The oxidation behavior of Fe-Al alloys

Iron-aluminum alloys range from intermetallics like FeAl and Fe ₃Al to ferritic Fe-Al and their oxidation behaviors vary significantly. The intermetallic phases have large coefficients of thermal expansion (CTE) which results in scale spallation. Alloys below 24at.%Al are ferritic with much lower CTEs, comparable to FeCrAl, and show much better scale adhesion. Unlike the intermetallic phases which show maximum lifetime with Hf doping, ferritic alloys show longer lifetimes with Y additions. However, their lifetimes are limited because of their low Al content and relatively high critical Al content at breakaway oxidation of 10at.%. Modeling the lifetime of ferritic Fe-Al alloys is complicated by the presence of Al gradients which leads to unexpected failure behavior with respect to Al content and specimen thickness.