Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation

The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe–22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10 nm Ce, 640 nm Co and 10 nm Ce + 640 nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850 °C in the air with 3% H2O for 168 h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640 nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10 nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640 nm Co coating on top of the 10 nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.