Oxidation resistance of Fe–25Al–2Ta (at.%) in air

The high-temperature oxidation behaviour of Fe–25Al–2Ta (in at.%) has been investigated between 600 and 1000 °C using thermogravimetric analysis (TGA) in synthetic air. After oxidation for 1000 h the scales were analysed by light optical microscopy (LOM), grazing incidents X-ray diffraction (GI-XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Between 600 and 800 °C thin adherent oxide scales grew according to a parabolic rate law. At 900 °C parabolic growth was observed for several hundred hours, interrupted by sudden mass gains which are probably caused by cracking of the scales, while at 1000 °C no protective scales formed. The scales are predominantly formed by Al2O3 and minor amounts of Fe2O3. While scales formed between 600 and 800 °C are still adherent after cooling to room temperature, scales formed at higher temperatures spalled during/after cooling, possibly because the Laves phase Fe2Ta formed on the sample surfaces underneath the oxide scales. Parabolic rate constants kp show that compared to other Fe–Al alloys addition of 2 at.% Ta has no detrimental effect to the excellent oxidation resistance in air between 600 and 800 °C.