Oxidation of Fe-Al Alloys (5-40 at.% Al) at 700 and 900 °C

Fe-Al alloys with Al contents between 5 and 40 at.% Al were oxidised for 1000 h in synthetic air at 700 and 900 °C to determine their oxidation behaviour. The minimum Al content which is necessary for the formation of protective Al2O3 scales decreases with increasing temperature from about 17 at.% Al at 700 °C to about 12 at.% Al at 900 °C. Established parabolic rate constants for the steady state growth of Al2O3 indicate formation of γ-Al2O3 at 700 °C while at 900 °C α-Al2O3 + Θ-Al2O3 scales form. At lower Al contents scales are predominantly formed by Fe2O3 as revealed by GI-XRD. It is also found that the oxidation behaviour is independent of the crystallographic order of the alloys, i.e. whether they are disordered A2 or ordered B2.