High temperature environmental interactions in carbon-alloyed iron aluminide of low Al content

High temperature material–environmental interactions (oxidation and decarburization) have been studied in a carbon-alloyed iron aluminide of composition Fe–8.5%Al–0.42%C (wt.%). Bulky Fe3AlCX carbides were uniformly distributed in a matrix of Fe3Al. Samples were exposed at 923, 973, 1023, and 1073 K in laboratory air for different lengths of time and their surface scales were characterized. The oxidation rate decreased beyond 973 K, which has been explained by a change in the nature of the surface scale. Analysis of the decarburized microstructures revealed that the carbides decomposed into finer carbides, dissolved in the matrix and carbon diffused out to the surface. The mechanism of decarburization appears to be similar to that in steels.