An x-ray reflectivity study of β-NiAl oxidation

Early stages in the cyclic oxidation of ß-NiAl at 500°C were investigated using the technique of x-ray reflectivity. By fitting the reflectivity curves to a model function, oxide layer thickness, roughness of the oxide-gas and the oxide-substrate interfaces were obtained as a function of oxidation time. It was observed that the oxide thickness increased logarithmically with time. Comparison of the roughness of the oxide-substrate interface with that of the oxide-gas interface showed that the oxide-gas interface was rougher than the oxide-substrate interface. This is consistent with the postulated growth mechanism (outward diffusion of cations) for oxide growth during the early stages of oxidation at low temperatures in this material. Thus, x-ray reflectivity offers a convenient way of determining oxide growth rates along with the roughness of the interfaces when the oxide layer is thin; this regime cannot be easily studied with techniques that are currently being used for oxidation studies. Published by Elsevier Science Ltd.