SPS Preparation Of CNT/Cu Composite Material And Its Mechanical And Electrical Properties

Carbon nanotubes reinforced copper matrix(CNT/Cu)composites have attracted much attention due to the excellent mechanical,electrical and thermal properties of CNTs.However,owing to these problems,(1)poor wetting behavior or weak interfacial bonding between CNTs and Cu;(2)high surface energy,high aspect ratio and strong Van der Waals forces,it is difficult to make evenly distribution of CNTs;(3)defect of CNTs,containing flaws in the tube wall,impurities,bends and kinks significantly decrease the conductivity of CNTs,even at low defect concentrations The existing research results show the mechanical and electrical properties of CNT/Cu were lower than its theoretical expectation.Therefore,it is a key issue to enhance mechanical and electrical properties of CNT/Cu composites.The thesis utilized the advantages of SPS,such as obtaining fine microstructure and modifying interface bonding,to study the microstructures and performances of composites via acid-treated CNTs and preparation technology.Then,the influence of CNTs modified by polydopamine(PDA)on microstructure and performances were investigated as well At last,the strengthening mechanism and electrical mechanism were studied.Overall,the main results as following;(1)A novel mixing method that combines wet mixing and conventional ball milling followed by SPS was used to fabricate CNT/Cu composites.In the CNT/Cu composites,the CNTs were uniformly dispersed whilst maintaining their integrity Consequently,a combination of high strength,ductility,and electrical conductivity was achieved by a CNT(2.5vol%)/Cu composites(ultimate tensile strength 280 MPa,elongation 41.7%,and electrical conductivity 53.1 MS/m)(2)With electrostatic repulsion of acid-treated CNTs overcome the van der Waals interaction force of CNTs,the different dispersion state of CNTs on CNT(2.5vol.%)/Cu powders were fabricated by wet mixing with different acid-treated time CNTs.The dispersion state of CNTs was enhanced with increasing acid-treated time.While,it was found that composite with homogeneous dispersion CNTs had the lowest electrical conductivity(52.47±1.97 MS/m)and that one with aggregation CNTs has the best conductivity(54.2±0.986 MS/m).Thus,it can be concluded that the dispersion of CNTs have negative influence on high electrical conductivity of CNT/Cu composites(3)The CNT@PDA(1.25vol.%)/Cu composites were fabricated by SPS with short sintering time and the influence of sintering temperature on interfacial layer PDA,microstructures and properties of composites were studied.Comparing with CNT/Cu composites,CNT@PDA/Cu composites(sintering temperature is 450℃)shows highest ultimate tensile strength(18%,275.6±7.7 MPa),yield strength(29.1%,271.3±2.6 MPa)and elongation(146%,9.6±3.2%).With increasing sintering temperature,ultimate tensile strength and yield strength were gradually decreased.In tha range of sintering temperature from 450 to 550℃,elongation increased with increasing temperature.However,the ultimate tensile strength,yield strength and elongation of CNT@PDA/Cu composites were obviously decreased when sintering temperature above 600℃.Furthermore,the drop of these performances inceasing with inceasing sintering temperature.Thus it can be seen low sintering temperature are beneficial to maintain PDA structure integrity,and achieve better interface bonding with Cu matrix.On the other hand,with increasing sintering temperature,PDA was changed to amorphous carbon,which remarkably deteriorate the mechanical and electrical properties of CNT/Cu composites(4)With further discussing the strengthening mechanism of wet mixing-conventional ball milling composites,it can be concluded that the Orowan strengthening mechanism,thermal-mismatch strengthening mechanism,and the load-transfer mechanism were the primary reason for improving mechanical strength of CNT/Cu composites.The theoretical reuslt was agree with experimental result,which demonstrate the evenly dispersion of CNTs effectively hinder the movement of dislocation and the load transfer was observed between CNTs and Cu matrix.Therefore,sample show excellent strength and elongation(5)A formula with the rule of mixtures(ROM)and all possible physical mechanisms were used to predict electrical conductivity of CNT/Cu composite(σc=σCNTsVCNTs+(1-VCNTs)/ρpc+ρdis+ρint).with using this formula,it can be achieved the following results:(1)the overall electrical conductivity of CNT/Cu composites was not effected by the values of electrical conductivity of CNTs,values of conductivity of matrix were the dominant factor;(2)increasing the probability of elastic scattering at the interface(p)was an effective method for improving electrical conductivity of CNT/Cu composites.These conclusion provide a reference for follow-up work.