Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a C...Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a Cu/NbC functionally graded material (FGM) sample were produced by using the two-step press and sintering at 900 °C for 1 h under vacuum. The microstructure and physical and mechanical properties of the specimens were investigated. The field emission scanning electron microscopy, energy dispersive X-ray and X-ray diffraction analysis confirmed the synthesis of the nanostructure matrix of 18–27 nm with the nanoparticles reinforcement of 42 nm after sintering, verifying the thermal stability of this composite at high temperature. The hardness of Cu–15%NbC was five times greater than that of the pure Cu specimen. The volume reduction of the sample after the wear test decreased in comparison with the pure Cu specimen. The electrical conductivity of the composite specimen decreased to 36.68% IACS. The FGM specimen exhibited high electrical conductivity corresponding to 75.83% IACS with the same hardness and wear properties as those of the composite sample on the composite surface. Thus, Cu/NbC FGM with good mechanical and electrical properties can be a good candidate for electrical contact applications.展开更多
New powder metallurgy processing routes were designed to manufacture Ag ZnO electrical contact composites. Their physical properties, electrical contact properties and microstructures were investigated. By modelling ...New powder metallurgy processing routes were designed to manufacture Ag ZnO electrical contact composites. Their physical properties, electrical contact properties and microstructures were investigated. By modelling tests, it is shown that the requirements of commercial use were met. It is proved that Ag ZnO composites could be used to substitute toxic Ag CdO on large load electrical contactors.展开更多
The oxidation properties of silver alloy powders and microstructures of oxidized powders have been investigated by thermo gravity analysis(TGA), scanning electron microscopy(SEM) and wave dispersive X ray spectrosco...The oxidation properties of silver alloy powders and microstructures of oxidized powders have been investigated by thermo gravity analysis(TGA), scanning electron microscopy(SEM) and wave dispersive X ray spectroscopy(WDEX). Ag Sn RE alloy powders have been oxidized completely at 610 ℃ within 60 min, with an external pure silver scale forming around each oxidized particle. It is useful to produce electrical contact composites. The excellent oxidation properties of Ag Sn RE alloy powders are attributed to the ideal microstructure of the oxidized powders.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 a...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
Sliding friction and wear experiments using Cu-La2O3-graphite composites against Cu-5 wt.%Ag alloy ring were conducted at a constant sliding speed of 10 m/s, a current density of 10 A/cm2 and a load of 2.5 N/cm2. Thes...Sliding friction and wear experiments using Cu-La2O3-graphite composites against Cu-5 wt.%Ag alloy ring were conducted at a constant sliding speed of 10 m/s, a current density of 10 A/cm2 and a load of 2.5 N/cm2. These composites with different La2O3 and graphite contents were fabricated by hot-pressing. Physical and mechanical properties of the composites were examined. Morphologies of the worn surface of composites were observed using optical microscopy. X-ray photoelectron spectroscopy spectra were used to study compositions of the lubricating film. The results showed that with the increasing addition of La2O3, hardness, flexural strength and electrical resistivity increased, but the relative density dropped. The friction coefficient increased with the increasing addition of La2O3. Composite containing 3 vol.% of La2O3 and 37 vol.% of graphite showed the best wear resistance. The main wear mechanisms of composites were abrasive wear, oxidative wear and adhesive wear.展开更多
mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing(SPS).The effects of silver powder particle size on the microstructure and properties of the samples were investigated.The surface morphol...mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing(SPS).The effects of silver powder particle size on the microstructure and properties of the samples were investigated.The surface morphologies of the sintered samples were examined by optical microscope(OM),and the fracture morphologies were observed by scanning electron microscopy(SEM).The physical and mechanical properties such as density,electrical resistivity,microhardness,and tensile strength were also tested.The results show that the silver powder particle size has evident effects on the sintered materials.Comparing with coarse silver powder(5 ktm),homogeneous and fme microstmcture was obtained by fine silver powder(_〈0.5-1am).At the same time,the electrical conductivity,microhardness,and tensile strength of the sin-tered samples with fine silver powder were higher than those of the samples with coarse silver powder.However,silver powder particle size has little influence on the relative densities,which of all samples(both by free and coarse silver powders)is more than 95%.The fracture characteristics are ductile.展开更多
Constituents of the oxidized surface film on diamond particles reinforced Cu-Cd alloy matrix composite （Cp/Cu-Cd） were investigated by XPS. The results show that Cu2O is the main constituent when the oxidized film i...Constituents of the oxidized surface film on diamond particles reinforced Cu-Cd alloy matrix composite （Cp/Cu-Cd） were investigated by XPS. The results show that Cu2O is the main constituent when the oxidized film is thin; CuO appears only after the film is rather thick. The originally formed oxidized film on the Cp/Cu-Cd is about 10nm in thickness and is mainly composed of Cu2O and Cu. After oxidized at 120℃ over 30h, CuO is detected in the film.展开更多
Due to their outstanding electrical contact properties,Cd-containing silver-matrix electrical contact materials can meet the requirements of high stability and long life for military defense and aerospace applications...Due to their outstanding electrical contact properties,Cd-containing silver-matrix electrical contact materials can meet the requirements of high stability and long life for military defense and aerospace applications.In order to further reduce the Cd content under the premise of meeting the high-performance requirements,in this study,high-purity intermediate Ti_(2)Cd powder of MAX phase(Ti_(2)CdC)was synthesized with a pressureless technique and then applied to reinforce the Ag matrix.The Cd content of the as-prepared Ag/Ti_(2)Cd composites was actually reduced by 38.31%compared with conventional Ag/CdO material.Based on the systematic study of the effect of heat treatment temperature on the physical phase,morphology,interface and comprehensive physical properties of Ag/Ti_(2)Cd composites,the preferred samples(heat treated at 400°C for 1 h)showed high density(97.77%),low resistivity(2.34μΩ·cm),moderate hardness(90.8HV),high tensile strength(189.9 MPa),and exhibited good electrical contact performance after 40000 cycles of arc discharging under severe conditions(DC 28 V/20 A).The results of microscopic morphological evolution,phase change and elemental distribution of the electrical contact surface show that the combination of high stability of Ti_(2)Cd reinforcing phase,good interfacial bonding with Ag matrix and improved melt pool viscosity in the primary stage of arc erosion,results in low and stable contact resistance(average value 13.20 mΩ)and welding force(average value 0.6 N),low fluctuation of static force(2.2-2.5 N).The decomposition and absorption energy of Ti_(2)Cd and the arc extinguishing effect of Cd vapor are the main reasons for the stable arcing energy and arcing time of electric contacts in the late stage of arc erosion.展开更多
The electric contact material of Ag/SnO2 composite was achieved by reactive synthesis method. The compositions and microstructure of Ag/SnO2 composite were analyzed and characterized by X-ray diffraction （XRD）, scan...The electric contact material of Ag/SnO2 composite was achieved by reactive synthesis method. The compositions and microstructure of Ag/SnO2 composite were analyzed and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and high-resolution electron microscopy （HRTEM）. The struc- tural feature was typical of the particle reinforced composites. The HRTEM images revealed that the observed Ag/SnO2 interface was absence of the precipitated phase and the lattice contrast across the interface was clear and sharp. The average particle size of SnO2 in composite was near 50 nm and it was well dispersed in spherical shape. The thermodynamic mechanism of reactive synthesis method was also discussed. The electronic density distribution analysis of the interface showed the charges of Ag atoms transmitted to 0 atoms and the conductivity of the material was also affected. No extra compounds expected such as AgxOy formed at interface. The distribution of electrons was of inequality near the interface which explained why the mechanical property of the metal/ceramic materials was improved but the machining property declined.展开更多
Efficient and flexible interactions require precisely converting human intentions into computer-recognizable signals,which is critical to the breakthrough development of metaverse.Interactive electronics face common d...Efficient and flexible interactions require precisely converting human intentions into computer-recognizable signals,which is critical to the breakthrough development of metaverse.Interactive electronics face common dilemmas,which realize highprecision and stable touch detection but are rigid,bulky,and thick or achieve high flexibility to wear but lose precision.Here,we construct highly bending-insensitive,unpixelated,and waterproof epidermal interfaces(BUW epidermal interfaces)and demonstrate their interactive applications of conformal human–machine integration.The BUW epidermal interface based on the addressable electrical contact structure exhibits high-precision and stable touch detection,high flexibility,rapid response time,excellent stability,and versatile“cut-and-paste”character.Regardless of whether being flat or bent,the BUW epidermal interface can be conformally attached to the human skin for real-time,comfortable,and unrestrained interactions.This research provides promising insight into the functional composite and structural design strategies for developing epidermal electronics,which offers a new technology route and may further broaden human–machine interactions toward metaverse.展开更多
复合材料的高电阻率会影响飞机原有的导电路径,为保障飞机电气系统的正常运行,需要构建复合材料飞机电气结构网络系统模型来探究其电气特性。首先,针对电磁场下电气结构网络电气特性的计算问题,采用有限元法与稳定双共轭梯度法共同构建...复合材料的高电阻率会影响飞机原有的导电路径,为保障飞机电气系统的正常运行,需要构建复合材料飞机电气结构网络系统模型来探究其电气特性。首先,针对电磁场下电气结构网络电气特性的计算问题,采用有限元法与稳定双共轭梯度法共同构建了电气结构网络系统模型,计算空间消耗量比部分元等效电路(Partial Element Equivalent Circuit,PEEC)法节省了63.92%。其次,通过对多类型激励源/多区域接入点组合的探究,分析了区域阻抗特性、电势分布图谱、电流密度矢量等多维度电学结果及性能影响。通过构建与测量实物模型,对实测结果与仿真结果进行了差异化分析,并验证了实测结果符合适航规章HB 6129。最后,基于实际工况角度与适航规章,对系统模型进行了接触因素系统误差分析、精细化理想模型分析和部件应力因素分析。所获结果及分析对复合材料飞机/电动飞机的电气结构网络的构建具有重要意义。展开更多
基金Sharif University of Technology for the financial support
文摘Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a Cu/NbC functionally graded material (FGM) sample were produced by using the two-step press and sintering at 900 °C for 1 h under vacuum. The microstructure and physical and mechanical properties of the specimens were investigated. The field emission scanning electron microscopy, energy dispersive X-ray and X-ray diffraction analysis confirmed the synthesis of the nanostructure matrix of 18–27 nm with the nanoparticles reinforcement of 42 nm after sintering, verifying the thermal stability of this composite at high temperature. The hardness of Cu–15%NbC was five times greater than that of the pure Cu specimen. The volume reduction of the sample after the wear test decreased in comparison with the pure Cu specimen. The electrical conductivity of the composite specimen decreased to 36.68% IACS. The FGM specimen exhibited high electrical conductivity corresponding to 75.83% IACS with the same hardness and wear properties as those of the composite sample on the composite surface. Thus, Cu/NbC FGM with good mechanical and electrical properties can be a good candidate for electrical contact applications.
文摘New powder metallurgy processing routes were designed to manufacture Ag ZnO electrical contact composites. Their physical properties, electrical contact properties and microstructures were investigated. By modelling tests, it is shown that the requirements of commercial use were met. It is proved that Ag ZnO composites could be used to substitute toxic Ag CdO on large load electrical contactors.
文摘The oxidation properties of silver alloy powders and microstructures of oxidized powders have been investigated by thermo gravity analysis(TGA), scanning electron microscopy(SEM) and wave dispersive X ray spectroscopy(WDEX). Ag Sn RE alloy powders have been oxidized completely at 610 ℃ within 60 min, with an external pure silver scale forming around each oxidized particle. It is useful to produce electrical contact composites. The excellent oxidation properties of Ag Sn RE alloy powders are attributed to the ideal microstructure of the oxidized powders.
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Project supported by the Major Research Program of the National Natural Science Foundation of China(91026018)the Doctoral Fund of Ministry of Education of China(2011011110015)the Shanghai City special artificial micro materials and Technology Key Laboratory Open Fund(ammt2013A-7)
文摘Sliding friction and wear experiments using Cu-La2O3-graphite composites against Cu-5 wt.%Ag alloy ring were conducted at a constant sliding speed of 10 m/s, a current density of 10 A/cm2 and a load of 2.5 N/cm2. These composites with different La2O3 and graphite contents were fabricated by hot-pressing. Physical and mechanical properties of the composites were examined. Morphologies of the worn surface of composites were observed using optical microscopy. X-ray photoelectron spectroscopy spectra were used to study compositions of the lubricating film. The results showed that with the increasing addition of La2O3, hardness, flexural strength and electrical resistivity increased, but the relative density dropped. The friction coefficient increased with the increasing addition of La2O3. Composite containing 3 vol.% of La2O3 and 37 vol.% of graphite showed the best wear resistance. The main wear mechanisms of composites were abrasive wear, oxidative wear and adhesive wear.
文摘mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing(SPS).The effects of silver powder particle size on the microstructure and properties of the samples were investigated.The surface morphologies of the sintered samples were examined by optical microscope(OM),and the fracture morphologies were observed by scanning electron microscopy(SEM).The physical and mechanical properties such as density,electrical resistivity,microhardness,and tensile strength were also tested.The results show that the silver powder particle size has evident effects on the sintered materials.Comparing with coarse silver powder(5 ktm),homogeneous and fme microstmcture was obtained by fine silver powder(_〈0.5-1am).At the same time,the electrical conductivity,microhardness,and tensile strength of the sin-tered samples with fine silver powder were higher than those of the samples with coarse silver powder.However,silver powder particle size has little influence on the relative densities,which of all samples(both by free and coarse silver powders)is more than 95%.The fracture characteristics are ductile.
文摘Constituents of the oxidized surface film on diamond particles reinforced Cu-Cd alloy matrix composite （Cp/Cu-Cd） were investigated by XPS. The results show that Cu2O is the main constituent when the oxidized film is thin; CuO appears only after the film is rather thick. The originally formed oxidized film on the Cp/Cu-Cd is about 10nm in thickness and is mainly composed of Cu2O and Cu. After oxidized at 120℃ over 30h, CuO is detected in the film.
基金This work was financially supported by the National Natural Science Foundation of China(52101064)Jiangsu Planned Projects for Postdoctoral Research Funds(2020Z158)Industry-University-Research Cooperation Projects(RH2000002728,RH2000002332,RH2100000263).
文摘Due to their outstanding electrical contact properties,Cd-containing silver-matrix electrical contact materials can meet the requirements of high stability and long life for military defense and aerospace applications.In order to further reduce the Cd content under the premise of meeting the high-performance requirements,in this study,high-purity intermediate Ti_(2)Cd powder of MAX phase(Ti_(2)CdC)was synthesized with a pressureless technique and then applied to reinforce the Ag matrix.The Cd content of the as-prepared Ag/Ti_(2)Cd composites was actually reduced by 38.31%compared with conventional Ag/CdO material.Based on the systematic study of the effect of heat treatment temperature on the physical phase,morphology,interface and comprehensive physical properties of Ag/Ti_(2)Cd composites,the preferred samples(heat treated at 400°C for 1 h)showed high density(97.77%),low resistivity(2.34μΩ·cm),moderate hardness(90.8HV),high tensile strength(189.9 MPa),and exhibited good electrical contact performance after 40000 cycles of arc discharging under severe conditions(DC 28 V/20 A).The results of microscopic morphological evolution,phase change and elemental distribution of the electrical contact surface show that the combination of high stability of Ti_(2)Cd reinforcing phase,good interfacial bonding with Ag matrix and improved melt pool viscosity in the primary stage of arc erosion,results in low and stable contact resistance(average value 13.20 mΩ)and welding force(average value 0.6 N),low fluctuation of static force(2.2-2.5 N).The decomposition and absorption energy of Ti_(2)Cd and the arc extinguishing effect of Cd vapor are the main reasons for the stable arcing energy and arcing time of electric contacts in the late stage of arc erosion.
基金supported by the National Natural Science Foundation of China (Nos. 2008CB617609,u0837601, u0837603 and 50874054)the Science Innovation Foundation of Kunming University of Science and Technology
文摘The electric contact material of Ag/SnO2 composite was achieved by reactive synthesis method. The compositions and microstructure of Ag/SnO2 composite were analyzed and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and high-resolution electron microscopy （HRTEM）. The struc- tural feature was typical of the particle reinforced composites. The HRTEM images revealed that the observed Ag/SnO2 interface was absence of the precipitated phase and the lattice contrast across the interface was clear and sharp. The average particle size of SnO2 in composite was near 50 nm and it was well dispersed in spherical shape. The thermodynamic mechanism of reactive synthesis method was also discussed. The electronic density distribution analysis of the interface showed the charges of Ag atoms transmitted to 0 atoms and the conductivity of the material was also affected. No extra compounds expected such as AgxOy formed at interface. The distribution of electrons was of inequality near the interface which explained why the mechanical property of the metal/ceramic materials was improved but the machining property declined.
基金supported by National Natural Science Foundation of China(52202117,52232006,52072029,and 12102256)Collaborative Innovation Platform Project of Fu-Xia-Quan National Independent Innovation Demonstration Zone(3502ZCQXT2022005)+3 种基金Natural Science Foundation of Fujian Province of China(2022J01065)State Key Lab of Advanced Metals and Materials(2022-Z09)Fundamental Research Funds for the Central Universities(20720220075)the Ministry of Education,Singapore,under its MOE ARF Tier 2(MOE2019-T2-2-179).
文摘Efficient and flexible interactions require precisely converting human intentions into computer-recognizable signals,which is critical to the breakthrough development of metaverse.Interactive electronics face common dilemmas,which realize highprecision and stable touch detection but are rigid,bulky,and thick or achieve high flexibility to wear but lose precision.Here,we construct highly bending-insensitive,unpixelated,and waterproof epidermal interfaces(BUW epidermal interfaces)and demonstrate their interactive applications of conformal human–machine integration.The BUW epidermal interface based on the addressable electrical contact structure exhibits high-precision and stable touch detection,high flexibility,rapid response time,excellent stability,and versatile“cut-and-paste”character.Regardless of whether being flat or bent,the BUW epidermal interface can be conformally attached to the human skin for real-time,comfortable,and unrestrained interactions.This research provides promising insight into the functional composite and structural design strategies for developing epidermal electronics,which offers a new technology route and may further broaden human–machine interactions toward metaverse.
文摘复合材料的高电阻率会影响飞机原有的导电路径,为保障飞机电气系统的正常运行,需要构建复合材料飞机电气结构网络系统模型来探究其电气特性。首先,针对电磁场下电气结构网络电气特性的计算问题,采用有限元法与稳定双共轭梯度法共同构建了电气结构网络系统模型,计算空间消耗量比部分元等效电路(Partial Element Equivalent Circuit,PEEC)法节省了63.92%。其次,通过对多类型激励源/多区域接入点组合的探究,分析了区域阻抗特性、电势分布图谱、电流密度矢量等多维度电学结果及性能影响。通过构建与测量实物模型,对实测结果与仿真结果进行了差异化分析,并验证了实测结果符合适航规章HB 6129。最后,基于实际工况角度与适航规章,对系统模型进行了接触因素系统误差分析、精细化理想模型分析和部件应力因素分析。所获结果及分析对复合材料飞机/电动飞机的电气结构网络的构建具有重要意义。
