Preparation And Properties Of Synergistically Reinforced Copper Matrix Composites

Copper（Cu）is an essential material in our modern electrical and electronic information society.Copper matrix composites are expected to serve as an alternative to metallic copper in production and lives applications,aiming for better performance,sustainability and efficiency.In recent years,due to the excellent properties of carbon nanotubes,it is known as the best reinforcing phase for metal matrix composites,and scientific research reports on CNT-reinforced copper matrix composites are increasing.But the current research on CNT-reinforced copper matrix composites still suffers from the problems that CNT is difficult to disperse in the Cu matrix,the CNT-Cu interface bond is weak to bring out the excellent properties of CNT,and it is difficult to properly solve the conflicts between strength and toughness and strength and electrical conductivity of a single CNT-reinforced copper matrix composite.With these problems in mind,this paper designs a theoretical concept of synergistic strengthening to prepare a copper matrix composite with CNT and tungsten（W）particles by powder metallurgy combined with spray pyrolysis and a copper matrix composite with CNT and carbonized polymer dots（CPD）by powder metallurgy combined with electrostatic adsorption,and two lines of research were conducted to investigate the effects of CNT and the particles on the mechanical properties and electrical conductivity of copper matrix composites.The experimental results showed that:（1）CNT-W reinforcement prepared by spray pyrolysis with submicron W particles and interconnected structures,where the W particles on the CNT surface facilitate the weakening of the van der Waals effect between the CNTs and improve the dispersion of the CNT in the matrix by reducing the size and specific gravity difference between the CNT and the Cu particles.Transmission characterization of CNT-W/Cu composites revealed a clean and tight CNT/Cu interface,while the presence of Cu₂O was also found in the interfacial region,due to the spray pyrolysis process acting as a surface modification for CNT,with the introduced oxygen-containing functional groups providing oxygen atoms to react with the copper matrix to form Cu₂O,providing chemical bonding between the CNT and copper interfaces and improving the interfacial bonding.（2）The yield strengths and tensile strengths of the CPD-CNT/Cu composites were 195.36MPa and 305.95 MPa,respectively,an increase of 109.46%and 43.50%compared to pure copper,and an elongation of 29%,comparable to that of pure copper.The yield strengths and tensile strengths of the CPD/Cu composites were 99.60 MPa and 221.74 MPa,respectively;the yield strengths and tensile strengths of the CNT/Cu composites were 170.25 MPa and 269.29 MPa,respectively.The CPD/Cu composite achieved an electrical conductivity of 95.50%IACS,which is slightly higher than that of pure copper at 92.40%IACS,while the CPD-CNT/Cu composite achieved an electrical conductivity of 88.33%IACS,which is also higher than that of the CNT/Cu composite（85.06%IACS）,indicating that the addition of CPD significantly improves the electrical conductivity of the composite.The reinforcement of the composite is due to the synergistic effect of CPD and CNT and the total reinforcement is even better than the sum of CPD and CNT added alone.This is due to the good interfacial bonding between the acidified CNT and the Cu substrate,the high load transfer efficiency of the CNT,and the pegging effect of the CPD and CNT refining the grain size and impeding the movement of dislocations.The formation of annealed twins promotes dislocation entanglement and increases the strain hardening rate of the composite,resulting in a good strength-toughness combination for the CPD-CNT/Cu composite.The investigation of the strengthening and conductive mechanisms revealed that the incorporation of CPD and CNT reinforcements led to grain refinement,good interfacial bonding between CNT and copper matrix enhanced the load transfer strengthening efficiency of CNT,and dislocation strengthening during deformation,all three being simultaneously the main mechanisms affecting the tensile strength of the composite.In addition,the excellent electrical conductivity of the composites can be attributed to the unique electrical properties（ultra-high carrier mobility）of the CPD forming fast channels for electron transport at the Cu grain boundaries and the good interfacial bonding of the CNT to the Cu,reducing the resistance caused by grain boundary scattering and interfacial scattering.In addition,CPD is loaded on the surface of the carbon nanotubes and the synergistic effect of CPD and CNT takes full advantage of the ultra-high average free range of CNT to improve the electrical conductivity of the composites.