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Poster De Conférence Année : 2017

Microstructures and high temperature properties of refractory alloys designed to be TiC-reinforced

Mira Khair
  • Fonction : Auteur
Floriane Allegre
  • Fonction : Auteur
Estelle Kretz
  • Fonction : Auteur
Patrice Berthod

Résumé

Some polycrystalline superalloys elaborated by classical foundry can be very refractory and bring unexpectedl y high properties at high temperature. This is for instance the case of some cobalt-based alloys strengthened by tantalum carbides or hafnium carbides. Cast alloys based on Ni or Co, and even Fe, and containing other types of MC carbides may be also envisaged for high temperature applications. In this study this is the titanium carbide phase which is investigated. Several Ni-based, Co-based and Fe-based alloys of the {M-25Cr-xC-yTi}-type (x=0.25 or 0.50, y=1 or 2, in wt.%) were elaborated by casting using a high frequency induction furnace under pure argon. Metallographic samples allowed the characterization of their microstructures by electron microscopy and energy dispersion spectrometry. Especially prepared samples were destined to DTA control of the melting range, to {1200°C, 20MPa}-flexural creep tests and to oxidation in synthetic air at 1200°C, in order to start exploring the mechanical and chemical resistances of such alloys at elevated temperatures. Titanium carbides, which are of the MC type as TaC more commonly encountered in superalloys, may be obtained at solidification in chromium-rich cast alloys. However this depends on the base element. In nickelbased alloys the titanium carbides seem being less stable than chromium carbides. Indeed, CrxCy crystallize at solidification rather than TiC, and during high temperature isothermal exposures the rare titanium carbides which precipitated among the numerous chromium carbides, completelydisappear. This is totally the contrary in chromium-rich cobalt-based and iron-based alloys: the TiC carbides were successfully obtained and remain stable during long high temperature exposure. They were obtained as scripts-like eutectic carbides imbricated with matrix in the interdendritic spaces. Associated to an intrinsic mechanically resistant cobalt-based matrix they allowed the studied cobalt-alloys demonstrating interesting creep resistance. Because of the too low strength of the ferritic matrix of the iron-based alloys, the creep behaviour of these ones did not benefit from the TiC carbides. The nickel-based alloys, combining – it is true – a muchweak nickel-based matrix, and interdendritic chromium carbides, rapidly deformed and came in touch with the apparatus basis after only about 25 hours. In contrast the oxidation kinetics of the Ni-based and Fe-based alloys were much lower than the Co-based alloys, this respecting the classical hierarchybetween the three families.
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hal-03256064 , version 1 (10-06-2021)

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  • HAL Id : hal-03256064 , version 1

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Mira Khair, Floriane Allegre, Estelle Kretz, Patrice Berthod. Microstructures and high temperature properties of refractory alloys designed to be TiC-reinforced. Asian Advanced Materials Congress 2017, Mar 2017, Diamond Princess, Singapore. ⟨hal-03256064⟩
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