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

Self-lubricating (SL) materials exhibit superior performances especially in many cases with a little oil or without oil. Copper (Cu) matrix and graphite (Gr) SL composite, as one of the most important metal matrix SL composites, is widely used owing to its excellent tribological properties, oxidization resistance and corrosion resistance etc. However, Cu and Gr do not dissolve and react each other. In Cu-Gr composite, the combination of Cu and Gr is a false alloy, there are many pores in the material, which greatly limit the strength, lubricating performance and service temperature of the composite. In order to meet the needs of special SL materials served in severe conditions, it is very necessary to research and develop the high performance Cu-Gr SL composites. Therefore, it is of important signification to study the wear behavior and mechanism of Cu-Gr SL composites in different service conditions systematically and to analyze the wear and anti-friction process of the composites theoretically, which can provide a theoretical fundamental and technical supports for the development of new type high performance Cu-Gr SL composites.In this thesis, the tin bronze was selected as the matrix, which was reinforced by adding alloy elements, such as nickel (Ni), iron (Fe) etc., and Gr particles with appropriate size and quantity was added as the solid self-lubricant. The Gr particles were plated with a layer of Ni, Cu by electroless deposition. The effect of the coatings on the combination of the interfaces was studied. The results showed that the combination of the interfaces between matrix and coated Gr was affected by the high temperature sintering process, and the the interface combination was improved by the coatings at a proper sintering temperature, the Gr and Cu alloy matrix were combined well, 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 also showed that the Ni coating is superior to the Cu coating.After the wear and friction tests, the microstructures, fracture morphologies, worn surfaces, composition and morphology of debris of the composite samples were analyzed by OM (optical microscope), SEM (scanning electron microscope), XRD (X-ray diffraction), EDS (energy dispersion spectrometer) and Ferrography, respectively. The wear behaviors and mechanisms were investigated in detail in the temperature range of room temperature to 500℃. During the wear tests, Gr particles were pressed and moved to surface, and then gradually deformed into continuous thin solid lubricating film. After coated with Cu, Ni, the so-formed film was tightly adhered on the friction surfaces and caused good anti-friction. The composites showed low coefficient of friction and low rate. Under our test conditions, the wear process of the composite with 6% Gr has three typical stages, i.e., slight wear stage, medium wear stage and severe wear stage; whereas the wear process of the composite with coated Gr (coated with Cu, Ni) has only two typical stages, i.e., slight wear stage and severe wear stage. Under a certain load, the wear of the Cu-Gr SL composites increased and anti-friction became worse with the increase of the test temperature. The results showed that, at the slight wear stage, the dynamic process of cracking,...