Study On Microstructure And Tribological Properties Of Laminated Flake Graphite/Copper Matrix Composites

Due to the special crystal structure of flake graphite,when subjected to shear forces,the flake graphite will break the van der Waals forces between the different flake layers and produce slip,so the flake graphite has good lubricating properties and is widely used in the study of the tribological properties of copper matrix composites.However,the soft structure of flake graphite is easily damaged and the wettability between flake graphite and copper matrix is poor,resulting in poor interfacial bonding between flake graphite and copper matrix.Therefore,it is necessary to improve the strength of flake graphite and the interfacial bonding between flake graphite and copper matrix for the preparation of flake graphite/copper matrix composites with excellent properties.To this end,a layered graphite with uniform flake spacing while retaining the structure of flake graphite was prepared by chemical oxidation.The layered graphite has a larger specific surface area than the flake graphite.The surface of the flake graphite and the layered flake graphite is coated with a homogeneous copper and nickel layer by chemical plating,which increases the strength of the graphite and improves the wettability with the copper substrate.The powders were mixed with electrolytic copper powder by ball milling and sintered by rapid hot press sintering.The following conclusions were obtained:(1)A layered graphite that retains the structure of flake graphite while having uniform flake spacing was successfully prepared by chemical oxidation.The influencing factors of the layered structure of flake graphite were also investigated.It was shown that the lamellar spacing of the layered graphite increased gradually with the increase of the mass of the oxidant at a certain concentration of the intercalant and water bath temperature;the lamellar spacing of the layered graphite increased with the increase of the concentration of the intercalant at a certain mass of the oxidant and water bath temperature;the lamellar spacing of the layered graphite increased with the increase of the water bath temperature at a certain mass of the oxidant and the concentration of the intercalant;the lamellar spacing of the layered graphite increased with the increase of the water bath temperature.increases with increasing water and temperature.(2)The metallic copper and metallic nickel were deposited on the surface of the flake graphite and the lamellae between the layered flake graphite by chemical plating,thus effectively improving the bonding ability between the flake graphite and the substrate.(3)Preparation of flake graphite/copper matrix composites with a mass fraction of 6%,copper-plated flake graphite/copper matrix composites and copper-plated layered graphite/copper matrix composites respectively by rapid hot-press sintering,and it was found that chemically plating copper on the surface of flake graphite resulted in an increase in the hardness and density of the copper matrix.(4)Samples incorporating copper plated layered flake graphite had the highest coefficient of friction and the lowest wear rate.This is because the graphite is less likely to break and fall off during the friction process,and the metallic copper layer in the flake graphite layer increases the strength and hardness of the flake graphite itself.The samples with copper layered graphite have a higher coefficient of friction and wear resistance than those with nickel layered graphite when added in a certain amount.This is because after friction testing,the bond between the copper layered graphite and the copper substrate is better than the bond between the nickel layered graphite and the copper substrate.