Study On The Preparation And Properties Of Graphene Reinforced Copper Matrix Composites

The electric connecting clamp is a metal accessory used to fix the high-voltage transmission line of high-speed rail transit,which plays the role of connecting and transmitting current in work.The electric clamp is subject to high times of current and off-line arc burning loss in operation,and has been exposed to the natural environment for a long time,so it is required to have great conductivity、arc burning resistance、high strength、corrosion resistance and other service characteristics.At present,nickel silicon bronze is widely used as the material of electrical connection clamp.However,with the rapid development of rail transit in recent years,higher requirements are put forward for the material of electrical connection network.The low conductivity of nickel silicon bronze is difficult to meet the design requirements of today’s high-speed.In order to improve the conductivity of nickel silicon bronze,it is necessary to reduce the content of alloying elements in the material.However,when the content of alloying elements decreases,the strength of nickel silicon bronze decreases significantly.Therefore,it is urgent to develop copper matrix composites with high strength,high conductivity and arc corrosion resistance to replace nickel silicon bronze electrical connector.Graphene,as a new two-dimensional carbon material,has been concerned and studied as a reinforcement of copper matrix composites due to its ultra-high thermal transmission properties,mechanical properties and chemical stability.It is expected to make progress in the application of electrical contact,electronic packaging materials,corrosion-resistant conductors and other fields.However,the wettability of the interface between graphene and copper is poor,the uniformity of dispersion in the matrix is not high,and its ultra-high specific surface area makes graphene easy to agglomerate.These shortcomings greatly reduce the performance of graphene copper matrix composites and limit its application.In this paper,the problem of interfacial adhesion and dispersion between graphene and copper was solved by depositing graphene on the foam porous copper by chemical vapor deposition（CVD）.The graphene reinforced copper matrix composites were prepared by vacuum hot pressing sintering,and the microstructure and properties of the composites were explored in order to provide a scientific reference for the preparation technology of new electrical connector materials.In this paper,the deposition of graphene and the sintering process of the composites were investigated.The graphene was coated on the surface of the foam copper skeleton by adjusting the deposition time.The graphene was characterized by SEM、EDS、XRD and Raman.The graphene particles were obtained by etching the copper matrix.It was observed that the graphene particles deposited had relatively large area size,high degree of crystallization and good continuity.After the deposition of graphene,the foamed copper graphene compound was obtained.In this paper,the graphene copper composites were prepared by vacuum hot pressing sintering.The composite materials were obtained by direct folding heating copper foam compound and filling copper powder into the foam copper gap,and then hot pressing two kinds of composites.Compared with the two schemes,the properties of the composite material were obtained.The density of the composites decreased with the increase of graphene deposition content of 0、0.05 wt.%、0.1 wt.%、0.2 wt.%and 0.4wt.%.With the increase of deposition graphene content,the interface defects of composite materials prepared by filling copper powder after direct hot pressing with foam copper are less.The electrical conductivity,thermal conductivity,tensile strength and hardness of the composites under the two schemes were compared and analyzed.With the increase of the deposition content,the resistivity of the composites increased and the conductivity decreased significantly from 72.4%IACS to 57.5%IACS.The electrical conductivity of the composites after hot pressing sintering was first increased and then decreased.The maximum conductivity of the composites was 86.2%IACS when the graphene content was 0.2 wt.%.The change trend of thermal conductivity is consistent with the electrical conductivity trend.The thermal conductivity of composites prepared by direct hot pressing sintering of foam copper is reduced from 262 W/（m·K）to 143 W/（m·K）,and the thermal conductivities is lower than that of pure copper at the same condition.However,the thermal conductivity of the 0.2wt.%composites filled with copper powder after hot pressing is 313 W/（m·K）,which is 19.5%higher than that of pure copper under the same conditions.The maximum tensile strength of the composites filled with copper powder under the same hot pressing condition is 338MPa,while the maximum tensile strength of the composites directly heated by foam copper is only295MPa.The maximum yield strength of the two kinds of composite materials is 214MPa and125MPa respectively.The fracture analysis shows that the fracture mode of direct hot pressing is ductile to brittle compared with that of the filler metal powder.Compared with pure copper,the highest hardness of direct hot pressing and filled copper powder hot pressing composites increased by 5.4%and 55.1%,respectively.In summary,the properties of composites fabricated by hot pressed copper filled powder are all higher than those of direct hot pressing.Therefore,the hot pressing sintering of graphene copper foam filled with copper powder is the best composite material forming scheme and has higher performance.The composites prepared by the best molding scheme were tested in sodium chloride solution.Compared with pure copper,the effect of graphene deposition on the corrosion resistance of the composites were explored.The open circuit potential of the composites is higher than that of pure copper,which indicates that graphene can reduce the corrosion tendency of the composites.The polarization curves show that the composites with 0.1 wt.%and 0.2 wt.%deposition content can more effectively alleviate the dissolution of matrix copper and reduce the corrosion sensitivity,and the corrosion potential and corrosion rate of the composites with 0.1 wt.%deposition content are-0.213V and 9.20×10^-8Acm^-2,respectively.The impedance Bode diagram also shows that the corrosion resistance of the composites with 0.1 wt.%and 0.2 wt.%deposition content is better,and the corrosion resistance of the composites with 0.1 wt.%graphene is the best.