Evidence for Cr-carbide formation at the scale/metal interface during oxidation of FeCrAl alloys

Two FeCrAlY alloys with different carbon contents (90 and 500 ppm, respectively) were investigated in respect of their oxidation behaviour at 1200 °C in air. Both alloys exhibited formation of grain boundary Cr-carbides after 1200 °C exposure, whereas the high-carbon content alloy additionally showed carbide formation at the interface between alloy and alumina surface scale. The extent of the carbides formed at both this interface and the alloy grain boundaries was dependent on the cooling rates of the oxidized samples. The presence of the carbides may decrease the adherence of the oxide scale to the metallic substrate and explain the decreased time to breakaway oxidation of the high-carbon content alloy.