Steam oxidation of aluminide coatings under high pressure and for long exposures

B2-FeAl-based aluminide coatings were elaborated on P92 ferritic-martensitic steels by slurry. A thin protective α-Al2O3 oxide layer was stable until 5000 h at 650 °C under flowing steam at 1 bar. At 300 bar and stagnant steam conditions, the morphology of α-Al2O3 changed markedly. Iron oxide clusters started to appear at the surface of the scale after 5000 h of exposure and kept on growing till 10,000 h. It appears that pressure increased the outward diffusion of Fe through the coating and through the oxide scale and fostered the propagation of the tensile cracks of the coating.