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Effect of a high hafniumcontent on the high temperature oxidation of chromium-rich cast alloys. Part 1:Oxidation at heating of fe-based alloys

Elodie Conrath, Patrice Berthod

Hafnium is recognized to enhance the resistance of alloys against high temperature oxidation. The effect of this element, generally added in small quantities (typically 1wt.% and less), is not known when it is present with rather high contents. In this work, cast chromium-rich iron-based alloys containing four times the usual content were tested in oxidation at 1000 and 1100°C, to complete existing works earlier realized at 1200°C. The thermogravimetric tests were done in dry synthetic air for 46 hours and the obtainedmass gain files exploited in their heating part.After correction from air buoyancy variation, the curves of mass gain versus temperature were analysed. This aimed to specify the temperature of oxidation start, the total mass gain during heating, the instantaneous linear constant versus temperature aswell as the linear constant representing the transient oxidation preceding the parabolic regime, and the corresponding activation energies. These characteristics describing the rate of oxidation during heating were all studied versus the contents of the alloys in carbon and in hafnium. It was attempted to extract the roles of these two elements on the different kinetic parameters of oxidation-induced mass gain during heating.