| Copper matrix composite material has the characteristics of high strength,high conductivity and wear resistance,which has great application potential in electronics,machinery,electric power and other industries.Carbon nanotubes,with their superior mechanical,thermal and electrical properties,are cheaper than graphene,making them ideal reinforcers for copper-based composites.Poor wettability of carbon/copper interface and high surface energy of carbon nanotubes lead to poor sintering density,poor interfacial bonding and poor dispersion of carbon nanotubes reinforced copper matrix（CNTs/Cu）composites.In this paper,a combination of oscillating hot pressing sintering and CNT copper plating was used to explore the preparation of high density and high performance CNTs/Cu composites at low temperature.The mechanism of hot oscillation pressing sintering was studied and the preparation process was optimized.This paper uses carbon nanotubes and copper powder as raw materials.Firstly,to improve the interface binding of the substrate,the copper plated carbon nanotubes and the copper powder were mixed,and then the CNTs/Cu composite was prepared by oscillation and hot pressure sintering.Focus on the influence of copper plating time and copper salt concentration on the purity and uniformity,the influence of ball grinding parameters on CNT uniformity,the compaction mechanism of oscillation sintering and the process parameters of the microstructure and mechanical properties of copper composite effect law.The following conclusions are drawn:（1）A layer of uniform copper coating with less oxygen content is coated on the CNT surface through purification and acidification.The optimal copper plating and heat treatment process parameters are: copper sulfate concentration: 0.06 mol/L,chemical plating time: 60 min,heat treatment temperature and time are 350 ℃ and 1.5 h respectively.（2）By regulating the ball grinding process parameters and the carbon tube content,the uniform dispersion of carbon nanotubes in the copper matrix is realized.With the increase of CNT content,the density and hardness increase first and then decrease.When CNT content was 1vol.%,the density was 99.59% and hardness was 151.1 HV.Overall consideration,the best parameters: the ball grinding time is 3h,without any control agent;the CNT content is 1 vol.%.（3）Sintering kinetics studies show that the stress exponent is between 1 and 2 during hot oscillatory pressing sintering（HOP）when the density is less than 92%,indicating that the compaction mechanism swings between atomic diffusion and grain boundary slip. When the density is greater than 92%,the stress exponent is between 3 and 5,and the densification mechanism is mainly plastic deformation.Therefore,the larger stress exponent of HOP compared to HP,implies a higher contribution of plastic deformation to densification during HOP.This is consistent with the results of structural inspection that HOP sintering produces more small Angle grain boundaries and microscopic defects.Compared with hot pressing sintering（HP）,HOP can significantly improve the density and hardness due to the plastic deformation mechanism.As the oscillation pressure at low temperature causes more plastic deformation in the copper matrix,the change trend of hardness of HOP sample with sintering temperature is opposite to that of HP sample.（4）High-performance composites were prepared by regulating the oscillation process parameters.The experimental results show that with the increase of the oscillation frequency,the density,hardness and thermal conductivity show a trend of increasing first and then decreasing;With the increase of the oscillation pressure values,the density and hardness gradually increase（except 70 MPa）,and the thermal conductivity decreases;with the oscillation amplitude,the density gradually increases,and the thermal conductivity decreases.Overall,the best process parameters: oscillation frequency is 15Hz;median pressure is 60 MPa;and amplitude is 10 MPa. |
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