CONTROLLING GRAIN-BOUNDARY DIFFUSION IN OXIDE-FILMS BY REACTIVE ELEMENT ADDITION

Surfaces of Ni, Cr and Ni-based superalloys were coated with nanocrystalline CeO2 dispersions derived from sol-gel. At high temperatures, CeO2 particles are incorporated into the growing NiO acid Cr2O3, where they act as a source of Ce+4 ions in oxide grain boundaries. It is suggested that the Ce+4 ions block outward diffusion of metal ions along oxide grain boundaries, significantly inhibiting oxide growth. An analysis of the oxidation kinetics is presented that supports this hypothesis. Optimizing oxide microstructure to improve its protective properties al high temperatures is discussed.