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Isothermal oxidation of sputtered Ni-5Cr-5Al (at%) nanocrystalline coatings were investigated at 900 degrees C and 1000 degrees C in air. Both of them showed low oxidation rates. The oxidation kinetics of sputtered Ni-5Cr-5Al coating was much slower than that predicted by parabolic kinetics of scale growth by lattice or volume diffusion. The much smaller oxide grains could be formed on sputtered coating thereby higher density of grain boundary could be existed in the oxide scale than that formed on cast alloy. Taking the short circuit diffusion through grain boundaries into account, an oxidation kinetic with fourth power law was derived. The excellent results in agreement with the experimental data were obtained. (C)1999 Acta Metallurgica Inc.