Research On The Fabrication,structural And Properties Of Carbon Nanotubes/Graphene Reinforced Cu Matrix Composite

Applications such as special electric brushes,overhead conductors for high-speed railways and sliding contact materials require copper matrix composites not only with excellent electrical and mechanical properties,but also with good frictional wear properties.Carbon nanotubes(CNTs)and reduced graphene oxide(RGO)are considered as the ideal reinforcements for copper matrix composites because of their excellent mechanical,electrical and wear reduction properties.The preparation and production of high performance CNTs and RGO reinforced copper matrix composites needs to overcome such technical problems as the poor dispersion uniformity and the low interfacial bonding strength of the reinforcements.In this thesis,molecular level mixing(MLM)and matrix powder flake method were used to investigate the pretreatment process of the reinforcements and the effect of reinforcement content and preparation process parameters on the microstructure and properties of the composites.It provides a theoretical basis and a realization pathway for the preparation of high performance CNTs/RGO reinforced copper matrix composites.The main research results are as follows.(1)It investigated the effects of sintering temperature and CNTs content on the microstructure and mechanical properties of CNTs/Cu composites.Results have shown that the MLM method could improve the dispersion uniformity of CNTs,and the addition of CNTs could refine the matrix grains.When the CNTs content was in the range of 0～2.0 vol.% and the sintering temperature was below 800 °C,there was a positive correlation between the mechanical properties of the composites and the content and temperature of CNT.(2)It has explored the effects of chemical cracking process parameters on the microscopic morphology of CNTs and the effects of the state and content of cracked CNTs on the mechanical properties of the PUCNTs/CuCr composites.Chemical cracking can strip CNTs into "willow-like" cracked CNTs(PUCNTs),which helps to increase the interfacial contact area between PUCNTs and CuCr matrix and to promote the generation of interfacial chromium carbide,thus improving the load transfer efficiency of PUCNTs and the mechanical properties of the composites.The improvement in strength is mainly attributed to the load transfer reinforcement of PUCNTs and the improvement of interfacial shear strength by interfacial chromium carbide.(3)It investigated the effects of graphene acidification treatment and its content quantity on the microstructure and mechanical properties of RGO/CuCr composites.The acidified graphene is easier to be dispersed evenly in the composites and plays a role in refining the grains of the CuCr matrix.The main strengthening mechanisms of RGO/CuCr composites are load transfer strengthening and dislocation strengthening,among which load transfer strengthening contributes the most to the improvement of yield strength of the composites.Meanwhile,it investigated the effects of cold pressing deformation and annealing temperature on the microstructure and mechanical properties of RGO/CuCr composites.The cold pressing deformation can induce the tendency of RGO to be oriented along the vertical deformation direction,and demonstrate the cellular substructure characteristics of CuCr matrix.With the increase of annealing temperature,the microstructure of CuCr matrix has gone through a process of changes,from revert substructure organization,revert substructure to recrystallized organization and recrystallized organization in order.(4)It investigated the formation and evolution of lubricating films on the wear surfaces of PUCNTs/CuCr and RGO/CuCr composites and the effects of reinforcement content and friction load on the frictional wear performance.With the same load,a positive correlation was found between the PUCNTs and RGO content and the lubricating film coverage and frictional wear performance.As the load increased,there was a negative correlation between the frictional wear performance of the PUCNTs/CuCr and RGO/CuCr composites and their load.The physical model of the friction coefficient has demonstrated that there was a positive correlation between the friction coefficient of RGO/CuCr composites and the experimental load,which explains the effect of load on the friction coefficient of the composites quantitively.In this thesis,three composites were successfully prepared,and the microstructure and cold pressing deformation behavior of the composites were investigated in depth using advanced characterization techniques to elucidate the strengthening mechanism of the composites,providing a theoretical reference for the technical route to develop high-performance CNTs/RGO reinforced copper matrix composites.This thesis contains 121 figures,8 tables and 208 references...