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

With the rapid development of modern industry,people have put forward high strength and high conductivity requirements for copper-based materials used in several fields,such as electrical,mechanical engineering,railway transportation,aerospace and other areas.As an emerging two-dimensional carbon nanomaterial,graphene is regarded by relevant scientists as the most ideal reinforcement phase for copper-based composites due to its ultra-high electrical and thermal conductivity and superior mechanical properties.In recent years,although a lot of work has been carried out in the field of graphene reinforced copper composite material,there still exist some difficulties to be solved.For example,graphene is easy to agglomerate,which makes it challenging to achieve its uniform dispersion within the copper matrix,poor wettability and no chemical reaction between graphene and copper matrix,and the interfacial connection between them can only be achieved by mechanical occlusion.These problems seriously weaken the enhancement of copper matrix by graphene.To solve the above issues,chemical vapor deposition(CVD)was used to generate graphene in situ on the surface of copper foam matrix to achieve uniform dispersion of graphene within the copper matrix and form a good interfacial bond with the copper matrix.Graphene-reinforced copper matrix composites were prepared by two different molding methods.It aims to provide a scientific reference for the preparation technology of high-strength and high-conductivity copper-based contact materials.In this thesis,the chemical vapor deposition process of graphene was investigated.Graphene films were prepared on the surface of copper foam substrate by adjusting two factors,methane to hydrogen gas flow rate ratio and deposition time.By analyzing and comparing the Raman spectroscopy test results and electron scan photographs of graphene under different deposition parameters,the optimal graphene vapor phase deposition parameters were determined to be 20 sccm for methane gas flow rate,30 sccm for hydrogen gas flow rate,150 sccm for argon gas flow rate,1000 °C for deposition temperature and 15 min for deposition time.The graphene film with the optimal deposition process parameters was obtained by etching to remove the substrate.The results of its Raman spectroscopy tests show that the graphene layer prepared under this parameter is less in number and of good quality with high-quality structural integrity.It was observed by electron scanning that the few-layer graphene prepared at this parameter was less self-supporting,but the larger area was able to cover the surface of the copper foam substrate completely.The generated graphene film adheres to the copper foam substrate to form a graphene-copper foam composite with a complete three-dimensional skeleton structure,which is the key to achieving a uniform graphene dispersion within the copper substrate.The pores of the graphene-copper foam composite were filled with copper powder.Then the graphene-reinforced copper matrix composites were prepared by two different forming processes: cold-press sintering-cold-roll annealing and vacuum hot-press sintering.Mechanical and electrical conductivity tests and microstructure characterization were performed on the composites prepared by the two forming processes.For the composite prepared by the cold pressing sintering-cold rolling annealing process,the material was gradually densified with the increase of rolling times.The composite’s relative density after the second rolling reached 98.96%.No agglomerated graphene was found by optical microscope observation of its microstructure.Compared with pure copper prepared under the same parameters,it can be seen that the addition of graphene has the effect of refining grains.The interfacial bonding between graphene and the applied copper powder was strengthened by increasing the number of rolling.The addition of graphene had a significant strengthening effect on the mechanical properties of the copper matrix while maintaining its high electrical conductivity.The composites prepared by cold-press sintering and secondary cold-rolling annealing showed tensile and yield strengths of 289.5 MPa and 114.6 MPa,which were32.98% and 64.18% higher than those of pure copper while maintaining 88.7% IACS high electrical conductivity.For the composites prepared by hot-pressing sintering,a relatively complete graphene skeleton was found by electronic scanning observation of the microstructure,indicating that the three-dimensional skeleton structure of the graphene-copper foam composite was not damaged during the sintering process.Only a few amounts of graphene were pulled out during the material fracture process,showing that the interface between graphene and the applied copper powder was well bonded.The tensile and yield strengths of the composites prepared by vacuum hot-press sintering were 356.7 MPa and 197.6 MPa,which were 63.84%and 183% higher than those of pure copper,while the electrical conductivity reached 85.8%IACS.The composite material prepared by the hot-pressing sintering method meets the application requirements of the new type of electrical connection clip.