Corrosion Resistance Of Alloy Coatings On Bipolar Plate Prepared By Thermal Spraying

As an important component of Proton Exchange membrane Fuel Cell（PEMFC）,metal bipolar plates play an irreplaceable role,but the weak acidic working environment makes bipolar plates vulnerable to corrosion.As a mature surface modification technology,thermal spraying has the advantages of simple operation and low cost.It can greatly reduce production cost and improve the efficiency and economic value when applied to the modification of bipolar plate.In this study,atmospheric plasma spraying（APS）and high-velocity oxygen-fuel（HVOF）were used to prepare metal alloy coatings,and the effects of spraying process,hole sealing treatment and vacuum heat treatment on the corrosion resistance of the coatings were studied.Firstly,Ni,Ni Cr BSi,Ni Cr Al Y and Fe Al coatings were sprayed by atmospheric plasma spraying,and the best corrosion resistance of the four materials was selected as the subsequent test material.Secondly,the influence of process parameters and hole sealing treatment on the corrosion resistance of Ni Cr Al Y coatings sprayed by APS were studied.Finally,the influence of vacuum heat treatment and hole sealing treatment on the corrosion resistance of Ni Cr Al Y coatings sprayed by HVOF were studied.The microstructure and phase structure of the coating were characterized by scanning electron microscope（SEM）,optical microscope and X-ray diffractometer（XRD）,and the corrosion resistance was studied by electrochemical workstation.According to the experiment,the following conclusions are obtained:（1）Study the corrosion resistance of different materials.The results show that Ni Cr Al Y coating has the best corrosion resistance.Mainly because Ni Cr Al Y powder into regular spherical,the formation of the least porosity,reduce the corrosion solution into the coating,and then corrosion matrix.All four metal materials are completely corroded during the corrosion process,so spraying technology alone cannot fully protect the matrix.（2）The influence 200 A,300 A,400 A and 500 A current intensity on the corrosion resistance of Ni Cr Al Y coating prepared by APS was studied.The results show that when the current intensity reaches 400 A,the corrosion current density is the lowest and the corrosion resistance is good,mainly because with the increase of current intensity,the particle melting effect is enhanced and the existence of pores is reduced.The increase of Ni Cr relative content can improve the corrosion resistance of the coating.When the current intensity is 500 A,the excessive multilayer gap caused by particle flattening will decrease the corrosion resistance of the coating.（3）The influence of vacuum heat treatment at 800℃,1000℃and 1200℃on the corrosion resistance of Ni Cr Al Y coating prepared by HVOF was studied.The results show that the Ni Cr Al Y coating has the best corrosion resistance after 1200℃,mainly because with the increase of the temperature of vacuum heat treatment,the coating density is improved,and the influence of structural defects and component segregation is reduced.The microstructure ofβ-Ni Al phase is coarser,and the newγ’-Ni₃Al phase appears with finer microstructure and increased number,which provides favorable conditions for diffusion of Al element and formation of passivation film.（4）In view of the structural defects of HVOF and APS,the influence of pore sealing agent of epoxy resin on the corrosion resistance of Ni Cr Al Y coating was studied.The results show that the addition of pore-sealing agent prevents the corrosion solution from entering the coating,and then blocks the corrosion matrix.But when there are too many structural defects,the effect of sealing agent is not obvious.