Slurry iron aluminide coatings are very resistant to steam oxidation at 600-650º C. These
coatings can be used to protect new generation Ultra Super Critical (USC) steam power plant
ferritic/martensitic steel components. The microstructure of the initially deposited coating changes
as a function of time, mainly due to coating-substrate interdiffusion, going from mostly Fe2Al5 to
FeAl, causing the precipitation of AlN in those substrates containing a minimum content of N and
moreover, developing Kirkendall porosity at the coating-substrate interface. Steam oxidation at 650º
C causes the formation of a protective thin layer of hexagonal χ-Al2O3 phase along with some α-
and γ-Al2O3 after the first few hours of exposure. However, despite the relatively low temperature,
and after several thousands hours the protective layer was mostly composed of α-Al2O3. A study of
the evolution of the microstructure of slurry aluminide coatings deposited on P92 and exposed to
steam at 650º C has been carried out by scanning and transmission electron microscopy and X ray
diffraction.