Study On Preparation And Tribological Properties Of PTFE Inorganic Composite Coating

As the main material for preparing hydrophobic coatings,polytetrafluoroethylene(PTFE)has excellent self-lubricating properties and a very low coefficient of friction.However,PTFE has defects such as poor adhesion,low temperature resistance and low wear resistance.As an inorganic binder,aluminum dihydrogen phosphate(AP)is pollution-free and has excellent high temperature resistance.In this thesis,PTFE,AP,alumina(Al₂O₃)and modified carbon fiber(MCF)is used as aggregate,binder,primer filler,topcoat filler,respectively,and a certain amount of film-forming additives is added to prepare excellent performance PTFE inorganic composite coating.The main research contents of this paper include:the effect of AP on the curing mechanism and tribological properties of the coating,the effect of MCF content on the tribological properties of coatings,and the effect of MCF on the tribological properties of the coating at different service temperatures.Firstly,the curing mechanism of AP inorganic binder in the coating primer and topcoat was clarified,and the influence of AP content on the tribological properties of the coating was discussed.The research of the molecular structure,phase composition and cross-sectional morphology of the coating primer by FT-IR,XRD and SEM shows that AP in the primer will react with Al₂O₃ during heating to form aluminum phosphate with high bonding effect(Al PO₄)the binding phase,which allows the coating components to bond with the substrate.SEM results show that the topcoat AP can autopolymerization at high temperature to form a binder with a macromolecular structure,result in the melted filamentous PTFE is tightly bonded to it.PTFE inorganic composite coatings with different AP content of primer and topcoat were prepared by using PTFE as aggregate and AP as binder.The results of coating performance analysis show that the adhesion of the coating increases first and then decreases with the increase of AP content of the primer,but the hydrophobic performance decreases with the increase of AP of the topcoat.When the topcoat AP content is 30 wt.%,a large amount of PTFE rises to the outer surface of the coating,and the coating surface is the smoothest.The friction and wear test results show that with the increase of AP content,the friction coefficient of the coating first decreases and then increases,while the wear resistance increases.When the AP content is 30 wt.%,the wear debris adhering to the surface of the wear scar greatly reduces the friction between the coating and the grinding ball,and significantly improves the tribological performance.Secondly,the evolution of the microstructure of carbon fiber(CF)before and after modification with bis-[?-(triethoxysilyl)propyl]tetrasulfide(Si69 silane coupling agent)were analyzed,and the effect of MCF content on the the influence of coating tribological properties were discussed.Through SEM,FT-IR and EDS,it is found that the hydroxyl group on the Si69silane coupling agent can undergo condensation reaction with the carboxyl group on the surface of CF,and it is successfully grafted to the surface of CF,and a film is formed on the surface of CF to improve the bond strength between CF and PTFE.The MCF-reinforced PTFE inorganic composite coating were prepared by filling the topcoat with different MCF content.Through the analysis of the thermal performance of the coating,it is found that MCF has little effect on the curing conditions of the coating.By studying the surface properties of the coating,it is found that when the content of filled MCF is 4 wt.%,the surface of the coating is very dense and flat;as the content of MCF increases,the hydrophobic performance decreases,but the hardness of the coating significantly increases.Tribological tests show that the wear resistance of the coating increases significantly with the increase of MCF,and the friction coefficient also increases,but the increasement is small.The results of studying the wear mechanism of the coating show that the filling of 4 wt.%MCF can make the PTFE inorganic composite coating material tightly bond and share the load with the coating.The wear scar surface of the coating is uniform and compact,and the tribological performance is the best.Finally,the influence of MCF on the tribological properties of the coating under different service temperatures was studied.The research results show that the hydrophobicity and hardness of the coating decrease with the increase of temperature;filling with MCF has little effect on the hydrophobic properties of the coating,but it can significantly increase the hardness of the coating.The friction and wear test show that the friction coefficient of the coating gradually decreases with the increase of temperature,and the wear quality and wear rate of the coating increase accordingly.At the high temperature friction of 250?,the friction coefficient,wear quality and wear rate of the unfilled MCF coating increased sharply during the friction process,while this situation do not exist in the coating filled with 4 wt.%MCF.Combined with the microstructure of the coating,it can be seen that the coating without MCF is softened during the medium and high temperature friction process,the depth of the wear scar increase significantly,and a large amount of coating material peel off from the substrate;filled with 4wt.%MCF,MCF can significantly improve the toughness of the coating,and share the load with the coating,the coating has no obvious damage,and the wear scar morphology has been significantly improved.