In the present work the effects of single or combined minor additions of Zr, Hf, Ti and C on the oxidation behaviour of Y-containing, FeCrAl alloys have been studied. For this purpose high-purity, model alloys with single or multiple minor alloying additions were used. The results of long term discontinuous oxidation tests and detailed kinetics studies using thermogravimetry were complemented with extensive microstructural characterisation of the formed alumina scales using SEM and STEM. Hence, the oxidation kinetics and scale spallation rates and failure modes were correlated with the oxide composition and microstructure. The results demonstrate that the frequently reported positive effect of Zr, Hf and Ti on the lifetime oxidation behaviour of FeCrAl alloys can only be fully exploited if the concentrations of the above elements are carefully adjusted and the interaction with typical alloy impurities, such as carbon, is considered.

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The oxidation behaviour of 30 mm and 50 mm thick Aluchrom YHf and 50 mm thick Kanthal AF foils have been examined during discontinuous exposure (100 h cycles) to laboratory air at 800, 850, 900 and 950uC. Oxidation was continued out to 3000 h or until chemical failure ensued, whichever was the shorter. Resulting observations include two oxidation temperature domains, a two-stage oxidation process leading to a duplex (transitional-a) alumina scale and ultimately, a two-stage chemical failure process of the oxide scale leading to breakaway/non-protective attack. To unravel the underlying mechanisms involved, the scales were examined by a range of microscopy and analytical techniques, including optical and scanning electron microscopy (SEM), electron microprobe analysis (EPMA), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD).

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