High-temperature Behavior Of TiN And TiN/Ni Coating On Stainless Steel

Solid oxide fuel cell(SOFC)is a novel electrochemical device that converts directly chemical energy from fossil fuel into electricity.It can solve the crisis of energy resource shortage and protect our environment.As one of the key components of SOFC,interconnect generally plays a positive role in connecting with individual cells,separating oxidation gas from fuels and supporting structure for SOFC stacks.With the decrease of SOFC working temperature to 600～800℃,ferritic stainless steel(FSS)becomes the most promising metallic interconnects candidate.However,during the long-term operation FSS interconnect suffers from volatile Cr2O3 poisoning cathode and poor oxidation resistance.Preparing protective coatings on the surface of FSS can solve the problem effectively.But there will be the mutual diffusion behavior between coatings and FSS,which reduces the oxidation resistance of coatings.Mutual diffusion area causes coating/substrate adhesion degradation.As a result,a diffusion barrier layer need to be prepared between FSS and coating.TiN,which was used as diffusion barrier layer,was prepared on the SUS430 FSS by multi-arc ion plating(MAIP),Ni coating was prepared on the surface of TiN by direct current(DC)magnetron sputtering to obtain composite coating of TiN/Ni.The oxidation performance of TiN and TiN/Ni coated steel and the electrical properties of the oxide scale were investigated.The main results are as follows:The short-term and long-term oxidation behaviors of TiN coated steel were studied at 800℃ in air.The oxide scale on the surface of coated steel after oxidation converted into bilayer structure,consisting of top TiO2 scale and protective inner Cr2O3 layer.A thin TiN coating was protected between substrate and oxide.Long-term oxidation behavior demonstrated that the TiO2 outer layer improved oxidation resistance,and reduced Cr out-migration.oxide/TiN/substrate adhesion was fine,and the area specific resistance(ASR)of oxide scale is 416.88 mΩ·cm2 after 10 weeks oxidation.The short-term and long-term oxidation behaviors of TiN/Ni coated steel were discussed at 800℃ in air.Ni was initially converted to NiO outer layer.Cr from substrate could cross the TiN layer and be oxidized to Cr2O3 inner layer.At the same time,a small amount of TiN converted to NiTiO3 at the interface of Cr2O3/NiO.TiN coating stop the mutual diffusion between Ni and steel.Long-term oxidation behavior indicated that NiTiO3/NiO layers reduced significantly Cr with high electrical performance.After 10 weeks oxidation,the ASR of oxide scale was 37.58 mΩ·cm2.