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

Surfaces of Ni, Cr and Ni-based superalloys were coated with nanocryst alline CeO2 dispersions derived from sol-gel. At high temperatures, Ce O2 particles are incorporated into the growing NiO acid Cr2O3, where t hey act as a source of Ce+4 ions in oxide grain boundaries. It is sugg ested that the Ce+4 ions block outward diffusion of metal ions along o xide grain boundaries, significantly inhibiting oxide growth. An analy sis of the oxidation kinetics is presented that supports this hypothes is. Optimizing oxide microstructure to improve its protective properti es al high temperatures is discussed.