Preparation And High Temperature Oxidation Behavior Of CrN/Ni Composite Coating On Stainless Steel

Solid oxide fuel cell is a new type of energy conversion device,which can directly convert chemical energy into electrical energy.Due to its high conversion efficiency,environmental friendliness and wide fuel sources,it has been widely studied and applied in the world.Connector is an important component in SOFC,which not only plays the role of electrical connection in the battery stack,but also plays the role of conducting airflow.Due to the excellent comprehensive performance of stainless steel connector,it has gradually become the mainstream connector material.However,the stainless steel connector will volatilize Cr in the high temperature environment for a long time,resulting in the attenuation of battery performance caused by Cr poisoning.At present,the preparation of protective coating on the surface of stainless steel connector is one of the commonly used solutions,but the element mutual diffusion between the protective coating and the stainless steel substrate will lead to the decrease of the comprehensive performance of the coating,thus losing its protection.The preparation of diffusion barrier layer between coating and substrate can well solve this problem.The main results of this paper are as follows:The short-term and long-term oxidation behavior of CrN/Ni coated stainless steel in air at 800℃ was studied.During the oxidation process,NiO is firstly formed on the surface of the coating.Because the oxygen partial pressure required for the formation of Cr2O3 is lower than that required for the formation of NiO,the Cr in the CrN layer diffuses outward and a continuous Cr2O3 layer is gradually formed beneath the NiO layer,which inhibits the further oxidation of the Ni layer.When the CrN layer is decomposed to discontinuity,the inter-diffusion between the substrate steel and Ni layer occurs,thus forming the inter-diffusion zone composed of CrN and NiCr-Fe alloy phases.Moreover,due to the selective oxidation of Cr,the internal oxidation of Cr occurs in the interdiffusion zone near the Cr2O3 layer and some holes are formed.After 10 weeks of oxidation,the ASR of the oxide film on the sample surface was 30.672 mΩ·cm2.The CrN/Cr2O3/Ni composite coating was obtained by pre-oxidation of CrN layer and sputtering deposition of Ni layer.The short-term and long-term oxidation behavior of the composite coating in 800℃ air was studied.Since a 2.1 μm Cr2O3 layer was formed between the CrN layer and the Ni layer,there was no element mutual diffusion between the CrN layer and the Ni layer in the initial oxidation process.Therefore,the internal CrN layer could stably exist,and the surface layer structure was CrN/Cr2O3/NiO.Compared with the unpreoxidized CrN/Ni composite coating,the stable CrN layer in the preoxidized coating well inhibits the element diffusion between the Ni layer and the substrate.The long-term oxidation results show that the pre-oxidation composite coating effectively inhibits the outward migration of Fe,Mn and Cr in the matrix,and exhibits good electrical conductivity.After 10 weeks of oxidation,the ASR of the oxide film on the sample surface at 800℃ was 31.937 mΩ·cm2.