Self Healing of Precoated AISI 441 for Solid Oxide Fuel Cell Interconnects

Sandvik Materials Technology develops nanocoatings for SOFC stainless steel interconnects. The self healing properties of cerium cobalt coated AISI441 (EN 1.4509) have been studied. A selectively coated sample was oxidized in air at 800°C for a total of 504 hours. A FIB trench, milled on the uncoated surface, was used as a reference point for the coated border. A second FIB trench, made after oxidation, revealed that the oxide formed on the uncoated part adjacent to the coated area contained both cobalt and cerium. Cerium was detected with EDS in the surface oxide of the uncoated area as far as 10 mm away from the coated edge, cobalt had diffused even further. These findings are encouraging since they suggests that cracks introduce in the coating during stamping and/or forming, which are usually in the 1-3 mm range, are likely to self heal (i.e. become enclosed by an upper Co, Mn, Cr-spinel)  upon oxidation.