Fabrication And Properties Of Short Mesophase Pitch-based Graphite Fiber/copper Composite

Carbon fiber(CF)reinforced Cu composites are considered promising materials applied in the fields of aviation,aerospace,electronics,semiconductor and many other fields because of their outstanding properties of conductivity,thermal conductivity(TC),antifriction,wear resistance,and low thermal expansion.With the advancement of graphite fiber technology,the MPGFs can offer a high thermal conductivity in excess of 850 W/m·K,a low resistivity(about 1 ×10-4??·cm)and a negative CTE which makes the application of copper-matrix composites reinforced by it has greater potential.In this paper,the mesophase pitch-based graphite fibers and Cu are used respectively as the reinforcing and matrix material to prepare short graphite fiber/Cu composite by electroless copper plating and the twice cold-pressing sintering.The surface morphology and composition of the composites were characterized by scanning electron microscopy-energy dispersive spectrometer(SEM-EDS)and X-ray diffraction(XRD),the resistivity,density,porosity,thermal conductivity and other properties were also analyzed.The effects of pretreatment,bath temperature,pH value,initial concentration of formaldehyde and loading capacity on the electroless copper plating were investigated.The effects of molding methods,molding pressure,sintering temperature and holding time on the properties of the composites were also investigated.The main conclusions are described as follows:(1)The roughness and number of O functional groups on the fibers surface were increased after pretreatment,it could greatly improve the efficiency and quality of electroless copper plating on MPGFs.(2)During the electroless copper plating on the pretreated MPGFs,all of bath temperature,pH value,initial concentration of formaldehyde and loading capacity have a lot of influence on the plating rate of copper and the quality of Cu players.The bath temperature,pH value,initial concentration of formaldehyde and loading capacity was 60?,13.0,15mL/L and 2g/L respectively corresponding to the optimized electroless copper plating process.The MPGFs was overlaid a complete,uniform,dense and highly purified Cu coating using this process.The resistivity of copper-coated MPGFs decreased to 7.52??·cm from 131.19??·cm.The results of the binding performance test showed that the copper-plated MPGFs had good stability.(3)The Cu-coated MPGFs was used to prepare short graphite fiber/Cu composite directly by the twice cold-pressing and twice sintering method,the distribution of fibers in Cu matrix was more uniform,the pores were smaller and the overall performance was more excellent than the composite made by the traditional method.Among them,the relative density and the thermal conductivity increased by 41.0%and 167.4%respectively,the resistivity decreased by 83.2%.After the second pressing and sintering,the bulk density and the thermal conductivity of the composites increased by 5.1%and 11.6%respectively,and the resistivity decreased by 46.2%.(4)In the process of cold-pressing sintering,the molding pressure,sintering temperature and holding time have great influence on the microstructure and properties of the composites.With the increase of molding pressure,the relative density of the composite increased first,then decreased and increased again in the end,the change trend of the thermal conductivity was about the same as the density,and the resistivity had opposite change tendency.The relative density and the thermal conductivity of the composites increased at first and then decreased with the increase of the temperature or the prolonging of holding time,while the resistivity was opposite from the above.(5)The short MPGFs reinforced copper matrix composites with excellent properties were prepared under the conditions of molding pressure,sintering temperature and holding time was 450MPa,900? and 3h respectively.The relative density was 95.2%,the thermal conductivity reached 228.13W/m K,the resistivity was as low as 31.25??·cm,the thermal expansion coefficient and hardness was 4.67×10-6/K and 47.3HV respectively,and the composites was isotropic in the plane that was perpendicular to the pressing direction.