Study On The Preparation And Tribological Properties Of Ultrafine-grained Copper And Its Composite Materials

Ultra-fine-grained copper exhibits excellent mechanical properties due to its small grain size.However,the changes in the morphology and number of grain boundaries may reduce the hardness and tribological properties of ultrafine-grained copper-based materials,so it is of great practical significance to study its thermal stability.Graphene is a highly lubricating material,which provides a new idea for improving the tribological properties of ultrafine-grained copper-based composites.This paper explores the process of electrolytic deposition of ultra-fine crystal copper,and discusses the influence of ultra-fine crystal copper with heat treatment under the optimal process.By adding graphene,the wear resistance of the material is improved.This article first uses pulse electrodeposition to prepare ultra-fine crystal copper.The effects of process parameters such as the content of ethylenediamine in the electrolyte,current density,and deposition time on the electrolytic deposition of ultra-fine crystal copper were studied.The results show that with the increase of ethylenediamine concentration,the grain size of ultrafine crystal copper first decreases and then increases,and the microhardness first increases and then decreases sharply when the current density is 5 A/dm² and the electrodeposition time is 10 h.When the concentration of ethylenediamine is 90 mL/L and the current density is 5 A/dm²,the grain size is the smallest and the hardness is the highest.At this time,the grain size can reach 30 nm,and the surface microhardness of ultra-fine crystal copper is as high as304HV0.1.As the current density increases,the microhardness of ultra-fine crystal copper first rises and then drops sharply.As the electrodeposition time increases to 10h,the thickness of the deposited layer gradually increases to 413?m,and the deposition rate gradually decreases.The samples prepared by the above process were annealed to explore the changes in their structure and properties at different annealing temperatures and annealing times.Both the annealing temperature and the annealing time have a significant effect on the grain orientation and grain size.When the annealing time is 20 min,the higher the annealing temperature,the larger the crystal grains.When the temperature is 400?,the crystal grains grow up obviously,and the size reaches about 2?m.When the annealing temperature is 400?,after 5 minutes,the hardness of the coating has dropped significantly.The regression equation of 400?isothermal annealing grain size and annealing time is:ln(D-D₀)=0.31lnt+5.58,the growth index of ultra-fine crystal copper is 0.31.when the annealing time is the same(20 min),the regression equation of grain size and annealing temperature is:ln(D-D₀)=-3.18T+12.6,its grain growth activation energy is 26 kJ/mol.Under the conditions of ethylenediamine content of 90 mL/L and current density of 5 A/dm²,the friction coefficient of the ultrafine crystal copper sample obtained by electrodeposition is 0.51,and the volume wear rate is 2.45×10^-5 mm³/(N·mm).After annealing at 400?,the friction coefficient was reduced to 0.41,and the volume wear rate increased by 51%;after adding 0.04 g/L graphene to the electrolyte,a graphene/copper composite coating was obtained by electrodeposition on the surface of the substrate.The friction coefficient is reduced to 0.16,and the volume wear rate is reduced by 23.4%;the graphene concentration is increased to 0.08 g/L,the friction coefficient of the sample is further reduced to 0.14,and the volume wear rate is reduced by 46.9%.Therefore,compared with microcrystalline pure copper,nanocrystalline pure copper exhibits better wear resistance,and the addition of graphene can further improve the wear resistance,and the effect is more significant when the concentration is higher.