Study On The Preparation,Microstructure And Properties Of CNTs-Fluid Reinforced Cu Matrix Composites

Metal matrix composites（MMCs）are widely used in aerospace,electronic,electrical,and mechanical engineering fields due to their excellent material properties.Copper（Cu）matrix composites are particularly promising because of their good electrical conductivity,thermal conductivity,and ductility,and the development of high strength and high conductivity copper matrix composites has become a recent hot spot.Carbon nanotubes（CNTs）possess outstanding mechanical properties,high axial electrical and thermal conductivity,and are ideal reinforcements for Cu-based composites.However,achieving uniform dispersion of CNTs and controlling their spatial distribution in Cu-based composites has been challenging.Furthermore,the interface between CNTs and Cu tends to have poor infiltration and weak bonding,leading to unsatisfactory mechanical and electrical properties of the composite.To address these issues,this paper presents a systematic research study aimed at improving the preparation and performance of carbon nanotube-reinforced copper matrix composites（CNTs/Cu）.In this paper,various approaches were taken to improve the dispersion uniformity of carbon nanotubes（CNTs）in a copper matrix.Firstly,the surface of acidified CNTs was chemically grafted using an ion exchange method to prepare CNTs-fluid.This allowed for better dispersion of the CNTs within the fluid.Subsequently,CNTs-fluid/Cu composites were prepared by utilizing a combination of powder metallurgy and molecular blending methods.This achieved a homogeneous dispersion of high levels of CNTs（with a mass fraction of 1wt.%）in the Cu matrix.Furthermore,to address the issue of weak interfacial bonding between the CNTs and the Cu matrix,trace amounts of nano-sized titanium（Ti）particles were introduced into the Cu matrix.This addition promoted a suitable reaction between the CNTs and Ti,leading to improved interfacial bonding strength and enhanced coordination between the CNTs and Cu matrix during deformation.As a result,the strength and plasticity of the composites were improved,mitigating the problem of significant plastic mismatch in CNTs/Cu composites.Finally,the electron transport at the interface of SP²-C（carbon）and Cu was investigated using first principle calculations.Various factors such as interface geometry,interface charge transfer,work function,Bader charge,charge differential density distribution,and electron state density were analyzed and studied to optimize the Cu/C（sp²）interface.The main findings and conclusions of this study are as follows:（1）Through the acidification process,a shell layer with C-O-Si covalent bonds,approximately 10 nm thick,was successfully formed on the surface of CNTs.The CNTs-fluid/Cu composite powder was prepared by blending CNTs-fluid and Cu powder using molecular blending technology,and the CNTs-fluid was uniformly dispersed in the Cu matrix when the content of CNTs-fluid was less than 0.75wt.%.（2）When the CNTs-fluid content was 0.75wt.%,the mechanical properties of rolled CNTs-fluid/Cu composite were the best,with a yield strength（YS）and ultimate tensile stress（UTS）of 343 MPa and 416 MPa,respectively.These values were 174%and 68%higher,respectively,than that of pure Cu under the same process.TEM analysis showed that a large number of CNTs-fluid were distributed at the grain boundaries of the Cu matrix,and oxygen-containing functional groups oxidized with Cu during the sintering process,resulting in the formation of Cu₂O at the interface.Thus,the mechanical properties of CNTs-fluid/Cu composites were greatly improved.（3）The conductivity of the CNTs-fluid/Cu material was close to that of the pure Cu sample under the same rolling state,with a conductivity of 97%of pure Cu.This similarity in conductivity to the CNTs fluid in enhancing the polymer is mainly due to the optimized surface defects grafted on the CNTs surface during the synthesis of CNTs-fluid.Additionally,well-dispersed CNTs weakened electron scattering.Furthermore,the thermal conductivity of the CNTs-fluid/Cu composite increased gradually with temperature,reaching 310 W/m·K at 500℃with a 0.75wt.%content,indicating good heat dissipation at higher temperatures.（4）CNTs-fluid/Cu₂O composite powder was prepared using the molecular blending method,which was then combined with Ti nanoparticles after reduction to create CNT-fluid/Cu-（Ti）composite material.The ultimate tensile strength of sintered composites with 1wt.%CNTs is 403 MPa,about 63%higher than that of sintered pure Cu（248 MPa）.The ultimate tensile strength of the rolled composite is 491 MPa,approximately 85%higher than that of rolled Cu（265 MPa）.The yield strength（YS）and ultimate tensile strength（UTS）of 0.5wt.%CNTs-fluid/Cu-（Ti）composite were332 MPa and 405 MPa,respectively,with a fracture elongation（EL）as high as 16.8%.The elongation of CNTs-fluid/Cu in the rolled state is about 273%higher than that without adding nano Ti.（5）The Cu/C（sp2）interface was calculated using first principles,with sp2-C represented by a graphene（GR）structure.A supercellular model was constructed and used to calculate the interface mismatch.Three different atomic structures were constructed and optimized for the interface model.The equilibrium average distance of Cu₂O forming the Cu/GR interface was found to decrease from 3.10（?）to 2.25（?）.Additionally,the interface binding energy increased to-2.623 J/m².These findings suggest that the interface binding strength of the composite material is improved,which in turn enhances its mechanical properties.The presence of a small amount of Cu₂O was found to contribute to the interface binding and electron transport of the composite material.The mechanism behind this interface enhancement and its effect on mechanical properties were revealed.The large difference in work function between Cu and the GR interface strongly affects the electrical conductivity of the composite material when the amount of Cu₂O and the mean free path of electrons reach a certain order of magnitude.To improve the electrical conductivity of the composite material,physical adsorption of GR and O is weak,as the transferred electrons tend to gather on O ions.However,the preparation of CNTs-fluid enhances the binding of C-O,thereby improving the ability of electron transfer at the interface and subsequently enhancing the electrical conductivity of the material.