Effect of surface curvature on oxidation of a MCrAlY coating

The oxidation behaviour of a high velocity oxygen fuel (HVOF) sprayed MCrAlY coating at 1150 degrees C is studied. The rough coating surface shows site-specific oxidation: the oxides in the convex regions show duplex microstructure, consisting of outer (Ni,Co)(Cr,Al)(2)O-4 and inner alpha-Al2O3; the oxides in the concave regions, however, show single-layered microstructure comprised of exclusive alpha-Al2O3. Diffusional analysis predicts that in order to form an exclusive alpha-Al2O3 scale the minimum Al concentration in the gamma-phase matrix in the convex regions must be higher than that in the concave regions. The study provides new insight into oxidation of MCrAlY coatings.