Performance And Mechanism Study Of Chemically Bonded Ceramic Coatings Reinforced By CNT

Modern industrial applications,such as aerospace,machinery manufacturing and energy development,put forward more and more requirements for the wear resistance,high temperature resistance and corrosion resistance of parts.For example,the friction pairs of crankshaft and bearing,valve and valve seat in high-performance engine need to do high-frequency reciprocating or rotating movement under the exhaust temperature of about 700?and the high acid exhaust gas envionment,high temperature corrosion wear is still an urgent problem to be solved.As a kind of coating,ceramic ceramic coating is being studied and applied by more and more people because of its superior characteristics.However,to promote the application in a wider range,the ceramic coating still needs to be improved in the aspects of wear and friction reduction,corrosion resistance and anti-cracking.In this paper,based on the above-mentioned aspects,further research is carried out to provide better theoretical basis and technical guidance for the application and promotion of ceramic coating.In this paper,the preparation of ceramic coating samples was studied.In order to solve the problem of poor dispersion of additives in the preparation of the coating,the carboxyl functional group was introduced into carbon nanotubes by strong acid treatment,and then the surface of carbon nanotubes was modified by surfactant.The results showed that the dispersion of carbon nanotubes in the ceramic coating increased significantly.XRD,Raman,EDS and other analysis results show that the main carbon tube structure of carbon nanotubes has not been damaged in the process of pickling and centrifugation,and in the subsequent mixing and curing process of coating slurry,carbon nanotubes do not react with other components to generate new substances.After solving the problem of coating preparation,based on the samples with good performance of ceramic coating,the friction and wear properties of samples under different curning time and CNT weight ratio were studied at room temperature.The results showed that the hardness and roughness increased first and then decreased with the increase of carbon nanotube.The mechanical properties of ceramic coating with different curing time are not obvious.The results show that the friction coefficient tends to be stable after a sharp decrease in the first 80 seconds.With the increase of the composition ratio of CNTs,the friction coefficient decreases first and then increases,and there is no obvious change trend in the friction coefficient of composite ceramic coating with different curing time.With the increase of the proportion of carbon nanotubes,the wear rate decreases first and then increases,which is directly affected by the friction surface condition.In the test sample,when the content of carbon nanotubes is 0.25 wt%,the composite coating has the best wear resistance capability.Furthermore,in this paper,the micro mechanism of the coating was analyzed by SEM.The results show that the CNT plays a good bridging role in the process of coating cracking,changes the direction of crack growth,reduces the fracture energy,and prevents further crack growth.Excessive addition of carbon nanotubes will lead to serious agglomeration in the ceramic coating,which will lead to the degradation of the anti-wear and anti friction properties of the coating.Through the rotary friction and wear experiments,the friction and wear properties of the samples with four different composition ratios of carbon nanotubes?0%,0.25%,0.75%and 1%?were studied at three temperatures?100?,300?and 500??.The experimental results show that when the temperature is lower than 500?,the number of friction systems decreases with the increase of carbon nanotubes.However,when the temperature rises to 500?,there is no obvious relationship between the friction coefficient and the content of carbon nanotubes.At500?,the friction coefficient of the coating is the same as that of the coating without carbon nanotubes.In addition,the friction coefficient of the coating with the same content of carbon nanotubes is the highest at 500?.The friction coefficient of the coating is the lowest at 300?,not 100?.The higher temperature?300??is beneficial to the formation of lubricating film on the wear track of CNT,thus reducing the friction coefficient.When the temperature rises to500?,the carbon nanotubes lose their main structure due to oxidation,and cannot form lubricating film.Therefore,at 500?,the friction coefficient is the same as that of the coating without carbon nanotubes.With the introduction of carbon nanotubes,the wear rate decreased obviously.In addition,the wear rate increases with the increase of temperature.The increase of wear rate between 300?and 100?is very small.The wear rate increases obviously between300?and 500?.The wear rate of the coating containing carbon nanotubes reached the level of the coating without carbon nanotubes at 500?.The results show that the ceramic coating at100?and 300?keeps its inherent mechanism well,and the carbon nanotubes can play a good role in lubrication and bridging.When the temperature reaches 500?,the carbon nanotubes are decomposed by heat and no longer effective.The structure of ceramic coating is affected by high temperature,its anti-wear and anti-friction properties decrease.Considering the continuity of elastic deformation,elastic-plastic deformation and plastic deformation,combined with the contact theory of asperities,the contact model of CNT reinforced chemically bonded phosphate ceramic coatings is established.On this basis,the positive pressure and friction coefficient between two rough surfaces are derived.Considering the change of coating characteristics in different temperature environments and applications,a model of CNT reinforced ceramic coating friction coefficient with temperature was proposed and established creatively.The simulation results of the model through MATLAB show the consistency with the experimental results.The electrochemistry experiment of the modified CNT reinforced chemically bonded phosphate ceramic coatings was carried out.The experimental results show that the corrosion current density(I_corr)of coated steel is significantly lower than that of bare steel,which shows that the corrosion resistance of coated steel is improved.With the increase of the content of carbon nanotubes,the corrosion resistance of the coating is also improved.The microstructure analysis results show that because of the strong strength of multi walled carbon nanotubes,the strength of the gel can be improved,the cracks can be prevented and bridging effect occurs when cracks occur,it is more difficult for corrosive electrolyte to enter the substrate surface through cracks in the coating.Meanwhile,carbon nanotubes change the diffusion path of the corrosion medium and extend the time of the corrosion medium to the substrate surface.Therefore,after the introduction of carbon nanotubes,the above-mentioned corrosion resistance has been improved.