| The thermal spraying Al2O3 coating has many advantages such as high hardness,wear resistance,corrosion resistance,high temperature resistance and chemical stability,which provides an important guarantee for the application of flight deck in marine environment.However,the structural defects（pores and cracks）have become the main reasons that affect the long life and reliable service of thermal spraying coatings.The current research methods mainly reduce the porosity of coating by sealant.That is to use soaking,coating and other ways to infiltrate the sealant into the coating to improve the structural defects.But there will be the following two problems:one is limited by the viscosity of liquid sealant,cannot penetrate the tiny pores and cracks;Second,due to the volume shrinkage and gas escape during the curing process of the hole sealant,there are structural defects,and the barrier ability of the corrosive medium is insufficient.Therefore,it cannot effectively solve the structural defects of thermal spraying coating in extreme corrosive environment.In order to further seal coating pores,block corrosion channels and maximize coating service life.In this paper,a high density and high reliability thermal spraying Al2O3 ceramic coating was prepared by supersonic plasma spraying and sealant infiltration alternating deposition technology.Focusing on the two key points of the deposition of molten Al2O3 particles and the sealing of the pore on the Al2O3 thin layer in the process of alternating deposition,the phase composition and microscopic morphology of the coating were analyzed by XRD,SEM,EDS and micro-CT,and the forming mechanism of the alternately deposited coating was further studied.Orthogonal experiment was used to optimize the process parameters of thermal spraying and single factor experiment was used to investigate the influence of the process parameters of alternately deposited coating.The effects of the alternately deposited technology and the traditional sealed method on the mechanical properties,corrosion resistance and wear resistance of the coating were compared and analyzed by microhardness tester,universal testing machine,full immersion corrosion,electrochemical corrosion and friction and wear testing machine,which provided a theoretical basis for the preparation of high-density thermal spraying coating.The main conclusions of this paper are as follows:（1）Alternately deposited coating technology can further close the internal defects of the coating and improve the compactness of the coating.Exploration experiments showed that the porosity of the alternately deposited coatings decreased to 1.34%compared with the sprayed Al2O3 coatings and the traditional sealed Al2O3 coatings（4.69%and 3.05%）.It is still necessary to explore the spraying process parameters and sealing parameters of alternately deposited coating.（2）The forming mechanism of alternately deposited coating was revealed.The high density of the alternately deposited coating mainly depends on the sealant can effectively penetrate and close the pores of the thermal spraying Al2O3 thin layer,and then the solvent deposited by the molten Al2O3 particles quickly volatilizes and transforms into the gel state of the sealant surface,and the sealant binds the Al2O3 particles to the surface in the form of an adhesive.For the alternately deposited coating,the sealant can effectively seal the pores of the coating,and a large number of sealant sheets are randomly and cross-distributed in the coating,which greatly improves the barrier ability of the coating to the corrosive medium.（3）The spraying process parameters of Al2O3 were optimized by orthogonal experiment with two-dimensional porosity of coating as index.The optimal spraying process parameters are:spraying voltage>Ar air flow rate>spraying distance>spraying current,Optimized spraying process:spraying voltage 140 V,Ar gas flow rate 100 L/min,spraying distance 120 mm,spraying current 440 A.The two-dimensional porosity of Al2O3 coating prepared by optimal spraying process parameters was 2.4%.The influence of sealing process parameters of alternately deposited coatings on the corrosion current density was discussed by single-factor method,when surface temperature of the coating is 70±5°C as the sealant is brushed,the impregnate time of the sealant is 10±1 min,the plasma flame flow is preheated three times,and the thickness of the layer of single sealed thin coating is 20μm,the prepared alternate deposition coating has the best performance,the icoor of coating is the lowest,1.04×10-7 A/cm2.（4）The optimal spraying process parameters and sealing process parameters were used to prepare alternately deposited coating.The mechanical properties of the coating are improved.,the average microhardness of the alternately deposited coating is 1140 HV0.1,and the cohesive bonding strength between the coating is about 25.496 MPa.The corrosion resistance of the coating has been significantly improved,the icoor of alternately deposited coating is 1.04×10-7A/cm2,80%lower than traditional sealed coatings;the Ecoor of alternately deposited coating is-350 m V,74 m V higher than traditional sealed coating.For the 120μm thick alternately deposited coating,the impedance modulus of the alternately deposited coating at different soaking times was higher than that of the traditional sealed coating,and Rp of the alternately deposited coating after 20 d immersion is 5815Ω·cm2,which is about 3.2 times that of the traditional sealed coating.For wear performance,the wear rate of the alternately deposited coating is 1.06×10-5 mm3/N·m,which is basically the same as that of the traditional sealed coatings,only 4%of the Al2O3 coating. |
