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Poster De Conférence Année : 2013

Microstructure evolution and oxidation behavior at high temperature of cobalt-based superalloys strengthened by hafnium carbides

Patrice Berthod

Résumé

Cobalt-based superalloys elaborated by foundry are often reinforced by carbides, which are generally of different types. The most common among them are chromium carbides and tantalum carbides. Unfortunately the presence of the formers generally induces for the alloy a decrease in solidus temperature while the later tend to become fragmented during high temperature exposures, with consequently a loss of mechanical resistance at high temperature. Other types of carbides can be considered to strengthen such superalloys, for example hafnium carbides. In this work three HfC-reinforced chromium-rich cobalt-based alloys, Co(bal.)-25Cr-xC-yHf with (x; y)=(0.25; 3.72), (0.50; 3.72) and (0.50; 7.44) (weight contents chosen for having 1/1 and 2/1 atomic ratios between C and Hf), were elaborated by foundry and exposed at 1200°C for 50 hours to characterize their behaviours in terms of microstructure stability and of high temperature oxidation. In these fields they were compared with two Hf-free Co-25Cr-0.25&0.50C alloys subjected to the same tests. Two of the three HfC-strengthened Co-based alloys studied in this work were thus successfully obtained with a dendritic matrix and an interdendritic carbides network of script eutectic HfC, thanks to an atomic ratio Hf/C equal to 1. The obtained HfC carbides were obviously slower fragmented than what it was generally observed for TaC when they are present in such quantities in other cobalt-based alloys. These observations let think that such alloys may owning high mechanical properties at high temperature and notably efficient resistance against creep-deformation. In contrast their high temperature oxidation behaviour was not so good since no of them showed a chromia-forming behaviour despite their 25wt.%Cr and severe oxide spallation. Fortunately this may be improved by modifying their bulk chemical composition (e.g. increase in Cr, rare earth additions), the one of their sub-surface (e.g. by enriching it in Cr by pack-cementation) or by depositing a protective coating.
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Dates et versions

hal-03609889 , version 1 (16-03-2022)

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  • HAL Id : hal-03609889 , version 1

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Patrice Berthod, Elodie Conrath. Microstructure evolution and oxidation behavior at high temperature of cobalt-based superalloys strengthened by hafnium carbides. Beyond Nickel-Based Superalloys, May 2013, Bad Berneck, Germany. ⟨hal-03609889⟩
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