| Cu base composites are considered to have great potential in application as a novel kind of advanced material due to combinations of high strength, conductivity, thermal conductivity similar to pure Cu, and good erosion resistance to electricity arc as well as excellent wear resistance. One of the most important application is the Cu base self-lubrication composite fabricated by adding solid lubricant into Cu alloy matrix. According to the statistics, 70% annual outputs of copper powders are used to produce friction materials through the world. C/Cu composite specially is always the priority for the electric contacts and brush materials, but the interface between the C and the Cu matrix exists in the form of mechanical bonding, this kind of low bonding strength often leads to the enforcement pulling out and falling out. Therefore, the improvement of strength, hardness and wear resistance has been the central task for the research and development of Cu base materials. The aim of the present study is to develop a Cu base self-lubriccating material with good friction and wear characteristics. On the basis of composition and processing parameter optimization, a kind of Cu base composite with nano structure strengthening surface and a kind of C/Cu composite have been successfully developed with good properties meeting the above demand using techniques including mechanical alloying, cold pressing and spark plasma sintering. All of these works lay a solid foundation for development of novel low-friction and anti-scuff Cu-based composite. The works include the following aspects: 1. Cu-based composite with surface nano structure has been successfully fabricated using cold pressing and SPS techniques, respectively. The surface layer of nano structure is 100-200μm thick, and the surface densification and microhardness are increased with increasing pressure. However, delamination occurred when surface nano structure layer was over thick; whereas no this phenomena happened to the composite by SPS, even though a transition zone of about 5 μm existed between the nano structure surface layer and the substrate, with fine grain size uniformly distributed both in the nano structure surface and the substrate and good bonding between the particles as well as between the nano structure surface layer and the substrate. 2. The effects of sintering parameters on the grain size were investigated. The results show that the applied current can activate the grain surface, so it has to be considered that the activation energy difference could affect the grain growth. As the sintering rate was low, grain size was mainly controlled by sintering time, and decreased with increasing sintering rate. Contrary to this, the grain size was greatly controlled by activation energy, increased with increasing sintering rate. 3. MA has been used to successfully produce the C/Cu composite powder. During MA, it is difficult to from nano crystalline structure from pure copper with fcc structure, the addition of graphite can change the morphology of the powder after MA. The copper exists in the form of nano/ submicro composite particles and pure nano particles. The carbon was present as nano layered structure and the amorphous. And finally these two elements were transformed into a mixture of composite particles with nano scaled subgrain, pure nano particles and amorphous composite powder. 4. The mechanism of solubility extension of carbon in the copper was discussed. The analysis reveals that the positive and low mixing enthalpy (ΔH=35.1KJ/mol) determines the diffusion reaction mechanism during MA, supersaturated solid solution of carbon in copper can be achieved instead of intermetallic. The lattice parameter fro the supersaturated solid solution increased with increasing milling time and graphite content of the composite powder, and went through a maximum value at 24 h, then decreased lightly. The grain size decreased with increasing milling time and graphite content. 5. The microstructures and properties of compacts C/Cu alloy fabricated using cold pressing and SPS were studied. It is noted that the carbon strip is formed during cold pressing, and the amount of it increases with increasing milling time and it become much finer. The amount of carbon increased with increasing carbon content under the condition of equal milling time. The cold pressed compact of Cu-2%C had a relative density of 90.4% and a maximum harness of 122HV after 24h milling; the SPS compact showed dense and fine Vmicrostructure, and totally bonded together, and grain took different shape from that of milled powder particles. The relative densities of compacts for the Cu-4%C and Cu-6%C were rather high, reach a maximum value of 98.1%, the maximum hardness was 243HV for the Cu-2%C by milling 24h and SPS at 500℃. 6. A double activation sintering mechanism for the consolidation of C/Cu composite powder was proposed, i.e. the coexistence of mechanical activation induced by high-energy ball mil and discharge activation induced by pulsed current discharge. Their combination led to improvement of properties of compressibility, contact and sintering activity for the C/Cu composite powder, and finally guaranteed the excellent microstructure and mechanical properties. 7. The effects of fabrication techniques on the tribological properties have been investigated; the results reveal that the composites by SPS shows better wear resistance than those by cold pressing. The coefficient of friction and wear rate decreased considerably with increasing carbon content; with increasing the sintering temperature, the coefficient of friction and wear rate just decreased in the same way. XPS analysis of worn surface indicated that better tribological properties were due to formation of a lubricious film covering almost entire worn surface. In the present work, we designed a kind of Cu base composite system with high low-friction and high wear resistance properties, and developed correspondingly processing based on the material composition, overcame the fabrication problem that originated from bad bonding between nano structure layer and substrate and low wetability between carbon and copper. An effective route for optimizing the microstructure of Cu base composite has been developed by combining MA and SPS processings, and its effect on the mechanical properties of the material has been explored. The friction and wear behavior at ambient temperature has been investigated systematically and the wear mechanism has been analyzed, all these works lay a beneficial foundation for the developing novel high strength materials with low-friction and high wear resistance, and for enrichment of materials tribology.
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