Isothermal oxidation of Ni3Al before and after microcrystallizing at 1 000 degrees C in O-2 has been studied using thermobalance method. It is found that the resistance to oxidation of Ni3Al is greatly improved after microcrystallizing. The oxidation rate of microcrystalline Ni3Al markedly decreases. The oxidation kinetics of microcrystalline Ni3Al is much lower than that of the power law pro posed by Wagner. This work focuses on the deviation of kinetics. In the Wagner theory, It was assumed that oxide film grows by lattice diffusion. But the grain of oxide film on microcrystalline Ni3Al is microcrystalline and the density of grain boundary greatly increases. Therefore, short-range diffusion is much more than lattice diffusion. Considering the effects of defects on oxidation kinetics and the grow kinetics of oxide grain, the oxidation kinetics of microcrystalline Ni3Al is derived to obey the forth power law, ie, chi(4) = k(p)t. The experimental results agree with the values calculated by the formula.
