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Behaviour at high temperature of two cobalt-based superalloys reinforced by carbides. Part 1: Case of a high carbon {Co-1C-21.5Cr-4.5Ta-9W}-based superalloy

Pierre-Yves Girardin, Adrien Frigerio, Patrice Berthod

After having presented the as-castmicrostructures of two complex carbidestrengthened cast cobalt-based alloys replicated with a fine microstructure in laboratory bymelting of pure elements, this work, presented in two parts, aims specifying the high temperature oxidation and high temperature microstructural behaviours at two levels of temperature - 1050°C and 1150°C – and for two durations - 66 hours and 146 hours – of these two alloys. In this first part it the case of the Co(bal.)-1C-21.5Cr-4.5Ta-9W(wt.%)which is under consideration. It appeared here that this alloy did not behave very well in oxidation, already at 1050°C but especially at 1150°C, temperature at which catastrophic oxidation occurred early.At the lowest tested temperature the carbide population did not significantly evolve while a more important difference appeared at 1150°C: the loss of the chromium-tungsten carbides. The latter phenomenon induced a decrease in room temperature hardness.