Research On Preparation And Tribological Properties Of Copper Matrix With Graphite Self-lubricating Materials

Copper(Cu)-graphite(Gr) composite was prepared by the powder metallurgical method with the Gr coated by Cu, or nickel (Ni). The interfacial combination of Gr and Cu-matrix were systematically studied. The mechanical properties of the composites were tested and analyzed. The wear behaviors and the wear mechanisms of the composites were also investigated, which can provide the theoretical fundamental and technical supports for the development of new type high performance Cu-Gr self-lubricating(SL) composites.The Gr particles were coated with a thin, uniform and compact layer of Ni or Cu by electroless plating, and then Cu-Gr SL materials were prepared by the repressing and resintering technique. The influence of Cu or Ni-coated Gr and the coating spheroidization on the interfacial combination of Gr and Cu-matrix were investigated. The proper sintering temperature can make the best use of the good effect of the Cu or Ni coatings on interfacial combination of Gr and Cu-matrix. The interfaces between Gr and Cu matrix were tightly connected and the gaps or cracks were not observed in the interfaces, which resulted in the increase of strength and toughness of the composites. Furthermore, repressing and resintering technique is also beneficial to making use of the advantage of the surface treatment of the Gr particles. And the results showed that the Ni coating is superior to the Cu coating.After the friction and wear tests under the different conditions, the worn surfaces and the cross sections, compositions and morphologies of deris were analyzed by micro-analysis method. And the wear behaviors and mechanisms of Cu-Gr composites were systematically investigated. Under our test conditions, the Gr lubricating films of Cu-Gr composites with the Gr coated by Cu or Ni have better adhesion performance with Cu-matrix, whose lubricating and anti-friction properties are superior to those of composites made by pure Gr. Especially, the lubricating and anti-friction properties of composites with Ni-coated Gr is better. Wear process of the composites has three typical stages, i.e., slight wear stage, medium wear stage and severe wear stage. At the slight wear stage, the dynamic process of cracking, peeling off and repairing of the SL film was in dynamical equilibrium. At the medium wear stage, the dynamical equilibrium is broken, and the main wear mechanisms of the composites were abrasion and adhesion. At the severe wear stage, there is no continuous SL film on the friction surfaces, most interfaces between the wear couples directly contact each other, and the heavy plastic deformation occurred in the subsurface area, where the nucleation of cracks took place at the Gr particles. The subsequent propagation of the cracks leaded to the worn particles peeled off from the surface. The main wear mechanism was adhesion, accompanied with oxidation wear. The results showed that the coating on Gr is a key technique to improve the tribological properties of the Cu-Gr SL composites. Study on the Cu matrix SL composites prepared by using Ni-coated Gr and their wear behavior has been not reported before, so this is one of the innovations of this thesis. It is of great significances in theory and practice for developing the new type of Cu-Gr SL composites and enriching the tribological research.