Fundamental Research On The Chemically Bonded Ceramic Coatings Reinforced By Graphene

With the development of science and technology, the requirements for surface protections of mechanical assemblies is becoming stricter because of the terrible working conditions. To meet these requirements, it is necessary to improve the corrosion resistance, wear resistance and bond strength and reduce the friction coefficient of the chemically bonded ceramic coatings. The related investigations were conducted in the present paper.Firstly, the curing analysis was conducted by thermodynamics. The dissolutions models of metal oxide with pH and temperature were developed, which could guide the curing process of the chemically bonded ceramic coatings. Besides, the curing mechanism of the coatings was also clarified with the analysis of SEM, Raman and DSC. The graphene had no effect on the curing of the coatings.The corrosion behaviors of the coatings with nano-alumina and graphene were studied, respectively. With the introduction of nano-alumina and graphene, the corrosion resistances of the coatings both increased, and the improvements were increased with the increase in the content of nano-alumina and graphene. However, it was also found that, the influence of graphene in improving the corrosion resistance of the coating was better than that of nanoalumina. In addition, the improving mechanism in corrosion resistance of nano-alumina and graphene were also investigated, respectively. It is found that, particles were attracted around the nano-particles because of the surface effect of the nano-particles. This strong combination could prevent the appearance of cracks. Besides that, the formed cracks could hardly breakdown the strong combination, and the crack must change the pathway. These made the access of O2, H2 O and Cl- to the substrate more difficult, and the corrosion resistance was improved. The ceramic platelets could be found in ceramic coatings when adding the graphene. These formed ceramic platelets and the graphene platelets blocked and changed the diffusion pathways of O2, H2 O and Cl- which made the pathway more tortuous. Besides, the graphene platelets bridged the crack and prevented the crack becoming wide. This also resulted in the higher corrosion resistance.The friction behaviors of the coatings with graphene were investigated on a wear testing machine using a ball-on-disc configuration in linear reciprocating mode. It was found that, the friction coefficient of the coating decreased with the increase in graphene. The wear volume showed the similar trend. With the analysis of SEM, the wear surface of the coating with graphene possessed a smooth surface with a little of debris and cracks. This smooth surface could decrease the friction coefficient between GCBPCs and the counterpart ball. Besides that, the graphene lubricant film was found on the surface. This also contributed to the lower friction coefficient. The decrease in the wear volume was mainly because the platelet graphene could improve the mechanical property of the ceramic, which made the ceramic more tolerant to damage during the wear volume. The graphene lubricant film also contributed to the lower wear volume.A novel elastic-plastic contact model considering the effect of frictional tangential stress was presented. The present model was developed based on the assumption that the transitions from elastic, through elastic-plastic, to fully plastic deformation of a contacting asperity was continuous and smooth. Based on this model, a mathematical model for the influence of the anti-friction material on friction was presented. In this mathematical model, the amount of antifriction material that was squeezed out also continuously increased in elastic-plastic deformation stage, which solved the expression of the lubricant film area. To clarify the prediction of the model, the predictions were compared with the experimental results. It was found that the predictions had the similar trends with the experimental results. The predicted results showed that the friction coefficients decreased with the increase in graphene. And the friction coefficients decreased with the increase in the normal force at first and achieved plateau. This mathematical model presented a friction prediction of coatings with anti-friction material and provided the theoretical guidance for coating designing.At last, the bond strength between the coating and substrate was investigated with finite element method. The simulated results showed that, with the introduction of interlayer, the bond strength between the coating and substrate could be obviously improved. Besides, effects of elastic modulus, thickness of the interlayer and thickness of the coating on the bond strength for coating-substrate system were also investigated. This simulations provided the theoretical guidance for coating designing and interlayer selection.