The Effect Of Reinforcement Modification On The Microstructure And Mechanical Properties Of Carbon Nanotube-reinforced Copper Matrix Composites

Carbon nanotubes(CNTs),with the unique structure and excellent properties,are suggested as one of the ideal composites reinforcements.CNTs reinforced copper-based composites can considerably enhance the strength.However,it is often accompanied by a decrease in plasticity and electrical conductivity,and the comprehensive performance advantage between the reinforcement and the metal matrix can not be fully exerted.The design of the composite structure is used to realize the regulation and optimization of the distribution form of the reinforced body,which is an important idea to realize the joint strengthening of different properties of the CNTs composite material.In this paper,CNT / Cu composites were prepared by three different methods.The effects of reinforcement structure,reinforcement surface modification and interface microstructure on the mechanical properties of the composites were studied.(1)The structure of CNTs was regulated by hydrogen etching.Firstly,the CNTs was acidified.Secondly,the pure copper powder was ground into flakes,and the acidified CNTs and flake copper powder were milled to obtain composite powders,Then the composite powder was put into the tubular furnace and hydrogen was introduced to obtain the CNTs and copper powder after hydrogen etching.Finally,the composite powder was prepared into bulk materials by spark plasma sintering(SPS).The results show that the cnt-gp with both CNTs and GP characteristics can be obtained by hydrogen etching under the catalysis of copper,GP structure can effectively increase the contact area between the reinforcement and the metal matrix,improve the load transfer efficiency,and thus improve the strength of the composite;while CNTs structure has a large aspect ratio,which can effectively improve the tensile plasticity of the composite.The tensile strength and elongation at break of CNT / Cu composite without hydrogen etching were 243 mpa and 6.0%,respectively.The mechanical properties of CNT-GP / Cu composites etched by hydrogen are much better than those of CNT / Cu composites without hydrogen.The tensile strength andelongation of CNT-GP / Cu composites with hydrogen etching time of 30 minutes and60 minutes are 285 MPa and 14.0% respectively,and those with hydrogen etching time of 60 minutes are 303 MPa and 9.8% respectively.(2)The surface of the CNTs is Ti C plated by a pressureless sintering process.First,the CNTs and titanium powder are weighed for mixed ball milling,and then the CNTs and the mixed ball mill are added.Secondly,the composite powder obtained by ball milling was subjected to pressureless SPS sintering to obtain Ti C modified CNTs reinforcement.Then,the reinforcement and copper powder are mixed and ball milled,and finally the obtained composite powder is prepared into a bulk material by SPS sintering.The experimental results show that using pressureless SPS sintering process,a layer of Ti C can be deposited on the surface of CNTs,The Ti C@CNTs reinforcement is beneficial to the uniform dispersion of CNTs in the Cu matrix,thereby increasing the total load that the Ti C@CNT/Cu composite can withstand and increasing the strength of the composite.The tensile strength of Ti C@CNT/Cu composite reached 270 MPa,which was significantly higher than that of CNT/Cu composite(242 MPa)and pure copper(233 MPa).(3)Ti C was in situ formed on CNTs by molecular blending and hot pressing sintering.Firstly,CNTs / Cu composite powder was prepared by molecular blending method.Secondly,a proper amount of titanium powder was weighed and mixed with CNT / Cu composite powder for ball milling.After reduction,composite powder was obtained.As the same,the copper powder and titanium powder were first weighed and milled together,then CNTs were added for milled together,and the composite powder was obtained after reduction.At last,the composite powder was prepared into block composite material and alloy material by hot pressing sintering process.The experimental results show that tic is formed in the composites prepared by the two processes,but the distribution of tic is more uniform in the composites prepared by molecular blending,This is because molecular blending can reduce the aggregation of CNTs,which is conducive to the uniform dispersion of CNTs in Cu matrix.The strength of the composite prepared by molecular blending method is 366 MPa,whichis significantly higher than that of the composite prepared by high energy ball milling method.