The resin-matrix pantograph contact strip (RMPCS),which has excellent abrasion resistance with electrical current and friction-reducing function,was developed in view of the traditional contact strips with high mainte...The resin-matrix pantograph contact strip (RMPCS),which has excellent abrasion resistance with electrical current and friction-reducing function,was developed in view of the traditional contact strips with high maintenance cost,high wear rate with electrical current and severe damage to the copper conducting wire.The characteristics of worn surfaces,cross-section and typical elemental distributions of RMPCS were studied by scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS).The wear behavior and arc discharge of RMPCS against copper were investigated with self-made electrical wear tester.The results show that the electrical current plays a critical role in determining the wear behavior,and the wear rate of the RMPCS against copper with electrical current is 2.7-5.8 times higher than the value without electrical current.The wear rate of the contact strip increases with the increase of the sliding speed and electrical current density.The main wear mechanism of RMPCS against copper without electrical current is low stress grain abrasive and slightly adhesive wear,while arc erosion wear and oxidation wear are the dominate mechanism with electrical current,which is accompanied by adhesive wear during the process of wear.展开更多
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 ...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 composite with dual-lubricant which can work well in both air and vacuum environments and provides a comprehensive analysis on the lubrication mechanisms of the composite.展开更多
Zr/WC composite coating was prepared on the surface of Cr12MoV steel by electric spark deposition technology to change its surface properties. The surface and worn surface morphology of the coating were observed using...Zr/WC composite coating was prepared on the surface of Cr12MoV steel by electric spark deposition technology to change its surface properties. The surface and worn surface morphology of the coating were observed using scanning electron microscope. Dry friction and wear tests of the coatings were carried out at room temperature. The results show that the coating is continuous and uniform, and the thickness was about 50-60 μm. The microhardness of the coating surface was highest at 1140 HV_(200g), which was significantly higher than that of the substrate. The ear tests results show that the wear weight loss, wear volume and wear rate follow the following rules: Cr12MoV>WC coating> Zr/WC composite coating.展开更多
Cu-coated graphite composites were prepared by an electroless plating method,and the composites were examined by scanning electron microscopy(SEM). The copper content of the composites was measured to reach 73%(mass f...Cu-coated graphite composites were prepared by an electroless plating method,and the composites were examined by scanning electron microscopy(SEM). The copper content of the composites was measured to reach 73%(mass fraction). Brush samples made with composites contents of 10%,15% and 20% and with copper powders content of 11% were obtained. The results show that the resistivity of the brush samples decreases and hardness becomes higher with increasing composites content. Copper is dispersively distributed in the brush samples made with the composites,whereas copper agglomerates in Cu-graphite mechanical mixture. For the same Cu content,Cu-coated graphite composites possess lower resistivity and higher hardness than Cu-graphite mechanical mixture. A new type of electric brush was obtained by using Cu-coated graphite composites,the wear and durability tests carried out on a HGH5435M120 AC motor indicate that its service life reaches 250 h. The electric brushes possess relatively low resistivity(275 μΩ·m) and good wear resistance,so they are very suitable for high-speed micromotors.展开更多
CNTs-Ag-G electrical contact composite material was prepared by means of powder metallurgical method. The influence of the graphite content on sliding wear characteristics of electrical contact levels was examined. In...CNTs-Ag-G electrical contact composite material was prepared by means of powder metallurgical method. The influence of the graphite content on sliding wear characteristics of electrical contact levels was examined. In experiments, CNTs content was retained as 1% (mass fraction), and graphite was added at content levels of 8%, 10%, 13%, 15% and 18%, respectively. The results indicate that with the increase of graphite content, the contact resistance of electrical contacts is enhanced to a certain level then remains constant. Friction coefficient decreases gradually with the increase of graphite content. Wear mass loss decreases to the minimum value then increases. With the small content of graphite, the adhesive wear is hindered, which leads to the decrease of wear mass loss, while excessive graphite brings much more worn debris, resulting in the increase of mass loss. It is concluded that wear mass loss reaches the minimum value when the graphite mass fraction is about 13%. Compared with conventional Ag-G contact material, the wear mass loss of CNTs-Ag-G composite is much less due to the obvious increase of hardness and electrical conductivity, decline of friction surface temperature and inhibition of adhesive wear between composites and slip rings.展开更多
An adequate hardness of MoS2/Cu composites has not been achieved if these materials are applied under the extreme wear conditions. Therefore, Me-reinforced MoS2/Cu composites were prepared by powder metallurgy （P/M）...An adequate hardness of MoS2/Cu composites has not been achieved if these materials are applied under the extreme wear conditions. Therefore, Me-reinforced MoS2/Cu composites were prepared by powder metallurgy （P/M） methods. The electrical sliding wear properties in the absence or presence of Mereinforced MoS2/Cu composites were tested by HST-100 high speed electric-tribometer. The hardness, electrical conductivity, density, and microstmcture of MoS2/Cu composites were observed. Me-reinforcement MoS2/Cu composites are of good electrical conductivity, while the hardness of Mo-reinforcedment MoS2/Cu composites is about 33.3% higher than that of MoS2/Cu composites. With the addition of Me, composites show better wear properties under high speed and large electric current due to the improvement of hardness. The effects of current intensity and sliding velocity on the wear properties of the tested materials are complicated, and the wear mechanisms of MoS2/Cu composites are mainly abrasive wear and adhesive wear with arc erosion.展开更多
基金Project (06FJ3041) supported by the Key Laboratory Open Foundation of Hunan Province, China
文摘The resin-matrix pantograph contact strip (RMPCS),which has excellent abrasion resistance with electrical current and friction-reducing function,was developed in view of the traditional contact strips with high maintenance cost,high wear rate with electrical current and severe damage to the copper conducting wire.The characteristics of worn surfaces,cross-section and typical elemental distributions of RMPCS were studied by scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS).The wear behavior and arc discharge of RMPCS against copper were investigated with self-made electrical wear tester.The results show that the electrical current plays a critical role in determining the wear behavior,and the wear rate of the RMPCS against copper with electrical current is 2.7-5.8 times higher than the value without electrical current.The wear rate of the contact strip increases with the increase of the sliding speed and electrical current density.The main wear mechanism of RMPCS against copper without electrical current is low stress grain abrasive and slightly adhesive wear,while arc erosion wear and oxidation wear are the dominate mechanism with electrical current,which is accompanied by adhesive wear during the process of wear.
基金supported by Major Research Program of National Natural Science Foundation of China(Grant No. 91026018)National Natural Science Foundation of China(Grant No. 60979017)Doctoral Fund of Ministry of Education of China(Grant No. 20110111110015)
文摘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 composite with dual-lubricant which can work well in both air and vacuum environments and provides a comprehensive analysis on the lubrication mechanisms of the composite.
基金supported by Key Projects of Strategic International Scientific and Technological Innovation Cooperation(Grant No.2016YFE0201300)
文摘Zr/WC composite coating was prepared on the surface of Cr12MoV steel by electric spark deposition technology to change its surface properties. The surface and worn surface morphology of the coating were observed using scanning electron microscope. Dry friction and wear tests of the coatings were carried out at room temperature. The results show that the coating is continuous and uniform, and the thickness was about 50-60 μm. The microhardness of the coating surface was highest at 1140 HV_(200g), which was significantly higher than that of the substrate. The ear tests results show that the wear weight loss, wear volume and wear rate follow the following rules: Cr12MoV>WC coating> Zr/WC composite coating.
基金Project (59972009) supported by the National Natural Science Foundation of China
文摘Cu-coated graphite composites were prepared by an electroless plating method,and the composites were examined by scanning electron microscopy(SEM). The copper content of the composites was measured to reach 73%(mass fraction). Brush samples made with composites contents of 10%,15% and 20% and with copper powders content of 11% were obtained. The results show that the resistivity of the brush samples decreases and hardness becomes higher with increasing composites content. Copper is dispersively distributed in the brush samples made with the composites,whereas copper agglomerates in Cu-graphite mechanical mixture. For the same Cu content,Cu-coated graphite composites possess lower resistivity and higher hardness than Cu-graphite mechanical mixture. A new type of electric brush was obtained by using Cu-coated graphite composites,the wear and durability tests carried out on a HGH5435M120 AC motor indicate that its service life reaches 250 h. The electric brushes possess relatively low resistivity(275 μΩ·m) and good wear resistance,so they are very suitable for high-speed micromotors.
基金Project(50271021) supported by the National Natural Science Foundation of ChinaProject(ZD2008003) supported by Key Science Foundation of the Education Department of Anhui Province, China+2 种基金Project(CF07-10) supported by the Innovation Center for Postgraduates at HFNL (USTC), ChinaProject(KF0702) supported by the Open Project Program of Ministry of Education of ChinaProject supported by Nippon Sheet Glass Foundation of Japan for Materials Science and Engineering
文摘CNTs-Ag-G electrical contact composite material was prepared by means of powder metallurgical method. The influence of the graphite content on sliding wear characteristics of electrical contact levels was examined. In experiments, CNTs content was retained as 1% (mass fraction), and graphite was added at content levels of 8%, 10%, 13%, 15% and 18%, respectively. The results indicate that with the increase of graphite content, the contact resistance of electrical contacts is enhanced to a certain level then remains constant. Friction coefficient decreases gradually with the increase of graphite content. Wear mass loss decreases to the minimum value then increases. With the small content of graphite, the adhesive wear is hindered, which leads to the decrease of wear mass loss, while excessive graphite brings much more worn debris, resulting in the increase of mass loss. It is concluded that wear mass loss reaches the minimum value when the graphite mass fraction is about 13%. Compared with conventional Ag-G contact material, the wear mass loss of CNTs-Ag-G composite is much less due to the obvious increase of hardness and electrical conductivity, decline of friction surface temperature and inhibition of adhesive wear between composites and slip rings.
基金Funded by the National Natural Science Foundation of China(No:51371077)Non-ferrous Metal Generic Technology of Henan Collaborative Innovation Center
文摘An adequate hardness of MoS2/Cu composites has not been achieved if these materials are applied under the extreme wear conditions. Therefore, Me-reinforced MoS2/Cu composites were prepared by powder metallurgy （P/M） methods. The electrical sliding wear properties in the absence or presence of Mereinforced MoS2/Cu composites were tested by HST-100 high speed electric-tribometer. The hardness, electrical conductivity, density, and microstmcture of MoS2/Cu composites were observed. Me-reinforcement MoS2/Cu composites are of good electrical conductivity, while the hardness of Mo-reinforcedment MoS2/Cu composites is about 33.3% higher than that of MoS2/Cu composites. With the addition of Me, composites show better wear properties under high speed and large electric current due to the improvement of hardness. The effects of current intensity and sliding velocity on the wear properties of the tested materials are complicated, and the wear mechanisms of MoS2/Cu composites are mainly abrasive wear and adhesive wear with arc erosion.
