Electrodeposition Method To Prepare CNTs/Cu Composite Powder And Its Composite Material Properties

Copper matrix materials with high strength and high electrical properties have become the focus of researchers.Carbon nanotubes(CNTs)are regarded as an ideal reinforcement of Cu matrix composites due to their unique atomic structure,superior mechanical and electrical properties.CNTs/Cu composites have great application potential in some fields,such as electrical contact materials and electronic packages.However,poor dispersion of CNTs and poor interfacial bonding between CNTs and Cu matrix are always formed due to the large aspect ratio of CNTs and poor wettability between them.Furthermore,it is often difficult to simultaneously achieve high strength and high electrical properties of Cu matrix materials,a dramatic loss of conductivity is frequently accompanied with the enhancement of mechanical strength.The uniform dispersion of CNTs,CNTs/Cu interface and organizational structure of composites are the key aspects to achieving high strength and high conductivity of CNTs/Cu composites.In order to solve above problems,it is necessary to develop a novel technique for fabricating CNTs/Cu composites.Multiwalled CNTs were used as raw material in the dissertation.Firstly,CNTs dispersion was obtained by a dispersing process with a combination of some methods,then CNTs/Cu composite powders were prepared by electrodeposition.Finally,CNTs/Cu composites were consolidated by vacuum hot pressing followed by cold rolling.The main work and results of this study are as follows:(1)A dispersing CNTs process was proposed.The process including acid treatment,dispersant-assisted ultrasonic homogenization and centrifugation was used to improve the dispersity of CNTs,the stable CNTs dispersion was successfully obtained.Functional groups formed on the surface of CNTs by acid treatment and the use of dispersant WDIS significantly improve the dispersion of CNTs as well as dispersion stability of CNTs in the electrolyte.(2)The effects of CNTs size and different types of dispersants on properties of CNTs/Cu powders and composites were revealed.The comparison of dispersity of different types of CNTs in the solution through above-mentioned dispersing process was conducted.The effects of different types of dispersants on the growth behavior and micromorphologies of CNTs/Cu composite powders during electrodeposition were studied.The optimum dispersant and CNTs with suitable diameter and length were selected.Good comprehensive properties of CNTs/Cu composites were obtained using short CNTs with diameter of 20-30 nm and length of 0.5-2?m.Besides,CNTs content and dispersity in composite powders were best when choosing WDIS as the dispersant.(3)The process parameters of electrodeposition for fabricating CNTs/Cu composite powders were optimized.CNTs/Cu composites exhibit good comprehensive properties(strength of 417.11 MPa?conductivity of 90.16%IACS)obtained at current density of200 mA/cm~2,Cu ions concentration of 10 g/L under ultrasonication.It is found that scraping powders treatment during electrodeposition not only makes CNTs uniformly disperse in the matrix,realizes good CNTs/Cu interface,but also obviously reduces particle size of composite powders from 52.75 to 34.78?m with uniform size distribution.Hence scraping powders treatment significantly enhances the performance of composites.(4)The process parameters of vacuum hot pressing and cold rolling for fabricating CNTs/Cu composites were also optimized.CNTs/Cu composite powders have good thermoplasticity,resulting in sintering temperature and sintering duration time being as low as 500?,30 min,respectively.What is more,lots of twins are formed in Cu matrix during sintering process.Increasing sintering pressure to 80 MPa and rolling deformation to 80%can achieve close interface between CNTs and Cu.1.65 vol%CNTs/Cu composites show high strength of 505.63 MPa,good ductility of about 8%,simultaneously maintain high conductivity of over 90%IACS.(5)Through the analysis of the microstructure,fracture morphology and interface of the composites,it is revealed that load transfer efficiency is the primary strengthening mechanism,and multiple strengthening mechanisms lead to the improvement of mechanical property of the composites.CNTs are mainly located in the interior of grains and twins as well as at twin boundaries,which are beneficial to load transfer and dislocation strengthening of CNTs,thus,the excellent mechanical properties of CNTs can be effectively realized.In addition,CNTs network further enhances load transfer efficiency and blockage of dislocation motion,besides,provides new pathways for electron transport.What is more,the formation of twins plays an important role in achieving high electrical conductivity of composites.In a word,CNTs/Cu composites with high strength and high electrical conductivity are obtained by improving dispersion of CNTs in the electrolyte as well as interfacial bonding between CNTs and Cu matrix.Besides,a process technique by combining electrodeposition and powder metallurgy is obtained to fabricate CNTs/Cu composites.