We have studied microdefects and interfaces of AI203 films on iron and nickel aluminide substrates using variable-energy positron lifetime spectroscopy. Di-vacancies, vacancy clusters, and microvoids were observed in the oxide scales. Their sizes and distributions were determined by the nature of the process used to synthesize the alumina film. and influenced by the composition of the alloy substrates. For oxide-iron aluminide interfaces, positron lifetimes are longer than those for the alumina layer itself, suggesting a greater defect concentration at such sites.#1997 American Institute of Physics. S0003-6951(97)02547-3
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