High temperature oxidation of Co-W electroplated type 430 stainless steel for the interconnect of solid oxide fuel cells

Cobalt-tungsten alloy layer containing 2.4 at% W was electroplated on type 430 stainless steel (Fe-16 mass% Cr), and it was subjected to high-temperature oxidation at 800 °C in Air-3 vol% H2O atmosphere for 1000 h. A five-layered oxide of Co3O4, FeCo2O4, CoWO4, (Co,Fe,Cr)3O4, and Cr2O3 formed within 1 h, and the structure retained up to 1000 h. The outward diffusion of Cr3+ was effectively prevented by the CoWO4 layer. In the oxide, Co and W exist as divalent and hexavalent ions respectively, and there is no trivalent cation sites or trivalent cation vacancy through which Cr3+ diffuses.