| Copper,as a kind of metal with metallic luster,has good electrical and thermal conductivity as well as good ductility,but its poor strength limits its potential application.Enhancing the strength of metals through microstructure engineering is of crucial importance for the development of structural materials.The key factor that determines the strength of the metal is how effectively dislocation motion can be hindered.The well-known Hall-Petch relationship describes how polycrystalline metals become stronger as grain size is reduced.In this paper,we use cu nanoparticles(NPs)as original material and introduce graphene to enhance cu matrix.Graphene is a single-atomic-layer material with excellent mechanical properties and has the potential to enhance the strength of composite.Graphene has the highest-known intrinsic strength of 130 GPa and a Yong's modulus of 1 TPa.It also has the well-known electrical properties,including a mobility of 15,000 cm2V-1S-1,which make graphene as an outstanding candidate for matrix nanofiller.Previous reports about Cu/graphene composites mainly based on reduced graphene oxide(rGO).As well known,rGO contains a large amount of oxygen groups which would fade graphene intrinsic properties including strength and conductivity etc.Moreover,for rGO based composites,how to disperse graphene homogenously into Cu matrix is a key factor for enhancement.In this paper,we grow graphene on the surface Cu NPs directly.Chemical vapor deposition is one of the most promising approaches to fabricate large-scale high-quality graphene.After growth,high-quality graphene is grown on the surface of Cu NPs.Finally we use powder metallurgy method to consolidate the NPs to Cu matrix.The Vickers hardness,electrical conductivity,wear resistance property as well as oxygen resistance property are tested.The conclusions are listed as follows:(1)MgO NPs are introduced to isolate Cu NPs at high temperature(1050?)?The as-grown graphene is multilayered with high quality proved by Raman spectrum.Scanning Electron Microscope and Energy Dispersive Spectrometer analysis indicate the Cu NPs are fully covered by graphene without oxidization,which is mainly due to the impermeability of graphene.TEM images show the number of graphene layer is more than 5,which is reported firstly.The mechanism is proposed that the growth area is confined to a few hundred nanometers,so C atoms and intermediate can attach to Cu surface to grow graphene constantly.(2)The Vickers hardness of graphene/Cu composite and pure Cu are 2.53 GPa and 1.01 GPa,respectively,so the hardness is improved to approximately 2.5 times than that of pure Cu.The electrical conductivity of composite is nearly equal to that of pure Cu,at 1.72×10-6 ?-cm and 1.69×10-6 ?-cm,respectively.The superior shear modulus of graphene can block dislocations slipping across the boundary effectively and finally improve the hardness.The addition of graphene doesn't deteriorate the conductivity of matrix ascribed to the excellent intrinsic conductivity of graphene.(3)The coefficient of frictions of composite and pure Cu are 0.2 and 0.35,respectively,when using the alloy ball as the friction pairs and the corresponding wear rates are 2.8×10-5 mm3/ N· m and 379.4×10-5 mm3/ N· m,respectively.The COF reduced by 57% and the wear rate decreased by two orders.The tribological mechanism is proposed that graphene forms a layer of tribofilm on the surface of Cu matrix,which avoids the direct connection between Cu and alloy ball.During the friction process,the energy loss greatly reduced due to the very low surface energy of graphene.After exposing to the oxidizing aqueous solution of H2O2 for 24 hours,the composite shows only the surface is oxidized while for pure Cu,the whole matrix is oxidized severely,so the graphene can prevent the matrix from oxidization. |
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