Lubrication performance of graphene in the sliding electrical contact interface

Electrical contact materials are increasingly widely used,but the existing electric contact lubricants still have lots of room for improvement,such as anti-wear performance and lubrication life.Due to the excellent electrical and lubrication properties,graphene shows great potential in lubricating the sliding electrical contact interface,but there is a lack of relevant research.Some researchers have studied the lubrication performance of graphene between the gold-coated/TiN-coated friction pair at an ultra-low current.However,the lubrication performance of graphene on more widely used electrical contact materials such as copper and its alloys under larger and more commonly used current or voltage conditions has not been reported.In this paper,we study the lubrication performance of graphene in the copper and its alloys sliding electrical contact interface under usual parameters,which is explored through four aspects:different substrates-copper and brass,different test methods-constant voltage and constant current,different normal loads and durability test.The experiments demonstrate that graphene can significantly reduce the friction and wear on brass and copper under the above test methods and parameters,with low contact resistance at the same time.Our work is expected to provide a new lubricant for electrical contact materials and contribute to enriching the tribological theory of graphene.

THE INVESTIGATION OF CONTACT RESISTANCE CHARACTERISTICS ON ELECTRICAL CONTACTS USED IN COAL MINES

Based on the electrical contact and arc theory, the experiments on contact resistance characteristics of electrical contacts are carried out, by analyzing the experimental results, some conclusions of contact resistance characteristics have been obtained in this paper.

Effects of Rare Earths on Electrical Conductivity, Melting-Welding and Corrosion Resistance by Electric Arc of Copper-Based Alloys

The effects of rare earths on electric conductivity fusion welding-resistance and erosion-resistance by electric arc of copper-based compound material by adding different amount of rare earths to copper base to get copper based compound materials were studied. Rare earths improve active ability among interfaces and optimize organizational structures. The conductivity of samples with rare earths is obviously better than that of materials without them. Moreover, wear ability and oxidization resistance of materials with rare earths can be improved greatly. For copper contact head with rare earths, electric arc corrosion resistance and welding-melting resistance are improved. Such alloys also decrease resistance change with increasing temperature. But the adding quantity of rare earths should be appropriate and formed handicraft should be properly regulated.

Prediction of contact resistance of electrical contact wear using different machine learning algorithms

H62 brass material is one of the important materials in the process of electrical energy transmission and signal transmission,and has excellent performance in all aspects.Since the wear behavior of electrical contact pairs is particularly complex when they are in service,we evaluated the effects of load,sliding velocity,displacement amplitude,current intensity,and surface roughness on the changes in contact resistance.Machine learning(ML)algorithms were used to predict the electrical contact performance of different factors after wear to determine the correlation between different factors and contact resistance.Random forest(RF),support vector regression(SVR)and BP neural network(BPNN)algorithms were used to establish RF,SVR and BPNN models,respectively,and the experimental data were trained and tested.It was proved that BP neural network model could better predict the stable mean resistance of H62 brass alloy after wear.Characteristic analysis shows that the load and current have great influence on the predicted electrical contact properties.The wear behavior of electrical contacts is influenced by factors such as load,sliding speed,displacement amplitude,current intensity,and surface roughness during operation.Machine learning algorithms can predict the electrical contact performance after wear caused by these factors.Experimental results indicate that an increase in load,current,and surface roughness leads to a decrease in stable mean resistance,while an increase in displacement amplitude and frequency results in an increase in stable mean resistance,leading to a decline in electrical contact performance.To reduce testing time and costs and quickly obtain the electrical contact performance of H62 brass alloy after wear caused by different factors,three algorithms(random forest(RF),support vector regression(SVR),and BP neural network(BPNN))were used to train and test experimental results,resulting in a machine learning model suitable for predicting the stable mean resistance of H62 brass alloy after wear.The prediction results showed that the BPNN model performed better in predicting the electrical contact performance compared to the RF and SVR models.

Integration of Seismic Refraction and 2D Electrical Resistivity in Locating Geological Contact

The aim of this research is to locate the geological contact for engineering purpose applying seismic refraction and 2D electrical resistivity method. Resistivity and seismic refraction method was conducted on four survey lines with 3 lines running from NW to SE which about parallel to each other and 40 m apart while the fourth line was running from SW to NE. The 2D resistivity survey used minimum electrode spacing of 5 m and the survey used pole-dipole array with minimum current was 2 mA and maximum was 20 mA. The seismic refraction survey used 5 m geophone spacing with offset shot was + 30 m and - 30 m. Resistivity results generally show the area was divided into two main zones, alluvium with resistivity value of 10 - 800 ohm-m, and granite bedrock with resistivity value of > 2500 ohm-m. There is a geological contact between granite and alluvium. The seismic results show the area consists of two layers. The first layer (top layer) with velocity of 460 - 900 m/s which was alluvium mixed with boulders. The second layer with velocity of 2060 - 3140 m/s with depth 71 - 90 MSL. The thickness of the overburden is 5 - 15 m.

The Electrical Resistivity of Cement Paste Incorporated with Retarder

A non contacting electrical resistivity measurement device was used for measuring the electrical resistivity of cement paste incorporated with retarder.The hydration process was divided into dissolving period,setting period,hardening period.With the increase of the retarder,the dissolution time will increase.The setting time happens between minimum point time and inflexion point time based on the electrical resistivity curve.The strength isoline was proposed to predict the strength trend.

Evolution of the electrical contact of dynamic pantograph–catenary system

A good contact between the pantograph and catenary is critically important for the working reliability of electric trains, while the basic understanding on the electrical contact evolution during the pantograph--catenary system working is still ambiguous so far. In this paper, the evolution of electric contact was studied in respects of the contact resistance, temperature rise, and microstructure variation, based on a home-made pantograph-catenary simulation system. Pure carbon strips and copper alloy contact wires were used, and the experimental electrical current, sliding speed, and normal force were set as 80 A, 30 km/h, and 80 N, respectively. The contact resistance presented a fluctuation without obvious regularity, concentrating in the region of 25 and 50 mf~. Temperature rise of the contact point experienced a fast increase at the first several minutes and finally reached a steady state. The surface damage of carbon trips in microstructure analysis revealed a complicated interaction of the sliding friction, joule heating, and arc erosion.

Influence of the ambient air temperature on the electrical contact reliability of electromagnetic relay

The dynamic contact resistances of HH52P electromagnetic relays are measured under different ambient air tem- perature. Their diagnostic parameters are extracted and determined. It is found that the ambient air temperature obviously influ- ences some parameters. In order to research its influence on the electrical contact reliability of electromagnetic relay, the statistic analysis is applied to study the static contact resistance, the max of the dynamic contact resistance and the bounce time. It is found that the ambient air temperature regularly influences the three parameters. Thoroughly, the phenomenon is studied and analyzed in the point of material science so as to probe into the essential matter of it.

Influence of graphite content on sliding wear characteristics of CNTs-Ag-G electrical contact materials

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.

Characterization of low-resistance ohmic contacts to heavily carbon-doped n-type InGaAsBi films treated by rapid thermal annealing

Carbon-doped In Ga As Bi films on In P:Fe(100)substrates have been grown by gas source molecular beam epitaxy(GSMBE).The electrical properties and non-alloyed Ti/Pt/Au contact resistance of n-type carbon-doped In Ga As Bi films were characterized by Van der Pauw-Hall measurement and transmission line method(TLM)with and without rapid thermal annealing(RTA).It was found that the specific contact resistance decreases gradually with the increase of carrier concentration.The electron concentration exhibits a sharp increase,and the specific contact resistance shows a noticeable reduction after RTA.With RTA,the In Ga As Bi film grown under CBr4 supply pressure of 0.18 Torr exhibited a high electron concentration of 1.6×10^(21) cm^(-3) and achieved an ultra-low specific contact resistance of 1×10^(-8)Ω·cm^(2),revealing that contact resistance depends greatly on the tunneling effect.

Evaluation of the Electrical Contact Area at the SOFC Cathode

In the frame of the ZeuS-Ill project, a model study was started on evaluation the area-specific resistances （ASRs） of various layers being used in SOFC stacks. It is well known that stack performance not only depends on cell resistance but also on the electrical conductivity of the various applied contact and protective layers. Various layers have been tested under simulated SOFC conditions, and results have shown that the lowest ASR value, about 3 mΩ.cm2, was obtained for an LSM （2） contact layer. A significantly higher resistance was found for the combined contact and protective layer LCC10-Mn3O4, being around 37 mΩ.cm2 Related to the various tests, the total ASR of an F-design stack, developed by Forschungszentrum Jiilich, under ideal conditions can be estimated. In this case the ASR value was calculated as the sum of that of the LCC10-Mn3O4 layer and the formed oxide scale due to oxidation of Crofer22APU. Contacting resistance at the anode side was considered negligible. When differences in the ASR values occurred when compared with that from current-voltage measurements performed with real SOFC stacks, this can be explained by the limited contact area between interconnect and cathode. These results can be used to model the influence of various applied layers and different geometric contact areas on the overall ASR as determined from performance measurements with SOFC stacks.

A New Characterization Approach of Weld Nugget Growth by Real-Time Input Electrical Impedance

The in-process changes of weld nugget growth during the Resistance Spot Welding were investigated based on the resistance of input electrical impedance. To compute the time varying resistance of input electrical impedance, the welding voltage and current signals are measured simultaneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying resistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nugget growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions.

Relation between viscoplastic flow, periodic feature and Joule heat validity for electrically assisted friction stir welding

Electrically assisted friction stir welding is a promising way to improve liquidity of viscoplastic metal. However, this local heat source only can take into effect in a certain contact interface status. Semi-analytical model and FEM are adopted to analyze materials flow in electrically assisted FSW. Semi-analysis results show that Joule heating is validity with rotation speed 1 400 r/min and travel speed 400 mm/min. The maximum flow velocity is 0.033 m/s when travel speed is 400 mm/min, and it increases to 0.043 m/s with current assistant. Visco-plasticizing efficiency is a key factor to decide whether Joule heat is significant, and viscoplastic flow can periodically make circuit short. Periodic torque, axial force and onion rings surface show dynamic flow process, which can be used to illustrate the dynamic contact resistance feature and correct the calculation equation of Joule heat. This paper is aim to point out the potential relation between viscoplastic flow, periodic torque and Joule heating validity.

基于电接触强化的铝合金表面电刷镀镍层改性研究

[目的]对铝合金进行表面处理可提高其硬度和耐磨性,拓宽铝合金材料在机械零件方面的应用。[方法]采用电刷镀技术在1060铝合金表面制备Ni镀层,再通过电接触强化技术对Ni镀层进行改性。采用扫描电子显微镜和维氏硬度计考察了Ni镀层电接触强化前后的微观组织和显微硬度。通过摩擦磨损试验对比了1016铝合金及Ni镀层电接触强化前后的耐磨性。[结果]经电接触强化后,Ni镀层内部的裂纹及孔洞类缺陷减少,晶粒间隙减小,致密性提高,显微硬度增大到524.4~560.3 HV0.1范围内。1016铝合金在摩擦磨损试验后存在较深的犁沟和剥落,耐磨性较差。Ni镀层的耐磨性优于1016铝合金,但在摩擦过程中会发生剥落。经电接触强化的Ni镀层在摩擦过程中摩擦因数平稳,表面只是轻微擦伤,耐磨性最佳。[结论]结合电刷镀镍和电接触强化技术可显著提高铝合金的表面性能。

结构参数对电连接器接触性能的影响及优化

接触电阻是直接反映电连接器接触性能的主要因素之一。为研究片簧式电连接器的公母端子过盈量、簧片片宽、簧片悬臂梁长度、簧片厚度四种结构参数对接触电阻的影响,基于赫兹接触理论建立电连接器接触电阻的理论计算模型,并利用ABAQUS对接触电阻进行仿真分析,设计了正交试验对某款电连接器四种结构参数进行优化,并得到了四种结构参数对接触电阻影响的显著性水平。试验结果表明:片簧式电连接器四种结构参数中簧片悬臂梁长度、簧片厚度对其影响更为显著;且公母端子过盈量和簧片片宽与接触电阻呈线性变化、簧片悬臂梁长度和簧片厚度与接触电阻呈抛物线变化;电连接器结构参数优化后接触电阻减小了7.52%。

基于电流监测和动态电阻分析的电容器组SF_(6)断路器电寿命评估系统

电容器组SF_(6)断路器电寿命状态监测工作对保障电网安全可靠运行意义重大。文中融合触头磨损计算方法和动态电阻分析法对SF_(6)断路器电寿命进行评估,提出SF_(6)断路器电寿命评估判据,首先基于断路器电流监测数据计算断路器触头磨损,对断路器电寿命状态进行判断预测,再利用动态电阻分析法印证判断出SF_(6)断路器的真实状态,兼顾触头磨损计算法的实时性和动态电阻法的准确性。基于所提判据,研发了一套融合触头磨损和动态电阻的SF_(6)断路器电寿命评估系统。该系统可基于断路器投切数据和动态电阻准确地评估SF_(6)断路器的电寿命,同时在人机交互界面上直观地呈现结果,为工作人员进行断路器状态检修提供辅助决策。

Ag/Cr_(2)AlC电接触材料的微观组织与耐电弧侵蚀性能

Ag基电接触材料被广泛应用于低压电路控制器件中,在电路中起承载、分断、闭合电流的作用。Cr_(2)AlC作为M_(n+1)AX_(n)相的典型代表之一,兼具金属和陶瓷的优良性能,有望成为Ag基电接触材料中优良的增强相。本项目采用粉末冶金法制备Ag/Cr_(2)AlC复合材料,表征其微观组织,探究其界面反应,并研究材料的物理性能和耐电弧侵蚀性能。结果表明,由于Al原子的弱结合,经烧结,Ag与Cr_(2)AlC发生明显的界面反应,生成Ag_(3)Al和Cr-C化合物。相比于生坯,Ag/Cr_(2)AlC熟坯的密度和硬度下降,分别为9.04 g/cm^(3)和(78.9±5.5)HV,且由于界面反应的发生,材料的电阻率为(141.9±0.4)×10^(-9)Ω·m。电弧侵蚀结果表明,Ag/Cr_(2)AlC材料经电弧侵蚀生成Al_(2)O_(3),Ag发生熔融喷溅,产生明显凸起,Ag/Cr_(2)AlC的质量损失为6.25%。

AZ91D镁合金表面钼-钛-锰导电膜化学转化工艺及其性能研究

[目的]对镁合金进行表面处理可获得兼具导电性和耐蚀性的膜层,进而满足电子通信领域的使用要求。[方法]采用以(NH_(4))_(2)MoO_(4)、H_(2)TiF_(6)和KMnO_(4)为主成分的溶液,在AZ91D镁合金表面通过化学转化技术制备了钼−钛−锰(用MTM表示)导电膜。研究了前处理工艺和化学转化液的KMnO_(4)质量浓度对MTM膜层外观、形貌、组成、耐蚀性和导电性的影响。[结果]对AZ91D镁合金进行打磨、碱洗、酸洗、表调等前处理后在含4.2 g/L KMnO_(4)的转化液中处理所得的MTM膜层表面拥有最大面积分数的β相导电斑点,耐蚀性较好,导电性最佳(禁带宽度和接触电阻分别为2.556 eV和0.428Ω/in^(2))。[结论]本工艺制备的MTM膜层耐蚀性和导电性良好,在电子通信领域具有很好的应用前景。

超高速滑动电接触CuCrZr合金轨道表面磨损机制及电接触性能

电磁轨道发射具有典型超高速滑动电接触特性(出口速度大于等于2000 m/s),电磁轨道表面会发生磨损。为研究轨道表面磨损状态与接触电阻之间关系,通过开展电磁轨道发射试验,研究发射后的CuCrZr轨道表面沉积层的形成与磨损机制,揭示枢轨间静态接触电阻的演变规律,总结沉积层的形成与接触电阻的关联关系。结果表明:沿着发射方向,轨道表面沉积层覆盖面积逐渐增大,沉积层的形成机制由摩擦材料转移变为电枢表面熔化飞溅,表面磨损特征由机械磨损向电气磨损转变;由于轨道不同位置沉积层形成原因不同,导致表面粗糙度分布不一致,枢轨间静态接触电阻随接触沉积层形貌特征改变呈现上升、下降及波动3个变化阶段;并且枢轨间静态接触电阻随着接触压力的增大而减小。研究成果对电磁轨道发射装备的研究及发射动力学研究具有理论价值。

抛光工艺对平面与球面铆钉电触头接触电阻的影响

研究了在两种抛光工艺下对平面、球面铆钉电触头接触电阻的影响。抛光工艺使用钢针磨和球磨两种工艺。结果表明:在同种铆钉规格下,球磨抛光工艺的粗糙度低于钢针抛光工艺的粗糙度,球磨抛光工艺的接触电阻低于钢针抛光工艺的接触电阻,且抛光工艺对平面铆钉电触头的接触电阻影响较大,这与抛光工艺对表面粗糙度的影响有关。