Effect Of Ni Coating Thickness On High Temperature Oxidation Behavior Of Coated Stainless Steel

In today’s society,mankind is facing severe energy crisis and environmental problems.Solid oxide fuel cell(SOFC),as an energy conversion device that can directly convert the chemical energy of fuel into electrical energy,will have broad application prospects.As one of the key components of SOFC,the connector has the function of connecting single cells,separating the cathode and anode atmospheres and conducting current.Through the development of anode support and electrolyte thin film technology,the operating temperature of SOFC is reduced to 600～800℃,so that some metal materials with high temperature resistance can be used as connectors.Ferritic stainless steel(FSS)has become a research hotspot in this field due to its low cost,a coefficient of thermal expansion(CTE)that matches other battery components,and acceptable conductivity.However,the stainless steel connector has insufficient oxidation resistance and cathode Cr poisoning during long-term work.At present,the most effective way to solve these problems is to prepare a protective coating on the surface of stainless steel.In this paper,Ni coatings with different thicknesses are prepared on the surface of SUS430 stainless steel by DC magnetron sputtering technology,and converted into NiO coatings by high temperature heat.The initial and long-term oxidation behavior of Ni-coated stainless steeL under SOFC cathode working conditions(800℃ in air)are studied,and the influence of the thickness of the Ni coating on the formation and growth of the Cr2O3 layer and the inter-diffusion of elements between the substrate and the coating.Finally,the conductivity of the oxide film on the sample surface was tested.The main results obtained are as follows:The initial oxidation results of the sputtered 1 h-Ni coating show that Fe preferentially diffuses outward along the columnar grain boundaries,and a small amount of Ni diffuses into the matrix to form a NiFe phase.Cr began to diffuse to the interface between the substrate and the coating after 10 minutes of oxidation,and a continuous Cr2O3 layer was formed after 30 minutes of oxidation.After long-term oxidation,the surface of the sample has a double-layer oxide structure,the outermost layer is NiO layer,the inner layer is Cr2O3 layer,and some elements of Fe,Cr and Mn in the matrix diffuse into the NiO layer.By controlling the time of DC magnetron sputtering,2 h-Ni and 4 h-Ni coatings were prepared and subjected to high-temperature oxidation tests.It was found that the initial oxidation behavior of Ni samples at different sputtering times was similar.In the long-term high temperature oxidation experiment,the surface oxide film of the sputtered 2 h and 4 h-Ni samples is also a double-layer oxide structure with NiO on the outer layer and Cr2O3 on the inner layer,but compared to the sputtered 1 h-Ni sample.The resulting Cr2O3 layer is thinner,showing a stronger ability to inhibit the outward diffusion of Cr,and the content of Fe,Cr and Mn in the NiO layer is lower.After 10 weeks of oxidation,the surface specific resistance of the oxide film of the sputtered 2 h-Ni sample is the smallest,which is 89.85 mΩ·cm2,which meets the standard.