Fabrication And Properties Of Graphene/Copper Composites With Micro-Layered Structure

With the development of modern science and technology and high-tech industries,higher requirements are imposed on the properties of copper and copper alloys.For example,integrated circuit lead frames and plug-and pull electrical contact materials require the materials have tensile strength greater than 600 MPa and good electrical and thermal conductivity.The mechanical properties of materials in these fields have become the main factor.However the strengths of current discontinuous sheet graphene/copper composites are usually between 300-400 MPa,which are still far from practical requirements and need to be improved.This paper takes the field of integrated circuit lead frames and plug-and pull electrical contact materials as the application background,and aims to improve the mechanical properties of discontinuous sheet graphene/copper composites,obtain good electrical and thermal conductivity at the same time and provide technical support for the practical application of such materials.This paper proposes two solutions: molecular-level mixing self-assembly method and in-situ growth-composite method,hoping to improve the strength and toughness of graphene/copper composites by constructing layered structures.In order to obtain graphene/copper composites with high strength and good comprehensive performance,based on the traditional molecular-level mixing and self-assembly methods,a preparation method of graphene/copper composites with multi-layered structure was developed in this paper.The graphene in this method is reduced graphene oxide(RGO)made from a top-down approach.It was found that in the molecular mixing process,under the conditions that p H value is 13.6 and temperature is 20 ?,the composite powder could form multi-layered structure by self-assembly.In addition,the volume fraction and chip diameter of graphene have important effects on the structure and properties of the composites.The tensile strength of the graphene/copper composite with a volume fraction of 2.5% was 748 MPa,and its electrical conductivity and thermal conductivity reached 65.7% IACS and 308 W/(m?K)respectively.In view of the disadvantages of complicated preparation technology,high cost and high equipment requirements for graphene/copper composites,this paper also proposed a very simple in-situ growth-composite method to produce graphene/copper composites with excellent comprehensive performance.Using commercial copper powder coated with oleic acid anti-oxidation coating as raw material,during the sintering process,the catalytic properties of copper were utilized to transform oleic acid into graphene nanosheet(GNS)in situ by bottom-up approach,and the densification of composite powder was realized at the same time.Compared with other preparation methods,this method can prepare graphene/copper composites in one step,which greatly simplifies the process and equipment requirements.It was found that the particle size of the original copper powder had an important influence on the quality of graphene.With the decrease of the particle size of the original copper powder,the contact area between the oleic acid layer and the copper increased,so that the oleic acid layer was catalyzed by more copper surface,and the quality of graphene generated increased.The maximum tensile strength of the 0.49 vol.% graphene/Cu composite prepared with particle size of 300 nm copper powder is 503 MPa,and the apparent enhancement coefficient Ra is 392.The composite material also has excellent electrical and thermal conductivity properties,with electrical and thermal conductivity of 77.8% IACS and 365 W/(m?K)respectively.In order to further improve the mechanical and electrical properties of composite materials,strengthen the basic research on the forming technology of composite materials,and meet the requirements of the practical application of composite materials,this paper carried out rolling deformation of RGO/Cu and GNS/Cu composite materials,and studied the effects of rolling ratio and rolling temperature on the structure and properties of composite materials.The increase of rolling ratio can refine the matrix grains and improve the dispersion uniformity of graphene in the composites.At the same time,the microcracks in the matrix at the beginning of rolling healed with the increase of rolling ratio.As a result,the tensile strength and elongation of cold-rolled composites with high rolling ratio were greatly improved.With the decrease of rolling temperature,the tensile strength of composites increases.The elongation of RGO/Cu and GNS/Cu composites with a deformation of 85% at room temperature was significantly improved compared with sintered composites,reaching 8.8 % and 9.3 %,respectively.The tensile strength was kept at a high level,666 MPa and 548 MPa respectively.In addition,both high rolling ratio and high rolling temperature contribute to improving the electrical conductivity of RGO/Cu and GNS/Cu composites.The electrical conductivities of RGO/Cu and GNS/Cu composites rolled at 500 ? with rolling ratio of 85 % reached 81.8% IACS and 85.2% IACS respectively.