COMPARATIVE STUDY ON THE ISOTHERMAL AND CYCLIC OXIDATION BEHAVIOUR OF FeCrAl ALLOYS EXPOSED TO ARGON AND STEAM ENVIRONMENTS AT HIGH TEMPERATURE

Abstract

The isothermal and cyclic oxidation behavior of Fe-21Cr-5Al alloys has been studied in steam at 1000°C using a steam rig testing furnace and post-exposure microstructural surface analysis. The results showed that the isothermal exposure exhibited a uniform thick alumina scale (approximately 2 µm) on the surface, and the scale was free of other oxides. The cyclic oxidation showed serious oxide penetration around the interfaces, and the oxide penetration rate depended on cycle frequency. The alumina oxide formed during cyclic exposure underwent thermal stress, and this stress may be relieved by fracture of the scale (or plastic deformation in the alloy). The presence of other alloying elements (mixed) oxides (Cr, Fe) was observed around the spalled alumina oxides on the cross-section of samples. All exposure conditions showed outward diffusion of Al to the surface, forming a protective solid-state diffusion barrier and reducing the reaction between the alloy and the surrounding environment.