1.4C (in at%) was investigated at 900°C. Chemical and phase analyses of the scale and oxide protrusions were conducted using light optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction.
The oxidation resistance of the tested alloys was determined using fractal dimension, and the results were compared with Fe-26Al-0.3Zr, Fe-26Al-1Zr (at%) and EN X5CrNi18-10 steel. The oxidation kinetics of Fe-26Al-3Nb and Fe-27Al-5Nb follow the parabolic rate law.
Oxidation ingress into the alloys was observed due to the preferential oxidation of niobium-rich precipitates. Therefore, the oxidation rate of tested alloys increased with increasing amounts of particles of Laves phase (Fe, Al)2Nb and NbC.
The niobium carbides oxidised more readily than the particles of Laves phase (Fe, Al)2Nb. The cyclic oxidation of Fe-Al-Nb and Fe-Al-Nb-C alloys at 900°C led to the formation of oxide scales composed of Al2O3, Fe2O3 and AlNbO4 (or non-stoichiometric AlNbO4).
Graphical Abstract: [Figure not available: see fulltext.]