Preparation And Study On The Properties Of Copper-based Composite Reinforced With Carbon Nanotubes

Carbon Nanotubes(CNTs)are considered as one of the best fillers to reinforce composites due to their excellent mechanical properties,unique electrical and thermal conductivities as well as their extremely low thermal expansion coefficient.As the result,CNT reinforced composites have been gradually become a very important research topic,especially for Cu-based carbon nanotube composites due to the promising resultant material properties and the potential of broad applications.However,CNTs have extremely large aspect ratio and large specific surface area,and CNTs aggregation is very common due to the Van Der Waal force.The “wetting” between carbon and copper is poor and there is no chemical reaction to take place between them.Therefore,the main challenges in copper-CNT composite are the uniformity in dispersion of carbon nanotubes and the interfacial bonding between CNTs and the copper matrix.Nickel and copper can form a completely soluble alloy system,and nickel and carbon have good intermediate bonding.Therefore,nickel plating on the surface of carbon nanotubes can effectively improve the dispersion of carbon nanotubes as well as the interfacial bonding strength between Cu and Ni/CNTs in composites.In this paper,the fabrication of nickel-coated carbon nanotubes(CNTs/Ni)were investigated by the chemical nickel plating process and the fabricated Ni-coated CNTs were used to fabricate Cu-Ni/CNTs composites by a rapid vacuum hot-pressing sintering process.The main research contents and the obtained results are provided in the following.Nickel plating on carbon nanotubes was carried out by both a palladium chloride method and a potassium borohydride method respectively.Under the SEM observation,it’s shown that the nickel coating on CNTs prepared by the palladium chloride method was more uniform and better in coverage.XRD analysis also showed that Ni grains obtained by the palladium chloride method were much smaller.Raman Spectroscopy test showed that the signal of CNTs/Ni prepared by palladium chloride method was relatively weaker,indicating that the nickel metal covered on the surface of CNTs wasmore uniform.However,the cost of palladium chloride is more expensive than potassium borohydride.The phase transition temperature of the copper powders was characterized by differential scanning calorimeter(DSC),to determine the powder metallurgy sintering temperature and 900 ℃ was chosen as the sintering temperature for the powder metallurgy process;It has also studied the pressure effects on the obtained composite that different pressure values of 45 MPa,55MPa,65 MPa and 75 MPa were invested on the resultant density and the resultant hardness of fabricated copper/CNT composites.The pressure value of 65 MPa was selected in this experiment.The work also studied the CNT adding effects that composites consisting of 0.5wt%,1wt%,1.5wt%,2wt% and3wt% were investigated.Bothe metallographic microscope and SEM were used for characterization purposes.Results have shown that as the content of CNTs increased,the strength and hardness increased.When the content of carbon nanotubes was about 1%,the tensile strength of Cu-Ni/CNTs composites reached to 418 MPa,or about 50.9% increase.The hardness was increased about 10%.The electrical conductivity of Cu-Ni/CNTs composites was tested with both a digital source meter and a data acquisition system.The best electrical conductivity also occurred at carbon nanotube content of 1%.However,the results on thermal conductivity was not good as expected,which needs to be investigated further.Through analysis and comparison,the strengthening effect of CNTs/Ni on composite materials is significantly better than that of pure CNTs added.