Fabrication Of Graphene Reinforced Copper Matrix Composites For Application As Electrical Contacts

Copper matrix electrical contact materials are widely used as electrical switches,electronics,relays,and high-voltage circuit breakers.The safe operation,costs of electrical switches and transmission lines,rely on the reliability and service life of electrical contact materials.Therefore,the development of copper matrix electrical contact materials with high-performance and long-servicelife,is of great significance to maintaining the safe and safe operation on electrical appliances.At present,the added secondary phase materials such as alloying elements（Ti,Ni,Cr,etc.）,carbides（Si C,B₄C,WC,etc.）and other additives with high work function and high melting point（Y₂O₃,Al₂O₃,graphite,etc.）,It is the main method to improve the service life of copper-based electrical contact materials.However,the electrical conductivity and thermal conductivity of these additive phases are much lower than pure copper.The electrical conductivity and thermal conductivity of the copper matrix composite material will decrease inversely with the increase of the additive content.Therefore,it is still challenging to design and construct reinforced copper matrix electrical contact composites without reducing electrical and thermal conductivity.Graphene has excellent electrical,thermal properties,self-lubrication,and good mechanical strength due to its unique two-dimensional crystal structure.The discovery of graphene and the progress of mass production laid the foundation for its application in the field of copper matrix electrical contact composite materials.Under the action of van der Waals force,graphene is easy to form agglomeration,which increases the difficulty of its dispersion;due to the poor interfacial wettability of graphene and copper matrix and the large density difference between the two,graphene is prone to high temperature processes.As it floats on the surface of molten copper,it is difficult for graphene to be homogeneous distribution in the copper matrix,which affects the overall performance of the composite material.For graphene modified copper matrix electrical contact materials,how to reasonably control the distribution of graphene in the metal matrix and ensure the density of the composite are the key points to maintain the electrical and thermal properties.In addition,how to improve the interfacial bonding between the graphene and the copper matrix towards hig-performance composite can is also the focus of research.Based requirements on service life and stability of copper matrix electrical contact materials,as well as the demand on the wear resistance and arc ablation resistance,this work combine the uniform dispersion and formation of strong interfacial bonding,aiming to fabricate high-performance and long-life graphene copper matrix electrical contact composite materials.This work also studied the relationship between different fabrication processes,graphene derivitive,component content and the performance of the composite materials as electrical contact.The arc ablation resistance enhancement mechanism of graphene was explored.The research content of the thesis includes the following three aspects:（1）We have designed a scalable method for in-situ synthesis of graphene reinforced copper matrix composites（Gr/Cu）.The Gr/Cu composites,with ultralow-content homogenous graphene in copper grains boundaries,are directly fabricated by in-situ AP-Jet-PECVD and hot pressing.Comparing to pure copper,the thermal conductivities of Gr/Cu composites are enhanced by 7.8%with ultralow content of graphene,which can be attributed to the interconnected graphene network in the matrix.Besides,the coefficient of friction and wear rate of Gr/Cu composites in contact with GGr15 steel balls are only 0.08 and 3.0×10^-4 mm³ N^-1 m^-1,which is merely 17.8%and10.1%of pure copper,respectively.The breakdown voltage strength and arc ablation resistance of C2.0 Gr/Cu composite bulks can be significantly enhanced by 107%and33%,respectively,due to the lightnting-rod effect of multilayer graphene with sharp edges and higher work function,thus offering promising application as high voltage electrical contacts.（2）.Combining the high temperature catalysis of the space-limited metal surface with the powder metallurgy process,a graphene-copper composite material with a core-shell structure is in-situ fabricated.The nanocellulose gel is coated on the surface of the spherical copper powder,and then annealed at a high temperature in a mixed atmosphere of hydrogen and argon to prepare graphene-like copper composite powder,which is then sintered and molded by a vacuum hot pressing process.Compared with pure copper,this method has a longer service life of electrical contact.However,the decline in electrical,thermal conductivities and mechanical properties limits its further application.The study verified the feasibility of surface modification strategy on copper particles to improve the electrical contact performance of copper matrix electrical contact materials,laying the foundation for subsequent research.（3）.We develop a scalable method based on surface modified strategy for the synthesis of high-quality graphene nanoplatelets encapsulated monodispersed copper particles,followed by vacuum hot pressing to fabricate graphene reinforced copper matrix composites.Compared with the reported method,this surface modification process is more efficient for industrial-scale mass production.Comparing to the pure copper,the tensile strength and yield strength are enhanced by 19%and 71%respectively,owing to the enhanced dislocation density around Cu-graphene boundary.Besides,lower friction coefficient and enhanced wear resistance can be simultaneously achieved in our GNPs/Cu composites.For the real electrical contact performance test,the service life of electrical contacts made of graphene reinforced copper matrix composites,is 10 times longer as that of the commercial pure copper electrical contacts and almost comparable to Cu Ag20 contacts,demonstrating its superior ability to solve the electrical contact issues in electrical engineering systems.