Study On Principal Component Modified Graphite/copper Composites And Its Tribological Properties

With the rapid development of transportation,power system and electronic industry,people put forward higher and higher requirements for electrical contact materials to meet the harsh service environment such as high current and high speed,which requires electrical contact materials to have more excellent electrical,mechanical and friction and wear properties.Graphite/copper composites have excellent thermal conductivity and self-lubrication properties,and are widely used in sliding electrical contact materials.With the rapid development of transportation,power system and electronics industry,electrical contact materials are required to have more excellent electrical,mechanical and friction and wear properties to meet the high current and high speed service environment.However,graphite and copper have poor wettability and low bonding strength,resulting in many internal structural defects,which affect the electrical,mechanical,friction and wear properties of composites.Therefore,the modified materials copper foam,copper-plated expanded graphite and copper-plated carbon fiber were self-made in this study.Graphite/copper,copper-coated graphite/copper,foam copper-graphite/copper,expanded graphite-graphite/copper,copper-coated expanded graphite-graphite/copper and copper-coated carbon fiber-copper-coated expanded graphite/copper composites were prepared by powder metallurgy method.The electrical properties,hardness,bending strength and friction and wear properties of the composites were characterized,and the friction and wear mechanism was analyzed.The main research contents and conclusions are as follows:（1）The influence law of the contents of copper-coated graphite on the properties of graphite/copper composites was systematically studied.The results show that the copper plating on the surface of graphite improves the bonding between graphite and copper,which is helpful to form a more complete copper network structure and reduces the resistivity of the composites.As the content of copper-coated graphite increases from 10 wt%to 50 wt%,the density of the composite increases from 2.83 g/cm³to 2.95 g/cm³,the resistivity decreases from 0.522μΩ·m to 0.205μΩ·m,and the mechanical properties decrease.With the increase of the content of copper-coated graphite,the friction coefficient of the composites decreases,and the wear decreases first and then increases.When the amount of copper-coated graphite is 20 wt%,the friction and wear properties of copper-coated graphite-graphite/copper composite are the best,and the friction coefficient and wear rate are 0.192and 36.6×10^-6mm³·m^-1·N^-1,respectively.The experimental results of sliding friction and wear that with the current increasing from 1A to 5A,the 20 wt%copper-coated graphite-graphite/copper composite has lower friction coefficient and wear rate than the graphite/copper composites.The friction coefficient decreases by 0.006～0.027,and the wear rate decreases by 45%～50%.Copper coating provides a large number of conductive spots,resulting in less current density across the surface,generating less heat,lowering the contact surface temperature and reducing friction surface defects.（2）The properties of foam copper-graphite/copper composites with different graphite content（from 20 wt%to 60 wt%）were investigated.It is found that the copper foam-graphite/copper composites with the same graphite content have lower resistivity,friction coefficient and wear rate than the graphite/copper composites.When the graphite content is 60wt%,the resistivity,friction coefficient and wear rate of the foam copper-graphite/copper composite are 88%lower,20%lower and 22%lower than those of the graphite/copper composite.This is because the network structure of foam copper can provide conductive and thermal channels,dissipate the heat timely,protect the material structure in the process of friction,and inhibit the initiation and expansion of cracks.（3）The effect of the contents of copper-coated expanded graphite on the properties of graphite/copper composite was studied.The results show that the copper-coated expanded graphite-graphite/copper composite has lower friction coefficient and wear rate than the expanded graphite-graphite/copper composite.When the amount of copper-coated expanded graphite is 2wt%,the wear rate of the composite is the lowest,which is 1.2×10^-3mm³·m^-1·N^-1.（4）The influence law of copper-coated carbon fiber on the properties of copper-coated graphite/copper composite was studied.The results show that the addition of copper-coated carbon fiber can effectively improve the mechanical properties and friction and wear properties of the composites.when the carbon fiber content is 1.5wt%,the hardness and bending strength of the composites reach the highest,which are 87HV and 145MPa,respectively.Reciprocating sliding friction and wear test results show that the friction coefficient of 1.5wt%copper-coated carbon fiber/copper-coated graphite/copper composite is more stable and the wear rate is the lowest,which is 3.56×10^-14mm³·m^-1·N^-1.In the friction process,the copper-coated carbon fiber plays the role of load bearing,inhibits the initiation and propagation of cracks,and acts synergistically with copper-coated graphite to form continuous carbon film,which effectively enhances the wear resistance of composites.（5）The effect carbon configuration（copper-coated graphite,copper-coated expanded graphite and copper-coated carbon fibre）on the friction and wear properties of was analyzed:copper-coated graphite and copper-coated expanded graphite improves the bonding between graphite and copper,and forms a three-dimensional network structure of copper in the material.The heat dissipation channel is provided during the friction process,and the damage to the friction film is reduced.In the modification of copper-coated graphite/copper composite,the carbon fiber plays an excellent mechanical property and improves the mechanical property of the composite.The continuous friction film is formed on the surface of the sample by the co-modification of copper-coated carbon fiber and copper-coated graphite,and the friction coefficient and wear rate of the composite are reduced.（6）The effect of copper configuration（copper powder,copper coating and copper foam）on the friction and wear properties of graphite/copper composites was analyzed:copper foam and copper coating reduce the separation effect of graphite on copper,a complete network structure is formed in the material,and effectively reduces the resistivity of the composites.The skeleton structure of copper foam is not easy to deform under load,which improves the plastic deformation resistance of the material.The oxide film formed on bare skeleton surface was closely bonded with matrix and not easy to fall off.In addition,the pores between the copper foam coatings can store the debris,which effectively reduces the friction and wear properties of the composites.