Thermodynamic study of the mushy zone of cobalt-based superalloys. Part 2: Case of a high carbon alloy

Author(s): Patrice Berthod, Elodie Conrath

After having controlled the reliability of the thermodynamic modelization tool in the first part of this work, thermodynamic calculations were here used again, this time to try finding the value of the high temperature known by a piece made of a cobalt-based superalloy which seemingly partially melted. For that the chemical compositions of the matrix and of the molten then re-solidified areas were measured by EnergyDispersion Spectrometry, as well as the surface fractions. Thermodynamic calculations performed fromthe global chemical composition of the whole alloy also controlled by EDS allowed, by comparison between the calculated results and the metallographic ones, to assess the temperature at which the alloy was exposed. A very good agreement was found between the different temperatures suggested by the fractions of re-solidified molten areas and of the tantalum carbides having remained solid during H.T. exposure, by the chemical compositions of the matrix and of the re-solidified molten areas, with however some exceptions. Thus, the value determined for the exposure temperature appeared rather reliable, and the thermodynamic calculation package efficient as an expertise tool for such post-mortem determination.

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