Oxidation of Fe-22Cr Coated with Co304: Microstructure Evolution and the Effect of Growth Stresses 

The oxidation behavior of a commercially available Fe-22Cr alloy coated with a Co 3O 4 layer by metal organic-chemical vapor deposition was investigated in air with 1% H 2O at 1,173 K and compared to the oxidation behavior of the non-coated alloy. The oxide morphology was examined with X-ray diffraction, electron microscopy, and energy dispersive X-ray spectroscopy. Cr 2O 3 developed in between the Co 3O 4 coating and the alloy, while alloying elements of the substrate were incorporated into the coating. Particular attention was devoted to possible sources of growth stresses and the effect of the growth stresses on microstructure evolution in the scales that developed on the non-coated and the coated Fe-22Cr alloy. Microstructural features suggested that scale spallation on coated Fe-22Cr occurred as a result of superimposing thermal stresses during cooling onto the growth stresses, that had developed during oxidation. © Springer Science+Business Media, LLC 2007.