Abstract
The oxidation of TD NiC (Ni-20Cr-2 vol pct ThO2) has been studied at temperatures between 900° and 1200°C. Chromium is selectively oxidized in TD NiC and the parabolic rate constants for the growth of the resulting Cr2O3 layer are about an order of magnitude lower than those for the growth of Cr2O3 on a simple Ni-Cr alloy. The oxidation rate of TD NiC is initially controlled by the interplay of diffusion through the Cr2O3 scale and the formation of gaseous CrO3 but after extended periods of oxidation the rate corresponds to that of the vaporization process. Comparison of results obtained for the oxidation of TD NiC to those for Ni-Cr alloys indicates that the ThO2 dispersion inTD NiC improves the oxidation properties of this alloy by promoting the selective oxidation of chromium and decreasing the growth rate of the Cr2O3 scale.
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