Dissolution and passivation of aluminide coatings on model and Ni-based superalloy

Electrolytic dissolution of aluminide coatings on model (pure Ni, Ni20Cr) and Rene 125 Ni-based superalloy was conducted by alternated cathodic and anodic polarizations. The pure nickel aluminide dissolved homogeneously. In contrast, the inhomogeneity of dissolution increased with the incorporation of Cr in the coating. The coatings were however uniformly dissolved when the cathodic step was eliminated. XPS and TEM demonstrate that the occurrence of a passive layer containing Cr and Al oxy-hydroxides blocked dissolution.