Preparation Of Laminated Carbon Nanotubes Reinforced Copper Composites And The Strengthening And Toughening Mechanism

Carbon nanotubes（CNTs）reinforced Cu composites with laminated structure were constructed,and the microstructure and mechanical properties was detected to analyze the strengthening and toughening mechanism in this work.Electrophoretic deposition（EPD）was adopted to uniformly deposite Carbon nanotubes（CNTs）on Cu foils,and followed by hot pressing and rolling,CNTs reinforced Cu laminated composites with different structural parameters were fabricated.SEM,TEM,EBSD and XRD were adopted in the evolution of mechanical properties and microstructure of pure Cu and the composites.In-situ tensile combined with Digital Image Correlation（DIC）were also conducted on pure Cu and the composites to track the evolution of strain distribution during tensile process.The structural variation caused by the introduction of laminated structure was studied and the strengthening and toughening mechanism were uncovered.Fabricating process to deposite CNTs on Cu foils through EPD was studied.Raw CNTs are always agglomerated in clusters,the surface treatment of CNTs to introduce oxygen-containing functional group is thus a key step for EPD.EPD of CNTs by the electric charges introduced by the acid treatment was not enough to support the movement of CNTs.The amount of CNTs on the surface of Cu foils as anode were not change obiviously along with the increase of time.By adding Al（NO₃）₃ particles in the mixture of ethanol and acetone（Volume ratio 1:1）,the amount of CNTs on Cu foils as cathode were increased with the increasing time of EPD.However,poor and rich regions of CNTs were observed.Further increasing the amount of Al（NO₃）₃ particles,uniform dispersion of CNTs were detected with different deposition time.Lowering the voltage or shortening the deposition time,the amount of CNTs that deposited on Cu foils was decreased.The ideal amount of CNTs and Al（NO₃）₃ particles is 0.017 and 0.033mg/ml,and the voltage is 30V.When singly adopted isopropanol as electrophoretic solution,uniform CNTs dispersion can also be formed on Cu foils.Because of the larger viscosity for isopropanol,the time needed to deposite CNTs was also prolonged.The structure of CNTs on Cu foils can be changed by adjusting the parameters in EPD.The optimal process to construct the structural units is the key to fabricate the laminated composites.Hot pressing can facilicate the incorporation of structural units to fabricate the laminated composites.For the composites fabricated with 50μm thickness Cu foils that were deposited CNTs for different time,the tensile test results illustrated that the yield strength（YS）of the composites were increased with the increased amount of CNTs while elongation decreased.The fracture behavior of laminated composites was transferred to the fracture of the adjacent Cu foils from the ductile fracture of pure Cu.Selecting the EPD time of 60s to analyse the effect of rolling process on the adhesion of the adjacent Cu foils and the microstructure of the Cu layers.Mataining the total rolling reduction as 60%,the thickness of Cu layers was about20μm.The composite exhibited simonetaneously enhanced strength and ductility.Increasing the rolling reduction of the first pass to 40%and shortening the annealing time after each rolling pass to 5min,the composite enhibited further enhanced yield strength while no sacrifice of ductility.However,further increasing the total rolling reduction,pure Cu and the composite showed almost same mechanical properties.Changing the thickness of Cu foils to 30 and 100μm and maintaining the EPD time as 60s to buils structural units,after hot pressing and rolling,the thickness of Cu layers in the composites decreased to 10 and 37μm.The composite showed simonetaneously enhanced strength and ductility with 10μm Cu layers.However,the ductility decreased while the strength increased for composites with Cu layers thickness of 37μm.Structural parameters thus playing important role on the toughness of composites.Combining the tensile test results and the calculation results,dislocation strengthening is the main strengthening part.In-situ tensile test combined DIC was adopted to observe the strain distribution.When the thickness of Cu layers is 37μm,the concentration of deformation was detected in the composite and thus exhibiting decreased elongation.Observation of the composite with 20%tensile strain on RD-ND plane enhibited obviously deformed and undeformed areas,the misorientation of the adjacent grains induced stress concentration and initiation of cracks at these places.With thinner Cu layers,the strain distribution during tensile test was more homogeneous,and strain localization was restrained and the postponed the necking.The interfaces also prolonged the crack pathway.Neutron diffraction was adopted on pure Cu and composites with original 50μm foils to analyze the mode of plastic deformation.The lattice strain of{111}Cu in pure Cu exhibited sudden decrease,which demonstrated twin deformation mechanism.Differently,the lattice strain of{111}Cu in laminated composite exhibited gradualy increased value,which demonstrated slip deformation mechanism.