Study On Corrosion Behavior Of AlSi/BN Sealing Coating In Marine Environment

As a functional coating,seal coatings are wildly used in aircraft engine.The main constituents of seal coatings are metallic phases,nonmetallic phases and voids.When the turbine machinery used in a corrosive environment,the metal phase or the non-metallic phase may form a pair of galvanic corrosion and the occurrence of local corrosion,and it can bring hidden dangers.In this work,galvanic corrosions of the functional layers on the seal coating system were investigated by means of electrochemical noise,polarization curve,and electrochemical impedance spectroscopy(EIS).The measurement methods,which consisted of SEM,XRD and confocal techniques,were used to study the different functional layers in marine environment.The porosity of surface layer was tested by different testing methods.The results of different methods were compared and analyzed,which provided the theoretical basis for the accurate measurement of coating porosity.From the results of electrochemical noise,the following conclusions can be drawn:galvanic corrosion can occur between AlSiBN coating and NiAl coating,NiAl coating and GH4169 substrate.In the system of AlSiBN coating and NiAl coating,the AlSiBN Coating was as the anode andcorrosion of the metal phase within the coating dissolved.The galvanic corrosion current density was 29.289 ?A / cm2,which meaned thegalvanic corrosion grade was E-class.In the system of NiAl coating and the substrate of the galvanic couple,the NiAl layer was as the anode.The galvanic corrosion current density was 1.4875 ?A / cm2,which meaned the galvanic corrosion grade was the C-class.After the end of the galvanic corrosion experiment,two groups of the anode galvanic corrosion resistance decreased.Combined with microstructure analysis,it can be found that the localized corrosion,including pittingoccured in the coating surface.The results of NSS experiments showed that the corrosion of the metal phase occured in the AlSiBN coating in the salt spray environment.After the salt spray test,a large amount of gelatinous material appeared on the coating surface.After the dehydration and drying,the corrosion product became white flocculent.The results showed that the white corrosion product was Al2O3 and the yellow-green corrosion product and white corrosion product on the surface of NiAl coating appeared after the salt spray test.With XRD analysis,Yellow-green corrosion products was NiO,and white corrosion products was Al2O3.From the micrograph,it can be seen that the some corrosion products distributed inclusion and some corrosion products existed separately.The distribution of the corrosion products proved that the uneven distribution of the metal phase in each part of the coating caused the different parts of the corrosion reaction.In this work,buoyancy method and image analysis method were used to analyze the porosity of the coating layer.The porosity of the coating was 9.87% by buoyancy method.The porosity of the coating was about 12% by image analysis method.