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

摘要

After having presented the as-cast microstructures of two complex carbide-strengthened cast cobalt-based alloys replicated with a fine microstructure in laboratory by melting 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℃ and 1150℃ - 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℃ but especially at 1150℃, 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℃: the loss of the chromium-tungsten carbides. The latter phenomenon induced a decrease in room temperature hardness.