| With the continuous upgradation of advanced equipments,Cu-based friction materials(CBFMs)are suffering extreme working conditions such as high speed,heavy load and high temperature.As the paramount part of braking and gearing rigging,CBFMs are of great importance to the safe,reliable and stable operation of those equipments.However,the problems like friction coefficient(COF)heat fade,excessive abrasion and low strength have become the bottleneck problems restricting the further development of advanced equipments,and they are also the popular topic in tribology field.Therefore,it is super-important to develop high-peformance CBFMs and they are useful to enhance the service life of advanced equipments,promote China to seize the commanding height in future study and accelerate the future tribology theory development.Based on the above problems and requirements,this study optimized physical,mechanical and tribological properties of CBFMs from the perspectives of structure design and process optimization according to Bionic Theory and Finite Element Method;the regulatory mechanism of tribological properties by wet granulation was mainly explored;the mechanisms of enhanced comprehensive performances by 3D mesh structure was elucidated and the influences of enhanced tribological behaviors by bionic texture was revealed,and thus provided theoretical and practical basis for performance improvements of CBFMs.The main researches and innovation achievements are as follows:(1)Raw materials gathering in Cu and C systemwas a technical bottleneck which would decrease the comprehensive properties.To solve this problem,a new processing method was proposed by wet granulation for the fabrication of CBFMs.During wet granulation process,Acrylic Resin with low molecular weight was used as binder and Anaqueous Ethanol was used as bridging liquid.Wet granulation can decrease the fluidity of raw materials powders to prevent the refractory raw materials gathering,thus improve the comprehensive properties.In addition,wet granulation can also construct a soft/hard alternating periodic structure inside CBFMs,hard regions can be used as the nucleation sites of wear debris,promoting the formation of secondary plateaus and enhancing its tribological performances.In this study,CBFMs were prepared by prefabricated particles with different diameters,and physical,mechanilcal and tribological properties were investigated.To analysis wear mechanisms,worn surface morphology and components were characterized by SEM and EDS and finally the comprehensive properties of CBFMs were optimized.(2)Based on the past deficiency of appreciating composition optimization and neglecting structure design of CBFMs,3D mesh structure was constructed inside CBFMs by processes of step mixing,wet granulation and particle coating.3D mesh structure inside CBFMs could greatly improve the comprehensive properties because of its high strength,which was due to the stronger sintering character by smaller size of tiny Cu powders.Furthermore,3D mesh structure constructed by tiny Cu powders has no complex interfaces,which has a stronger heat conduction and can quickly conduct a lot of heat out of CBFMs when braking,preventing COF heat fade and improving its wear resistance.Among them,physical,mechanical properties and wear resistance of CBFMs with 3D mesh structure have been greatly improved,its COF stability was the highest at each braking speeds and was suitable for more complex braking conditions.(3)In order to optimize tribological behaviors of CBFMs with 3D mesh structure,a new method was proposed based on wet granulation and particle coating.Size of 3D mesh structure was controlled by the prefabricated particles diameter based on wet granulation,thickness of 3D mesh structure was controlled by the quality of tiny Cu powders on the prefabricated particles surface based on particle coating,thus adjusting the comprehensive properties.Through physical,mechanical and tribological properties test and wear mechanism analysis,the friction stability and wear resistance mechanism of 3D mesh structure were revealed.Among them,the samples prepared with prefabricated particles of 3～5 mm and tiny Cu powders of 25 ωt% had the best comprehensive properties,its compressive and wear resistance have been greatly improved.(4)On the basis of above researches,by optimizing sintering process,CBFMs with 3D mesh structure was synergisticly strengthened by structure design and process majorization,thus improving its comprehensive properties.The influences of different sintering temperature and sintering time on physical,mechanical and tribological properties were explored,the friction stability and wear resistance mechanism at different sintering processes were expounded.With increasing sintering temperature,wear rate of samples showed a decreasing trend;with the extension of sintering time,wear rate of samples also showed a gradually decreasing trend,and the influence of sintering temperature on wear rate was higher than that of sintering time.Sample sintered at 950 ℃ and 120 min had the best comprehensive performance,compressive strength was the most optimal and wear rate was the minimum.(5)On the basis of above structure design,bionic non-smooth surface on CBFMs was constructed according to bionic tribology principles to solve the problem of abnormal abrasion causing from excessive stress during friction.Stress distribution of different bionic texture were explored,the most optimal bionic texture was slected which was pits on Dung Beetle coupled with hexagon on Eryx tataricus,and the bionic texture parameters were optimized by Response Surface Methods.Among them,bionic texture could regulate stress distribution,reduce stress concentration and circularly recycle wear debris during friction,which could reduce abrasion.Compared with smooth friction surface,wear rate of bionic non-smooth surface was reduced by 19.31%. |
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