Investigation On Interface Modification And Mechanical Properties Of Graphene/Cu Composites

Graphene,with utra-high elastic modulus,strength and electrical/thermal conductivity,has a great application potential in the field of metal matrix composites?MMCs?.However,the poor interfacial bonding is the key problem restricting the development of graphene/metal composites.This thesis utilized the two strategies of carbide-coating?Mo₂C?and matrix-alloying?Cr-aloying?to improve the interfacial bonding of graphene/Cu composites.The composites were prepared by flake powder metal urgy.The interface structures,which involved interface morphology,interface products,interface crystal ographic relation,as well as dislocation density and distribution at interface,were systematically investigated.The effect of interface structures on the mechanical behavior of the composites were also studied.The main results are as follows:?1?Mo₂C nanoparticles grown on reduced graphene oxide?Mo₂C@RGO?were used to prepare the Mo₂C@RGO/Cu composites.The Mo₂C nanoparticles played a bridging role in not only being firmly attached on RGO but also forming a semi-coherent interface with the Cu matrix,leading to strong interfacial bonding of the composites.The yield strength?YS?and ultimate tensile strength?UTS?of 1 vol%Mo₂C@RGO/Cu composites were 238 and 292 MPa,which were 26%and 57%higher than those of 1 vol%RGO/Cu composites,respectively.The significantly enhanced strength in Mo₂C@RGO/Cu composite was attributed mainly to the Mo₂C-induced robust interface.The strengthening mechanism of Mo₂C@RGO/Cu composite was proposed to be highly dependent on the dual role of Mo₂C nanoparticles that not only enhanced the load transfer strengthening of RGO??85%?but may also provide the Orowan strengthening themselves??15%?.?2?The RGO/CuCr composites were prepared by matrix aloying with addition of trace⁰.18 at%Cr in the Cu matrix.In the sintering process,a trace amount of Cr₇C₃layers/nanoparticles were found to be in-situ generated at the RGO-CuCr interface,which transformed the RGO-CuCr interface into two sub-interfaces of CuCr-Cr₇C₃ and Cr₇C₃-RGO.The coherent/semi-coherent bonding was generated at the CuCr-Cr₇C₃ interface,and the combined coherent/incoherent bonding and interface distortion area were generated at the Cr₇C₃-RGO interface.Both contributed to the improved interfacial bonding of RGO/CuCr composites.The 2.5 vol%RGO/CuCr composite exhibited a YS of 267 MPa and a UTS of 352MPa,which were 82%and 19%higher than those of 2.5 vol%RGO/Cu composites,respectively.The enhanced strength of RGO/CuCr composites was directly linked to the dual role of Cr₇C₃ layers/nanoparticles that not only improved the load transfer efficiency,but also promoted the dislocation strengthening ability of RGO itself.A possible Cr₇C₃formation/evolution mechanism was proposed that involved the four steps of amorphous carbon?AC?formation,Cr₇C₃ nucleation in AC,Cr₇C₃ growth and Cr₇C₃ coalescence.The relatively low?953 K?and high?1153 K?sintering temperatures resulted in the generation of Cr-diffused AC layer and large islandshaped/rod-shaped Cr₇C₃ nanoparticles at the interface of RGO/CuCr composites,respectively.Both led to the unsatisfied mechanical properties of RGO/CuCr composites.The medium sized Cr₇C₃ layers/nanoparticles?10-30 nm?formed at 1053 K led to the highest strength of RGO/CuCr composite with a satisfactory strength-ductility combination.