Study On The Tribology Properties Of Phenolic Resin-based Friction Materials Modified With Coupling Hybrid Nanoparticles Fillers

With the rapid development of modern automobile industry,people have higher demand for vehicle comfort,stability and safety.This requires brake friction materials own stable and proper friction and wear performance under high speed and high load conditions.The friction and wear properties of brake friction materials depend on the regulation of the friction reducing fillers,but the current widely used micron grade friction reducing fillers often need a larger amount of addition to achieve the corresponding friction reducing and wear resistance.Under high speed and high load,a large number of friction reducing fillers are easily separated from the matrix.This can cause a sharp fluctuation in tribological properties.In order to solve this problem,the nano filler is introduced as a friction reducing filler.Nano fillers have excellent properties such as small size,large specific surface area and high surface activity,which make nano filler form strong interface with friction material matrix.Thus,the tribological properties can be effectively improved when the nano filler is in low additions.At the same time,it also has good thermal and mechanical properties.In the existing study of nano fillers for friction materials,the excellent tribological properties of graphene and its derivatives have been widely recognized.However,because of the thin and soft layer of graphene and its derivatives,lamellar wrinkle and interlayer agglomeration are very serious.For that reason,graphene and its derivatives have not been directly applied to phenolic resin based friction materials only through ball milling mechanical blending.This seriously hinders the large-scale application of graphene in friction materials.Therefore,this paper proposed to suppress the wrinkle of the graphene sheet layer by spatial confinement and select the rigid two-dimensional nanoscale layer and the bar like nano metal oxide as the limiting medium.In this work,two kinds of nano fillers were synthesized and were used as the filler of the phenolic resin based friction material respectively.One of the two kinds of nanoparticles is heterogeneous coupling nanoparticle?GO-Zr?AE?₃P?.A rigid organic zirconium phosphonate?Zr?AE?₃P?layer was inserted into graphene oxide?GO?layer via layer by layer in a self-assembly manner to obtain this nanoparticle.The other nanoparticle is GO/?-Fe₂O₃ which is obtained via in-situ depositing?-Fe₂O₃ on the GO layer.Effects of the two kinds of nano-fillers on the tribological properties of the phenolic resin based friction materials were investigated.After coupling or in-situ depositing,the agglomeration of GO is obviously improved,which allows these two nanoparticles to be applied to the phenolic resin based friction material by mechanical ball milling.In this study,the Raman spectra?Raman spectra?,infrared spectroscopy?FTIR spectra?and transmission electron microscope?TEM?were used to characterize the synthesized nanoparticles.Also,the mechanical properties,thermal properties and friction and wear properties of modified composites were tested.Finally,the wear morphology of the friction material was observed by scanning electron microscope?SEM?and its wear mechanism was studied.Research indicates:?1?.Mechanical properties of the phenolic resin based friction materials have been fully improved after the modification of nano-filler?GO-Zr?AE?₃P?.The impact strength increased by 38.71%,the bending strength increased by 34.02%,and the flexural modulus increased by 17.09%,compared with the samples without nano-filler.The test results of friction and wear showed that the nano filler can reduce the wear rate greatly while maintain the basic stability of the friction coefficient.When the addition of the nano-filler was about 5 wt%,the sample showed the best tribological property and the wear rate reduced to about 20%.The properties of 5 wt%GO-Zr?AE?₃P sample were further tested when the 0 wt% GO-Zr?AE?₃P sample and 5 wt%Zr?AE?₃P sample were selected as contrastive samples.The test results showed that the friction and wear properties of 5 wt% GO-Zr?AE?₃P samples have the highest relative stability under the condition that the sliding speed and the load change constantly increase.This indicated that the heterogeneous coupling two dimensional nano filler?GO-Zr?AE?₃P?can effectively improve the tribological properties of phenolic resin based friction materials,and can be used as a solid lubricant for friction materials.In order to further study the properties of nano-filler modified friction material,the thermal gravimetric?TG?test,dynamic thermal mechanical performance test?DMA?and thermal conductivity test of the above three kinds of materials were also carried out.The experimental results showed that the nano filler can effectively enhance the thermal stability and thermal conductivity of phenolic resin based friction materials,while the enhancement of thermal stability and thermal conductivity can enhance the tribological properties of friction materials.The SEM test of the wear surface showed that the surface of the phenolic resin based friction material with nano-filler?GO-Zr?AE?₃P?was more compact and smooth.This is in agreement with the results obtained by the friction and wear test.In summary,the heterogeneous coupling nano filler GO-Zr?AE?₃P owns excellent tribological properties and the binding of zirconium organophosphate?Zr?AE?₃P?and graphene oxide?GO?can produce a synergistic effect on the tribological properties.?2?.Nano-filler GO/?-Fe₂O₃ was used to modify the phenolic resin through ball milling blending.The thermal stability of the modified phenolic resin was tested.The test results showed that when the mass fraction of GO/?-Fe₂O₃ was about 3 wt%,the thermal stability of modified phenolic resin had the most effective improvement.The initial decomposition temperature was 259?,which was 49? higher than the pure phenolic resin.The temperature of the residual rate of 90wt%was 81? higher than that of the pure phenolic resin.Use the above GO/?-Fe₂O₃ modified phenolic resin to prepare the phenolic resin based friction material,and the friction and wear test samples can be obtained by ball milling.When used the 3 wt% GO/?-Fe₂O₃ modified phenolic resin,the friction coefficient of phenolic resin based friction materials reduced by 20%and the wear rate reduced to about 30% compared with the no adding nano-filler sample.In addition,the 3 wt% GO/?-Fe₂O₃ sample can maintain a relatively stable tribological performance under the condition that the sliding frequency,load,and temperature are increasing respectively.