Fabrication And Performance Of Copper-coated Carbon Fiber/graphite-Cu Composites

Graphite-Cu composites is a type of widely used electrical contact materials.With the development of science and technology,higher performance of electrical contact materials was required.Therefore,development of high performance of graphite-Cu composites has drawn great attention in the field of copper-matrix composites.Three different types of graphite(flake graphite,colloidal graphite and copper-coated graphite)-Cu composites were fabricated via powder metallurgy technique.Effects of graphite type and content on the microstructures,density,resistivity,hardness and bending strength,as well as the friction and wear performance of target graphite-Cu composites were systematically studied and the corresponding mechanism was also proposed.Main achievements of this paper are as follows:With the increase of graphite content,microstructure of copper matrix in three different composites gradually transformed from the continuous net-structure into isolated blocky structure with different degrees of declining density,hardness and bending strength as well as growing resistivity.Among all three composites,with the same graphite content,copper-coated graphite-Cu composites has the lowest resistivity as well as the highest hardness and bending strength due to the enhanced wettability and interface bonding between the copper and graphite and the continuous network of copper matrix,while the colloidal graphite-Cu composites has highest resistivity as well as lowest hardness and bending strength due to the relatively higher splitting effect of colloidal graphite on the copper matrix.With 15 wt.% graphite content,both the flake graphite-Cu and the copper-coated graphite-Cu composites could meet the performance requirements of electric brush products,colloidal graphite-Cu composites couldn't meet performance requirements of the actual brush including the resistivity,hardness and bending strength.Under the same friction and wear conditions,copper-coated graphite-Cu composites has the highest friction coefficient and lowest wear loss is the lowest,while colloidal graphite-Cu composites is just the opposite.Carbon fibers were surface-coated with copper by pyrophosphate copper plating uniformly,and fully coated Cu-carbon composite fibers with remarkable conductivity could be obtained with optimized parameters,which could well solve the two main problems of “black heart” and “agglomeration” in the plating of long carbon fibers.In order to further improve the mechanical as well as the friction and wear performance of graphite-Cu composites,copper-coated carbon fibers were added to above three types of graphite-Cu composites,the effects of the addition of 1wt.% coppercoated carbon fibers on the microstructure,density,resistivity,hardness and bending strength of three types of graphite-Cu composites were investigated,the wear mechanism of the composites before and after the addition of copper-coated carbon fibers was also analyzed.The results showed that copper-coated carbon fibers uniformly distributed in the copper matrix and don't break the continuous network of copper matrix.Compare to three corresponding graphite-Cu composites,the density and resistivity of the copper-coated carbon fiber/graphite-Cu composites don't change obviously,while the hardness and bending strength increased.The as-fabricated copper-coated carbon fiber/colloidal graphite-Cu composites can achieve the performance requirements of electric brush products.Replacing the graphite by proper amount of copper-coated carbon fiber can to a certain extent increase the friction coefficient of the target coppercoated carbon fiber/graphite-Cu composites and reduce the wear under the same test conditions.During rolling wear,surface defects of graphite-Cu composites are mainly composed of pits and furrows.The wear form includes adhesive wear,abrasive wear,peeling wear and oxidation wear.After the addition of copper-coated carbon fibers,the solid lubrication film became relatively rough with certain amount of abrasive particles.