Corrosion Behavior And Mechanism Of NiCrAl-based Sealing Coatings In Simulated Marine Environment

Sealing coatings improve aero-engine efficiency by controlling the rotation of aero-turbine engines and the clearance between fixed components.The metallic phase provides strength and wear resistance,while the porosity and non-metallic lubricated phase are used to ensure wearability.In addition,a layer of bonding layer,usually NiAl,is needed between the surface layer of the sealing coating and the matrix to enhance adhesion.Therefore,because of various performance requirements,usually has a complex porous seal coating,multiphase and multilayer structure to make it more susceptible to corrosion in the extreme environment,such as high humidity and high salt Marine atmospheric environment,with the increase of the number of aircraft in moored in the Marine environment,engine used seal coating coating corrosion is inevitable.In this paper,NiAl bonding layer was sprayed on GH907 substrate by plasma spraying technology,and NiCrAl-NiC and NiCrAl-BN surface layer were sprayed.Two seal coating system is studied in the simulation process of corrosion in Marine environment,with laser confocal microscope,Scanning Electron Microscope（SEM）analysis of process of corrosion morphology,using X-ray diffraction（XRD）,X-ray Photoelectron Spectroscopy（XPS）analysis on composition of corrosion products,through Electrochemical Noise（EN）,Electrochemical Impedance Spectroscopy（EIS）and potentiodynamic scanning electrochemical behavior for sample for analysis.The galvanic corrosion process of each layer coupled to each other in NaCl solution shows different corrosion behaviors.The NiCrAl-NiC coating is severely corroded as an anode due to its low open circuit potential.The NiCrAl-BN coating acts most of the time as a cathode and is less corrosive.GH907 showed obvious pitting behavior in NaCl solution,and the electrochemical noise test of each coating also showed a tendency of pitting.In salt spray environment,NiCrAl-NiC coating system is severely corroded,and the corrosion resistance decreases with corrosion time.Corrosion products accumulate on the surface of the sample,but their protection is limited,and the corrosive medium even invades the substrate.and causes corrosion.The corrosion products are mainly Ni,Al and Fe compounds.NiCrAl-BN coating system is relatively dense,and the generated Al₂O₃and Cr₂O₃ oxide films are also protective.The corrosion mainly occurs in the surface layer and fails to further corrode the substrate.In the process of hot corrosion,NiO is the main component of the oxide skin of the two coatings.The corrosion of NiCrAl-NiC coating system is relatively mild due to the coordination of C consumption of O₂ and the production of dense oxide skin NiCr₂O₄.The NiCrAl-BN coating system was severely damaged on the surface of the specimen during the hot corrosion process,resulting in loose and porous oxide skin,which was not protected from further corrosion.