Study On Diamond/Copper Composite Coating Prepared By Mechanical Alloying

Pure copper possesses excellent thermal conductivity,electrical conductivity and corrosion resistance,while diamond-Cu composites have higher thermal conductivity and lower thermal expansion coefficient.Both of the above materials have broad application prospects in heat sink materials,but they also have their own shortcomings,such as high thermal expansion,poor abrasion resistance and low strength of pure copper,poor processing properties of diamond/copper composites.Therefore,this experiment is based on mechanical alloying coating technology to prepare diamond/copper composite coating on pure copper surface,aiming to maintain the thermal conductivity and processing performance of pure copper substrate,while reducing surface thermal expansion and improving wear resistance.This experiment is mainly divided into two parts.The first part mainly studies the influence of the particle size and content of diamond in the raw powder on the microstructure and properties of the composite coating.Combined with the variation of powder,coating and substrate,the deposition mechanism of diamond/copper composite coating is summarized.Studies have shown that the diamond particles in the coating are severely shattered but not graphitized,the particle size is mainly distributed in the range of 500 nm to 2?m,and there are a few coarse diamond particles in the coating-substrate interface and in the inner layer.Grain refinement and lattice distortion of copper occur in the coating.The particle size of the diamond in the raw powder mainly affects the size and distribution of the coarse diamond in the coating,while the diamond content affects the thickness and bonding force of the coating.During thermal shock,the inlaid structure interface,partial debonding of inner diamonds and good internal bonding make the coating effective against thermal shock.During the deposition process of the coating,the surface reactivity of the pure copper substrate is increased,the diamond particles are continuously refined.The cold welding ability of the composite powder is first increased and then decreased,and the thickness of the coating is first increased and then stabilized.Continuous external compressive stress and short-range diffusion of copper atoms are the key to coating densification.The microstructure and properties of the coating were compared to obtain the optimum process parameters:the raw powder has a diamond particle size of 140 mesh,a content of 30 wt.%,and a ball milling time of 7 h.The second part is the optimization study of the microstructure and properties of the coating,which is divided into direct annealing and Cr-doped+annealing.Unannealed coatings provide excellent wear resistance and poor thermal conductivity.After recrystallization annealing,the grain size increases,the microscopic defects decrease,the coating softens,so the microhardness and the wear resistance decrease,and the heat conduction performance is improved.After annealing at 500?,the microhardness and wear resistance of the coatings slightly decreased,and the thermal conductivity is better than that of T2pure copper annealed at the same temperature.After the high temperature annealing of 1 wt.%Cr and subsequent 700?,the Cr atoms in the coating diffuse to the diamond surface and form carbides,which improves the diamond/copper interface bonding force.The microhardness and wear resistance of the coating decreased less than the 700?annealed coating without Cr.The thermal conductivity is increased to 346.93 W·m^-1·K^-1,which is the optimal performance in this paper.Continue to increase the annealing temperature,the copper atoms in the coating diffuse to form a strip-like zone,including copper-rich phases and carbon-rich phases.The microstructure became loose,and the microhardness,wear resistance and thermal conductivity decreased to varying degrees.The optimum annealing process in this experiment is that annealing at 700?after adding 1wt.%Cr.