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Effect of a high hafnium content on the high temperature oxidation of chromium-rich cast alloys. Part 5 : Oxidation at heating of co-based alloys

Elodie Conrath, Patrice Berthod

After the nickel-based alloys and the iron-based alloys, this is here the case of the cobalt-based alloys which is examined concerning the effect of unusually high hafniumcontents on the oxidation during heating up to 1000 or 1100°C. The thermogravimetric tests were done in air for 50 hours and the obtained mass gain files exploited in their heating part.Acorrection fromthe air buoyancy variation was realized to obtain mas gain curves suitable for analyses. The studied parameters were the temperature of oxidation start, the total mass gain during heating, the instantaneous linear constant versus temperature, the linear constant representing the pre-parabolic transient oxidation, and finally the corresponding activation energies. These characteristics describing the behaviour of the alloys in oxidation during heating were all studied with regards to the contents of the alloys in carbon and in hafnium.Generally the resultswere not very clear.However interesting observationswere done, for example concerning the totalmass gain achieved during heating.