Use of thermogravimetry and thermodynamic calculations for specifying chromium diffusion occurring in alloys containing chromium carbides during high temperature oxidation
Résumé
The chromium diffusion is of great importance for the high temperature oxidation behavior of the chromia-forming carbides-strengthened superalloys. These ones are rich in this element for insuring their resistance against hot corrosion by constitute and maintain a continuous external scale of chromia protecting them. Knowing the chromium diffusion in such alloys is thus very useful for predicting the sustainability of their chromia-forming behavior. Since this Cr diffusion occurs through the external part of the alloy already affected by the previous steps of oxidation (decarburized subsurface) it is more accurate to specify this diffusion during the oxidation process itself. This was successfully carried out in this work in the case of a model chromia-forming nickel-based alloy containing chromium carbides, Ni(bal.)-25Cr-0.5C (in wt.%), by combining the mass gain kinetic by oxidation specified by real-time thermogravimetry and the post-mortem determination of the Cr concentration profiles in subsurface. The values of DCr thus obtained for 1000, 1050 and 1100°C in the alloy subsurface are consistent with the values obtained in earlier works for similar alloy's chemical compositions.
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