Microstructure and diffusion behavior of Co-Ni-W conversion coating for metallic interconnect of solid oxide fuel cell

To improve the oxidation resistance and electrical conductivity of the interconnects, a new Co-Ni-W alloy layer containing 5.0 at.% W electroplated on the surface of SUS 430 stainless steel and oxidized at 800°C in air for 1000 h was studied. It was confirmed that the oxide layer structure eventually evolves into six oxide layers after oxidation, namely Co3O4, CoFe2O4, NiCo2O4/CoWO4, (Co,Fe,Ni)3O4, (Cr,Fe,Co)3O4, and Cr2O3 layer by scanning electron microscope, transmission electron microscope and X-ray diffraction. The four Cr-free oxide layers completely prevented the outward diffusion of Cr. Furthermore, the Co-Ni-W coating significantly reduced the area specific resistance of sample.