Microstructure And Salt Spray Corrosion Property Of NiCrAlY Coating On M50 Steel By Elecrospark Deposition

NiCrAIY coating has been widely used in the field of anti corrosion coating because of its excellent corrosion resistance and oxidation resistance.There are many methods to prepare NiCrAlY,the electric spark deposition(ESD)is widely used because of its low requirement to the shape of the substrate.Therefore,this research mainly focused on the microstructure and corrosion resistance properties of NiCrAlY coating fabricated by the ESD method.NiCrAlY coating was deposited on the surface of M50 steel by different deposition methods,different deposition thickness and different deposition parameters.Through the analysis of the microstructure,phase composition,bonding strength and corrosion resistance of salt spray,the parameters of electric spark deposition were obtained.Results showed that the NiCrAlY coating is uniform and compact,surface morphology of NiCrAlY was splash.Dense NiCrAlY coating deposition by rotating welding torch is dense but crack,NiCrAlY coating deposition by ultrasonic welding torch is crack free.With the increase of coating thickness,the surface roughness of the coating becomes larger,and the crack appears.The influence of deposition voltage on the coating morphology and roughness is great with the increase of the deposition voltage,the coating rooughness becomes larger and the crack appears;the effect of deposition capacitance on the morphology is small.NiCrAlY coating is mainly composed of a γ/γ’-Ni/Ni3Al phase and m-β phase.NiCrAlY coating and the substrate is metallurgical bonding,the bonding strength is high.The anti salt spray corrosion performance of NiCrAlY coating deposited by ultrasonic welding torch is superior to the rotating torch.With the increase of coating thickness,the salt spray corrosion resistance of NiCrAlY coating increased.According to the actual application conditions of the bearing,the best thickness is about 40～50 μm.The change of deposition parameters also affect the anti corrosion performance of NiCrAlY coatings,with the increase of deposition voltage and deposition capacitance,the corrosion resistance of coatings decreased,NiCrAlY coating deposition by 100 V-40 μF is best to resist salt spray corrosion.According to the comprehensive consideration of the morphology and deposition rate,salt fog performance,the best process parameters of NiCrAlY coating is ultrasonic welding deposition torch,deposition voltage 100 V.deposition capacitor 40 μF,coating thickness 50 μm.The NiCrAlY coating was prepared by the above optimal parameters and tested by the neutral salt spray test according to the national standard.The corrosion mechanism of M50 steel and NiCrAlY coating was studied.The M50 steel in salt spray products Fe2O3,during the salt spray test,Fe2O3 content increased,crack and spalling appeared on the corrosion product surface,corrosion accelerated.Eventually,a large number of corrosion pits and corrosion spalling area are formed on the surface of M50 steel.The main components of the NiCrAlY coating corrosion products formed in the salt spray environment are Fe,O,Cl,and Cr.The chemical formula of corrosion products is MexOyClz.The A1 and Fe which located in surface of the coating respectively to form Al2O3 and Fe2O3 in the salt spray process.Eventually formed a structure of four layers,from the inside to the outside are respectively M50 steel,NiCrAlY coating,Al2O3 oxide film,Fe2O3.This structure can effectively improve the corrosion resistance of M50 steel.