High temperature oxidation behaviour of alloys containing very high densities of carbides
Résumé
Some alloys containing both very high fractions of carbides and a high amount of chromium can potentially display a low thermal expansion and a good resistance against high temperature oxidation, simultaneously. The aim of this work is to explore the high temperature oxidation behaviour of such alloys, by studying three alloys based on nickel and one based on cobalt, all of them containing more than one weight percent of carbon to obtain very high carbides fractions and 30%wt. of chromium added to achieve a chromia-forming behaviour. The studied alloys are almost all sufficiently resistant against oxidation for this exposure duration. The parabolic constant Kp and the constant of chromia volatilization Kv for the nickel alloys do not follow a systematic law of variation versus the carbon content. However the depth of the carbide free zone clearly decreases when the carbon content increases. It is possible that the impoverishment of the matrix for very high fractions of chromium carbides (which then contain a great part of chromium), can lead to local losses of the chromia-forming behaviour. In the case of the cobalt alloy the presence of tantalum obviously leads to fast mass gain kinetics but delays catastrophic oxidation.
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