Investigation Of The Wear Resistance And Anti-corrosion Of The Ceramic Coatings Reinforced By Hybrid Carbon Materials And Its Working Mechanism

The chemically bonded ceramic coatings are widely used in the surface protection of large machines and components because of their low curing temperature,easy on-site usage,and low cost.However,the weak bonding strength between the reinforcements,such as graphene oxide,and other phases in the coating,the high corrosive and wear impose challenges on the service life of the chemically bonded ceramic coatings.In this paper,the graphene oxide and carbon nanotubes were modified with the metal oxides to improve the bonding strength between carbon materials with ceramic matrix.In addition,the influences of modified graphene oxide and carbon nanotubes on the corrosion resistance and tribological properties of ceramic coatings were investigated.These studies provide important experimental and theoretical basis for ceramic coatings with carbon nanomaterials.（1）Nano-alumina decorated graphene oxide（GO-Al₂O₃）were prepared and characterized by XRD,FT-IR,TGA,SEM and TEM.It was found that the distance between GO layers increased after decoration,but the main structure was not destroyed,and alumina particles were distributed on the surface of GO.Zinc oxide decorated multi-wall carbon nanotubes（MWCNTs-ZnO）were synthesized by sol method.The bonding interface between ZnO and MWCNTs could be clearly seen through TEM,and ZnO were distributed on the surface of MWCNTs without serious clustering.（2）GO-Al₂O₃ and MWCNTs-ZnO were added into the ceramic coatings as functional reinforcements,separately.It was found that there was no new characteristic peaks appeared in the coating structure,indicating that the hybrid carbon material did not participate in the curing reaction of the coatings.Through the reaction between the metal oxide and the binder,the hybrid carbon material and the ceramic matrix were combined to form a denser coating structure,so that the ceramic coatings showed higher hardness and lower roughness.（3）Electrochemical experiments were used to study the corrosion resistance of ceramic coatings with GO-Al₂O₃.It was found that,the corrosion resistance of ceramic coatings were improved by the addition of GO-Al₂O₃.With the increase of the content of GO-Al₂O₃,the corrosion resistance efficiency of the coatings has also been improved.It was found that the addition of GO-Al₂O₃ could make the ceramic coatings denser and reduce defects such as cracks and holes.By observing the cross-sectional structure of the coatings after corrosion,it was found that GO-Al₂O₃ showed a flaky structure,which could be regarded as a physical barrier in the propagation path of cracks.The cracks cannot penetrate GO-Al₂O₃ and forced to stop or change direction,consuming a certain amount of fracture energy.Besides that,the cracks could breakdown the weak bonding between GO-Al₂O₃ and the ceramic matrix,which consumed more fracture energy,and the cracks were further blocked or changed the diffusion pathways.（4）The results of electrochemical experiments showed that the corrosion resistance of the ceramic coatings was improved with the increase of MWCNTs-ZnO.When the corrosion medium（H₂O,O₂,Cl^-,etc.）diffused inside of the ceramic coatings,the cracks cannot penetrate MWCNTs-ZnO and the direction was forced to change.The strong combination between MWCNTs-ZnO and the ceramic matrix could consume more fracture energy when cracks propagate along MWCNTs-ZnO.The diffusion path becomes more tortuous and longer,which makes it more difficult for the corrosive medium to the substrate.In addition,MWCNTs-ZnO bridged the cracks,further suppressing the propagation of cracks.（5）The addition of GO-Al₂O₃ could effectively reduce the friction coefficient and wear rate of ceramic coatings on a wear testing machine in linear reciprocating mode.It was found that the carbon content on the wear surface was significantly increased compared to the non-wear surface,and a carbon material lubrication film was formed on the wear surface.The wear surface of the grinding ball became smooth by addition of GO-Al₂O₃,and there was no obvious groove phenomenon.Besides,the smooth wear surface could reduce the rough peak pressure on the wear surface,thereby reducing the wear rate of the coatings.In addition,the bonding strength of the ceramic matrix was improved by the addition of GO-Al₂O₃,and the particles were difficult to pull out from the ceramic matrix.（6）The addition of MWCNTs-Zn O could effectively reduce the friction coefficient and wear rate of ceramic coatings.It was found that the wear area and the volume of the grinding ball was reduced by the addition of MWCNTs-ZnO in the ceramic coatings.In addition,MWCNTs-ZnO could reduce the coating surface roughness,and MWCNTs-ZnO were squeezed out and adsorbed on the wear surface to form smooth wear surface,which could reduce the shear strength between the coatings and the grinding ball.Thereby reduced the wear rate of the ceramic coatings.Besides,the bonding strength between ceramic matrix were improved by the bridging effects of MWCNTs-ZnO,which could reduce the ceramic matrix peeling off during the friction process,thereby reducing the wear rate of the ceramic coatings.（7）The introduction of an interlayer in the coating system could significantly reduce the Mises stress.With the increase of the elastic modulus of the interlayer,the Mises stress abruption at the coating/interlayer interface decreased and increased at the interlayer/substrate interface.Under the same load,the effective elastic modulus and hardness of the coating system increased with the increase of the yield strength of the interlayer.Moreover,the effective elastic modulus and hardness of the coating system decreased as the maximum load increased.However,there was no Mises stress abruption inside of the gradient coatings,and the Mises stress abruption at the coating/substrate interface was small.Increasing the elastic modulus gradient value could effectively reduce the plastic strain of the coatings and reduce the Mises stress abruption at the coating/substrate interface.However,a large value caused a large plastic strain of the substrate.When the load was small,the yield strength gradient value has no effect on the stress of the coating system.When the load was large,the plastic deformation of the coating system increased with the increase of the yield strength gradient value.