Abstrait

Roles of thematrix and of the primary carbides in the general high temperature oxidation behaviour of cobalt-based superalloys. Part 2: the Co(10Ni,30Cr) matrix with chromium carbides

Albert Leroy,Alexandre Navet, Thierry Schweitzer, LionelAranda, Patrice Berthod

Most of the cast cobalt-based superalloys contain interdendritic carbides to strengthened them against mechanical solicitations at high temperature. Among the most common carbides used in this field there are the chromium carbides the formation of which does not necessitate new carbide- former elemnts since chromium is always present for oxidation and corrosion resistance purpose. Such carbides may influence the general oxidation behaviour of the whole alloy. In order to specify their contribution a cobalt alloy containing 10 wt.Ni and 30 wt.%Cr as most of cobaltbased superalloys, and 0.5 wt.%C to obtain chromium carbides in the microstructure, was studied in oxidation for the whole same thermal cycle as applied to a Co-10Ni-30Cr ternary alloy preliminarily characterized in the first part of this study. Many parameters describing the oxidation during the heating, the isothermal stage and the cooling were compared between these two alloys. There was not systematically differences but it significantly appeared that the {chromium carbides}-containing alloy oxidized faster during the heating and the isothermal stage than the carbidesfree one. In contrast, if oxide spallation occurred for the studied alloy as previously also observed for the ternary alloy, this phenomenon was delayed later as is to say to lower temperatures.