Four kinds of Cu-based composites with different mass ratios of graphite and WS2 as lubricants were fabricated by hot-pressing method. Electrical sliding wear behaviors of the composites were investigated using a block-on-ring tribometer rubbing against Cu-5%Ag alloy ring. The results demonstrated that 800 ~C was the optimum sintering temperature for Cu-graphite-WS2 dual-lubricant composites to obtain the best comprehensive properties of mechanical strength and lubrication performance. Contact voltage drops of the Cu-based composites increased with increasing the mass ratio of WS2 to graphite. The Cu-based composite with 20% graphite and 10% WS2 showed the best wear resistance due to the excellent synergetic lubricating effect of graphite and WS2. The reasonable addition of WS2 into the Cu-graphite composite can remarkably improve the wear resistance without much rise of electrical energy loss which provides a novel principle of designing suitable sliding electrical contact materials for industrial applications.
Multi-walled carbon nanotubes （MWCNTs） were irradiated with focused electron beams in a transmission electron microscope at room temperature. The results showed that carbon nanotubes had no obvious structural damages but only shell bending under 100 keV electron beam irradiation. However, when the electron energy increased to 200 keV, the nanotubes were damaged and amorphization, pits and gaps were detected. Furthermore, generating of carbon onions and welding between two MWCNTs occurred under 200 keV electron irradiation. It was easy to destroy the MWCNTs as the electron beams exceeded the displacement threshold energy that was calculated to be 83-110 keV. Conversely, the energy of electron beams below the threshold energy was not able to damage the tubes. The damage mechanism is sputtering and atom displacement.
In this paper Cu-WS2-graphite-WS2nanotube composites were fabricated by powder metallurgy hot pressing method.The effect of current polarity on the wear rates and contact voltage drops of the composites were investigated using a brush-on-slip ring tribometer rubbing against Cu-5 wt.%Ag alloy ring in air and vacuum,respectively.The worn surfaces of the composites were analyzed by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).Surface profile curves of the worn tracks were measured using the surface profiler.The results demonstrated that the current polarity has a significant effect on the wear rates and contact voltage drops of the composites in both air and vacuum conditions.Positive brush possesses a higher wear rate compared with the negative brush in the air atmosphere since the electrical field direction activates oxidation at the positive brush surface while inhibits oxidation at the negative brush surface.Except for the regular wear losses,the combined effect of molten metal bridge erosion and arc erosion cause the positive brush to lose extra material and the negative brush to gain extra material,so the positive brush shows a higher wear rate in the vacuum condition.The contact voltage drop of the positive brush is lower than that of the negative brush in the air atmosphere,but contrarily,the positive brush shows a higher contact voltage drop in the vacuum condition.
Cu-based self-lubricating materials containing two different solid lubricants （graphite and MoSs） were fabricated by P/M hot pressing techniques. Physical and mechan- ical properties of the samples were examined. The effects of graphite and MoSs contents on friction coefficient and wear rate were investigated by a ring-on-disc wear machine in air and vacuum conditions, respectively. Tribo-films formed on the worn surfaces were characterized by scanning electron microscopy （SEM） and X-ray photo- electron spectroscopy （XPS）. The results indicated that density, hardness and bending strength all increased with the increasing content of MoS2, while the relative density was opposite. Sample B containing 15 vol. pct graphite and 15 vol. pct MoS2 pos- sessed superior tribological properties both in air and vacuum conditions. However, the tribo-films formed on the worn surfaces of the sample B were greatly discrepant in composition at different testing conditions. In air, the volume ratio of MoS2 and graphite in the tribo-films is 0.31：1 whereas the ratio in vacuum is 1.07：1.
Shiyin HUANG Yi FENG Kewang DING Gang QIAN Hongjuan LIU Yang WANG
As the traditional graphite-based composites cannot meet the requirement of rapid developing modern industry, novel sliding electrical contact materials with high self-lubricating performance in multiple environments are eagerly required. Herein a copper-based composite with WS2 and graphite as solid lubricant are fabricated by powder metallurgy hot-pressed method. The friction and wear behaviors of the composites with and without current are investigated under the condition with sliding velocity of 10 m/s and normal load of 2.5N/cm 2 in both air and vacuum. Morphologies of the worn surfaces are observed by optical microscope and compositions of the lubricating films are analyzed by XPS. Surface profile curves and roughness of the worn surfaces are obtained by 2205 surface profiler. The results of wear tests show that the friction coefficient and wear volume loss of the composites with current are greater than that without current in both air and vacuum due to the adverse effects of electrical current which damaged the lubricating film partially and roughed the worn surfaces. XPS results demonstrate that the lubricating film formed in air is composed of oxides of Cu, WS2 , elemental S and graphite, while the lubricating film formed in vacuum is composed of Cu, WS2 and graphite. Because of the synergetic lubricating action of oxides of Cu, WS2 and graphite, the composites show low friction coefficient and wear volume loss in air condition. Owing to the fact that graphite loses its lubricity which makes WS2 become the only lubricant, severe adhesive and abrasive wear occur and result in a high value of wear rate in vacuum condition. The formation of the lubricating film on the contact interface between the brush and ring is one of the factors which can greatly affect the wear performance of the brushes. The low contact voltage drop of the composites in vacuum condition is attributed to the high content of Cu in the surface film. This study fabricated a kind of new sliding electrical contact self-lubricating composi
QIAN GangFENG YiLI BinHUANG ShiyinLIU HongjuanDING Kewang
