Preparation,Microstructure And Mechanical Properties Of Copper Matrix Composites Reinforced By Graphene Materials

Metal matrix composites reinforced with graphene have shown great potentiality in many industrial applications owing to their excellent mechanical properties,electrical and thermal conductivity,and wear resistance.However,some key problems including graphene dispersion,interface bonding and graphene structural integrity impede the development of the composites.Moreover,owing to the anisotropy of graphene,aligning graphene in the matrix may further improve comprehensive properties of the composites in the particular direction.To well understand and sovle these problems,copper matrix composites reinforced with kinds of graphene derivatives were prepared by liquid processing method including semi-powder method and molecular-level mixing（MLM）process in this study.The effect of chemical surface modification on dispersion of graphene nanoplatelets（GNPs）and interface bonding between GNPs and Cu matrix was studied.The changes of microstructure,mechanical properties and strengthening mecahnisms caused by different graphene materials（GNPs,Ni-GNPs,RGO）were comparatively discussed.The interface structure of graphene/Cu composites prepared by MLM process was investigated from a new perspective.Furthermore,applied magnetic field was adopted to align Ni-GNPs in the Cu matrix.The results are as follows:1.Copper matrix composites reinforced with GNPs,Cu-GNPs and Ni-GNPs were prepared by semi-powder method.GNPs contacted in direct and were agglomerated subsequently in the Cu matrix when adding GNPs directly.Voids and microcracks formed at interface between GNPs and Cu matrix.After chemical modification,Cu and Ni particles adsorbed on the GNPs surface acted as barriers for keeping GNPs from direct contact.The strength of composites decreased with the increase of the GNPs content,but first increased then decreased with the increase of the modified GNPs content from 0 to 1.0 vol.%.Tensile strength of 0.5 vol.% Cu-GNPs/Cu and 0.7 vol.% Ni-GNPs/Cu reached 258 and 286 MPa,higher than the composites with same GNPs content.Thermal mismatch and load transfer were principal strengthening mechanisms,and grain refinement strengthening was secondary.2.Graphene materials were tightly bonded with Cu matrix in the composites prepared by MLM process.When the content below 0.5 vol.%,GNPs and Ni-GNPs were uniformly distributed.But agglomeration occurred with the content further increased.RGO showed better dispersibility than GNPs and Ni-GNPs.No obvious agglomeration was found in the composites with 0¹.0 vol.% RGO.GNPs and Ni-GNPs showed better strengthening effect below 0.5 vol.%,while RGO performed better from 0.5¹.0 vol.%.Thermal mismatch and load transfer were principal strengthening mechanisms for uniform GNPs and Ni-GNPs,and Orowan and load transfer strengthening were main for RGO.3.GO was pretreated with different reductant to get RGO with different sturcture.Cu matrix composites reinforced with different RGO(RGO_HCl,RGONa OH,RGO_N2H6O)were prepared by MLM process.RGO_HCl and RGO_NaOH showed strengthening and toughening effect on Cu matrix,while RGON2H6 O only showed excellent strengthening effect.RGO_HCl and RGO_NaOH contained many wrinkles and some epoxy groups C-O-C.When good interface bongding formed between RGO and Cu matrix,load would transfer from matrix to RGO during plastic deformation.Accordingly,wrinkles were straightened and C-O-C was bended,generating an extra yield effect to improve the elongation.RGO_N2H6O showed small size,few wrinkles and no C-O-C bonds,which was accounted for the different strengthening effect compared with RGO_HCl and RGO_NaOH.4.The interface between graphene materials and the matrix was first investigated at two different directions,namely graphene in-plane/Cu（Dp）and graphene edges/Cu（De）.For composites prepared by MLM process,interface of GNPs/Cu was mechanical bonding at Dp and metallurgical bonding at De;interface of Ni-GNPs/Cu was infiltration bonding at Dp and infiltration/diffusion bonding at De;interface of copper matrix reinforced with different RGO was all metallurgical/oxygen-mediated bonding both at Dp and De.5.Ni-GNPs were successfully aligned in the Cu matrix through an external magnetic field.The tensile strength,electrical and thermal conductivity of aligned Ni-GNPs/Cu composites was improved along the direction of magnetic field.The electrical and thermal conductivity of 0.2 vol.% Ni-GNPs/Cu composites were 111.08%IACS and 370.31 W/m?k,which were 23.08% and 19.85% improvement compared with sintered bulk Cu,and the tesile strength was improved by 8.84%.But high-content Ni-GNPs agglomerated resulting in the decrease of tensile strength.The next step is to disperse graphene uniformly during the preparation process of Cu matrix composites reinforced with aligned graphene.