Abstract
The influence of composition on the oxidation of NiAl and CoAl has been investigated. Oxidation kinetics have been studied. using a microbalance system which allows the weight gain of the oxidizing specimens to be monitored continuously, to an accuracy of ± 2 μg. Auger electron spectroscopy has been applied to the analysis of the oxidation products. Both NiAl and CoAl show a minimum in the variation of oxidation rate with composition, these minima being at about 58 at.-%Ni and 50 at.-% Co for NiAl and CoAl, respectively, when oxidized in pure oxygen at 1173 K. The dependence of oxidation rates and products on aluminium content is discussed in terms of aluminium activity and alloy interdiffusion coefficients. It is shown that, although the observed results agree qualitatively with theoretical considerations, the oxidation rate cannot be predicted quantitatively from fundamental data because of the complex variation and interrelation of the relevant parameters.
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