Composite Cu-LaFeO3 Coating on High Cr Ferritic Stainless Steels for IT-SOFC Interconnects

A molten carbonate dip-coating passivation method has been applied in this work to produce novel copper-LaFeO3 perovskite composite conversion coatings on a commercial 18Cr ferritic stainless steel. The passivation treatment promotes the formation of a multi-layer conversion coating consisting of a dense perovskite layer grown onto a spinel oxide sublayer and characterized by the presence of copper metal particles embedded in the perovskite grains. A relation between copper addition to the molten salt bath and optimal conversion conditions is observed, with higher copper concentration resulting in accelerated passivation kinetics. When exposed to short-term oxidation experiments in air at 700°C, the perovskite layer exhibits remarkable stability, while copper gets oxidized and diffuses in the spinel sublayer. The coating is found also to act as efficient barrier to the outward diffusion of chromium, being the chromium largely confined to the steel-coating interface.