Arc Erosion Research Articles

Tribological behavior and wear mechanism of Cu/CF/phenolic resin sandwich composites under current

The catenary system was an important part of electrified railway, which provided traction power for electric trains. Cu/CF/phenolic resin contact strip (CFRCS) had been designed with excellent mechanical strength and electrical conductivity. The properties of CFRCS and the pure carbon contact strip (PCCS) were also compared. It could be found that CFRCS not only had higher impact strength than PCCS, but also had lower resistivity, which was favorable for current transmission. This paper analyzed the wear behavior of contact strips from two aspects of wear data and abrasive dust, which was mainly determined by the current and its components. The current-carrying wear mechanism of CFRCS was mainly arc erosion wear, oxidation wear and adhesive wear, while that of PCCS was oxidation wear and arc erosion wear.

Chromium, a promising cathode candidate for homogeneous arc erosion in air

Cathode erosion hinders the development of high-power arc heaters, and the inhomogeneous erosion of the copper cathode results in catastrophic failures. In this work, the arc erosion behavior of a chromium cathode was investigated compared with copper. The former was relatively homogeneous with shallow erosion pits. The eroded microstructure suggests that the surface chromic oxide layer could suppress the formation of deep craters. The maximum erosion depth and the erosion rate of chromium were lower than those of copper. The single erosion pits on chromium gradually extended and disappeared, suggesting a reduction in the input energy flux density. The underlying mechanism for the homogeneous erosion behavior of the chromium cathode was proposed. The homogeneous erosion behavior of the chromium cathode makes it a promising candidate for high-power arc heaters.

Preparation and arc erosion behavior of AgNi10 contact material with different allotropes of carbon addition

AgNi10 contact materials adding carbon nanotubes (CNTs), nanographene sheets (GNPs), and graphite(Gr) were fabricated via powder metallurgy method. To investigate the influence of different allotropes of carbon addition on microstructure and properties of AgNi10 contacts, the arc erosion behavior was tested under a DC resistive load of 24V/20A. The results indicate that uniformly dispersed CNTs and GNPs present obvious strengthening effect while Gr leads to strength reduction of AgNi10 contacts. The contacts adding CNTs and GNPs show well-scattered and stable arc. Material transfer from cathode to anode was observed but the mass change is less than that of the contact without addition. The contacts with CNTs and GNPs addition show smooth surface without deep crater on the cathode or sharp tip on the anode. Moreover, no obvious splash of molten Ag and Ni was observed. Anti-welding performance is improved with all the carbon allotropes. The contact added GNPs presents the best arc erosion performance with average arc time as 14.7 ms, average contact resistance as 4.51mΩ, and maximum welding force as 38cN.

Fabrication and experimental investigation of arc erosion behavior in W/Cu functionally graded composites

In this study, a functionally graded composite (FGC) technique is proposed to produce an electrical contact material made of W/Cu alloy. The prepared composite was sintered and subjected to high-voltage vacuum arc erosion. The composite properties and microstructure are carefully studied based on SEM images before and after exposure to vacuum arc discharge. According to the necking phenomenon observed in the electron micrographs and the quantitative analysis of the particle size, it is evident that the intermediate layer of W/Cu FGC has been in the final stage of the sintering process. The present porosity of FGC samples was less than mono-layered composite (MLC) samples, and the minimum porosity was observed in the three-layered FGC that composed of W70/Cu30 in the first layer. The average hardness of FGC samples was 4% higher than that of MLC samples with an identical composition. The results of the erosion behavior assessment were used to determine the possible arc erosion mechanism. The weight loss was diminished upon erosion when the W/Cu alloys had more than one layer, especially in four-layered FGC. The result also revealed that FGC samples, especially the four-layered composite, had improved heat transfer and prevented heat concentration on the contact surfaces due to higher content of Cu particles in the successive layers and consequently reduced the surface damage.

Comparison of the interfacial reactions and properties between Ag/Ti3AlC2 and Ag/Ti3SiC2 electrical contact materials

Ag/Ti3AlC2 and Ag/Ti3SiC2 composites are promising candidates for electrical contact applications. However, it is necessary to clarify the influence of structural stability of MAX phases on the properties of Ag-based composites to further improve their arc erosion resistance. Herein we report the preparation, interfacial reactions, physical properties as well as the arc erosion resistances of these two composites. The interfacial reaction between Ag and Ti3AlC2 by deintercalation of Al from Ti3AlC2 is identified, while that between Ag and Ti3SiC2 is hardly detected. The formation of the intermetallic compound between Ag and the weakly bonded Al element in Ti3AlC2 decreases the reaction enthalpy of Ag and Ti3AlC2 significantly and promotes the interfacial reaction in Ag/Ti3AlC2, which are confirmed by the first-principles calculations. The sintered Ag/Ti3SiC2 shows lower resistivity and hardness than Ag/Ti3AlC2 because of its weak interfacial reaction. Superior arc erosion resistance of Ag/Ti3SiC2 is obtained, resulting from the relatively stable Ti3SiC2 and the lower resistivity of the composite. The present work elucidates the designing and optimizing strategies for Ag/MAX composites.

Effect of TiB2 particle size on the material transfer behaviour of Cu–TiB2 composites

Cu-5.8vol.-%TiB2 composites reinforced with different sized TiB2 particles were prepared by spark plasma sintering (SPS). The arc erosion resistance was examined using a JF04C electrical contact instrument. The results indicate that the TiB2 particle size and contact currents have important effects on the material transfer mode. Both lower mass loss and relative mass transfer was observed in the Cu-5.8vol.-%TiB2 composites reinforced with fine TiB2 particles (10 um, 30 um) compared to those with coarse TiB2 particles (70 um, 110 um). The investigation and analysis of the microstructure and arc erosion mechanism show uniform distribution of fine TiB2 particles in the copper matrix can significantly improve the viscosity of the molten pool and decrease the splashing of molten Cu.

A Study on the Detachment Characteristics of the Tramwave Catenary-Free Electrification System for Urban Traffic

The tramwave catenary-free system (TCS)—a novel type of electrified transit system for urban railways—receives traction energy from a flexible ground-embedded ferromagnetic strip, which is energized only if a corresponding segment is located underneath the vehicle body. The current collector in the TCS is equipped with an “I-shaped” permanent magnet combination that produces a lifting force on the flexible ferromagnetic strips with octopus-shaped copper sheets located on the surface of the strips underneath the ground. The vehicle’s high-voltage circuit conducts when an electrical contact is maintained by the attractive force of the permanent magnet combination mounted inside the magnetic current collector. However, it has recently been observed that due to the dynamic processes during the electrical contact a severe electrochemical corrosion may occur on the surface of the octopus-shaped copper sheets, which can jeopardize the safe operation of the whole electrified transit system of trams. In order to identify the origins of this electrochemical corrosion, the dynamic characteristics of the TCS have been evaluated with particular attention paid to the impact of eddy currents on the attractive force of the permanent magnet combination under variable operational velocities of vehicles. Based on the dynamic characteristics of TCS, the arc erosion process on the surface of the copper sheet has been reproduced using an arc-discharge experimental platform and the causes of electrochemical corrosion in the TCS have been found. The damage development trends—under increasing speeds of trams—evaluated by the dynamic model of the TCS are consistent with the statistical data for practical damage situations.

Arc erosion behavior and mechanism of Ag/Ti3SiC2 cathodes in different atmospheres

Novel Ag matrix electrical contacts, which are environment-friendly, are required to operate under complex service conditions and harsh environments. Therefore, it becomes necessary to urgently study their arc erosion properties in different atmospheres. Herein, Ag/Ti3SiC2 composite samples were fabricated by hot-pressing sintering, and the material's relative density, electrical resistivity, thermal conductivity, Brinell hardness, and flexural strength were measured. Moreover, the arc erosion behaviors of Ag/Ti3SiC2 cathodes in sulfur hexafluoride, nitrogen, and oxygen environments were investigated at 3 kV and 6 kV, and the mass loss, arc current, and discharge duration of the Ag/Ti3SiC2 cathodes in the 3 atm were recorded. The surface morphology and composition of the Ag/Ti3SiC2 cathodes were examined after arc erosion. In this study, the arc energy and mass loss had the highest values in oxygen, followed by nitrogen and sulfur hexafluoride. Following the same trend of operating atmospheres, the erosion-region shape gradually changed from circular to irregular. By means of the Raman spectra, there was no composition change can be detected on the cathode in sulfur hexafluoride, TiNx was detected on the cathode in nitrogen, Ag2O, TiO2 and SiO2 were found on the cathode in oxygen. The resistance of the cathode material to arc erosion deteriorated gradually in the sulfur hexafluoride, nitrogen, and oxygen environments. Importantly, the arc erosion mechanism of the Ag/Ti3SiC2 cathodes in different atmospheres is also proposed in this study. This research can provide a reference for the applications of environmentally friendly Ag matrix electrical contact materials in different atmospheres.

Electrical contact performance of various electro-deposited graphene reinforced silver-based nanocomposites

Abstract Silver and silver(Ag)-graphene(Gr) nanocomposite coatings were prepared via direct current, pulse current and pulse reverse current on copper electrical contacts for evaluating electrical contact performance. The effects of the addition of Gr and current types on microstructure, crystallographic orientation, mechanical properties and electrical contact performance were investigataed via a scanning electron microscope, an X-Ray diffractometer, microhardness test device and an electrical contact test device, respectively. The addition of Gr changed the Ag surface morphology and decreased grain sizes. Moreover, the addition of Gr significantly improved arc erosion resistivity and decreased the average working temperature during the contact test. In addition, pulse current and pulse reverse current provided a significant improvement in microhardness and electrical contact erosion resistance owing to increased embedded graphene amounts in silver layers.

The vacuum breakdown properties and arc erosion behaviors of CuTiW alloys

Cu-Ti alloy ingots were firstly prepared by the induction melting furnace at an argon atmosphere, and CuTiW alloys were fabricated by Cu-Ti alloys infiltrating W skeletons. The effects of Ti contents on the microstructure and properties of CuW alloys were studied. The results show that Ti element can diffuse into W skeletons during infiltration, and the Cu/W interface achieves a good metallurgical bonding. The electric conductivity and hardness of CuTiW alloys is improved after the solution and aging treatment due to the Cu3Ti particles precipitated in Cu matrix. The resistance to arc erosion is improved by the addition of Ti, the arc erosion area is increased and the erosion craters are dispersed effectively, and the breakdown pits hardly appear at the Cu/W interface. Compared with CuW alloy, the Cu-1.5 wt%TiW alloy exhibits the excellent electrical breakdown properties, the breakdown strength is increased by 54%, the chopping current is decreased by 19.3%, and the arc life-span is increased by 46.2%, respectively.

ON-State Contact Resistance and Arc-Less Commutation Characteristics of Cu-W Clad Contact Materials in a Hybrid DC Switch

Hybrid dc switches have better performance with regard to energy conservation and less arc erosion than conventional semiconductor switches and mechanical switches. A novel hybrid dc switch based on a SiC-MOSFET is developed, and it accomplishes arc-less commutation if the current is below a threshold value, which is mainly determined by the boiling voltage of its contact material. However, as it is difficult for common contact materials to have both a low ON-state contact resistance and high boiling voltage, optimization of the contact materials is necessary to further decrease the ON-state contact resistance and improve the arc-less commutation characteristics of hybrid dc switches. New-type Cu-W clad contacts are proposed in this article by brazing tungsten top layers on copper bulks. The performance of the Cu-W clad contacts with the tungsten top layers of different thickness is evaluated by comparing their ON-state contact resistance and the threshold current of arc-less commutation with those of copper contacts and tungsten contacts under dc current ranging from 100 to 400 A. The results of the experiments show that the Cu-W clad contacts with the tungsten top layers of 1 mm thickness are the most suitable for arc-less hybrid dc switches because of their low ON-state contact resistance and largest threshold current of arc-less commutation.

Effects of different atmospheres on the arc erosion behaviors of Ti3SiC2 cathodes

The effects of ambient atmospheres on the arc erosion behaviors of Ti3SiC2 cathodes were investigated at 5.5 kV in argon, nitrogen, air, and oxygen. The mass loss of the cathodes increased in the order of argon, nitrogen, air, and oxygen and the morphologies were measured by 3D laser scanning confocal microscope with a gradual blooming phenomenon. Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to detect the components of erosion regions. The erosion-chemical products mainly consisted of TiNx in nitrogen, TiNx, TiO2 and SiO2 in air, TiO2 and SiO2 in oxygen. The arc energy was responsible for the arc erosion characteristics in different atmospheres.

Investigation of Arc Erosion Mechanism for Tin Dioxide-Reinforced Silver-Based Electrical Contact Material Under Direct Current

To get an in-depth insight into the arc erosion mechanism for tin dioxide-reinforced silver-based (Ag-SnO2) contact material, the contact pairs made of Ag-4wt%SnO2 contact material were, respectively, performed for 20,000 switching operations under the direct currents of 19 A and 29 A and the voltage of 12 V, together with the electrode gap of 4 mm. The eroded surfaces and cross-sectional morphologies and the chemical compositions were characterized by scanning electron microscopy equipped with an energy dispersive spectrometer (EDS). The results show that there is a deep erosion pit at the cathode and an apparent protrusion at the anode, suggesting that a serious material transfer generates from cathode to anode. The EDS results show that the Sn contents at the protrusion and at the region around the crater are below 0.75 wt.% and 4 wt.%, respectively. This reveals that SnO2 undergoes severe evaporation during electrical contact testing. Moreover, arc stability decreases with increasing the load current, and the Ag-SnO2 contact material has larger arc power (make arc: 68.2 J/s; break arc: 58.53 J/s at 29 A) as compared to Ag-TiB2 contact material (make arc: 62.85 J/s; break arc: 50.01 J/s at 29 A). As a result, it is thought that SnO2 evaporation reduces Ag dissipation, thus shortening the lasting time of the make arc. However, the emission current is increased owing to the low work function of SnO2, which further promotes the improvement in the density of the charged particles, thereby enhancing the arc power. Additionally, the large density of charged particles can sustain arc burning for a longer time, resulting in an extended break arc duration.

The formation of the delamination wear of the pure carbon strip and its influence on the friction and wear properties of the pantograph and catenary system

Delamination wear is one of main wear mechanisms of carbon strip of the pantograph-catenary system in the high-speed sliding friction with electric current. In this work, a series of experiments were carried out to simulate the real operating conditions and explore the causes, forming and expanding mechanism of the delamination wear utilizing a ring-on-block wear tester, under high-speed of 350 km/h, strong electric current of 250A and heavy normal loads. Meanwhile, the arc discharge and interface temperature were investigated to clarify the friction and wear mechanisms. The experimental results indicate that the delamination wear of the carbon strip forms expands based on the severe arc erosion, which reveals that arc discharge is a main factor causes the delamination wear. Moreover, the SEM images and EDX analysis show that the plowing wear and copper transfer are the main wear mechanisms of the contact wire, especially, the copper transfer from the contact wire increases suddenly when the delamination wear occurs.

Anisotropic arc erosion resistance of Ag/Ti3AlC2 composites induced by the alignment of Ti3AlC2

Ag/Ti3AlC2 composites prepared by equal channel angular pressing (ECAP) exhibit preferential alignment of Ti3AlC2. Arc erosion behaviors of the Ag/Ti3AlC2 with the alignment of Ti3AlC2 particles parallel (ECAPed//) and perpendicular (ECAPed⊥) to contact surface were investigated. The ECAPed// sample shows superior arc erosion resistance to the ECAPed⊥ one according to the results on surface and cross section examinations, and mass, area and thickness losses. The mechanisms responsible for arc erosion behaviors are discussed in terms of thermodynamic calculations and lattice anisotropic considerations on the oxidation process of Ti3AlC2. The present work provides practical guidance in designing high-performance Ag/MAX electrical contacts.

Microstructure and properties of W-25 wt% Cu composites reinforced with tungsten carbide produced by an in situ reaction

W–Cu composites that are strengthened with tungsten carbide ceramic particles have been proposed thanks to their high melting point, high hardness and excellent high-temperature mechanical properties. In this paper, tungsten carbide-reinforced W-25 wt% Cu composites were fabricated via an in situ synthesis technique that used mixed tungsten, copper and graphite powders. The impact of the graphite content on the microstructure and properties of the W–Cu composite was investigated. The results showed that tungsten carbide phases formed through the carbonization reaction of tungsten and graphite at high temperature. With the generation of tungsten carbide phases, the hardness, vacuum arc erosion resistance, high-temperature strength and wear resistance of the W–Cu composites were improved. The improvement was very significant for the W–Cu composites with an increase in the graphite content. However, the electrical conductivity was slightly sacrificed for the W–Cu composites. Moreover, the effects of the graphite on the comprehensive properties were evaluated and compared with those of reinforced with CNTs. Based on the laboratory properties and preparation cost of W–Cu composites, graphite can be used for the industrial fabrication of in situ self-generated tungsten carbide-reinforced W–Cu composites.

Electrical contact performance of various electro-deposited graphene reinforced silver-based nanocomposites

Abstract Silver and silver(Ag)-graphene(Gr) nanocomposite coatings were prepared via direct current, pulse current and pulse reverse current on copper electrical contacts for evaluating electrical contact performance. The effects of the addition of Gr and current types on microstructure, crystallographic orientation, mechanical properties and electrical contact performance were investigataed via a scanning electron microscope, an X-Ray diffractometer, microhardness test device and an electrical contact test device, respectively. The addition of Gr changed the Ag surface morphology and decreased grain sizes. Moreover, the addition of Gr significantly improved arc erosion resistivity and decreased the average working temperature during the contact test. In addition, pulse current and pulse reverse current provided a significant improvement in microhardness and electrical contact erosion resistance owing to increased embedded graphene amounts in silver layers.

Arc-Erosion Behavior of W/Zr/Cu Electrical Contact Materials Prepared by Functionally Graded Composite Technique

In this paper, mono-layered and functionally graded composites (FGCs) of W, Zr and Cu were prepared through powder metallurgy. Zirconium was used to investigate the possible improvement in arc erosion properties and the underlying mechanisms. The weight loss and the surface morphology of composites were analyzed after 30 vacuum arc discharges. The results showed that the weight loss due to arc erosion was decreased by adding Zr to the functionally graded composite. Compared with mono-layered composites without any additives, the surface morphology of four-layered FGCs containing zirconium and high amounts of Cu particles in the successive layers, showed a homogeneous erosion behavior and the heat concentration and erosion of the surface contacts had been prevented to a great extent. Moreover, due to the higher melting point of Zr than Cu and its smaller work function compared to W and Cu, a substantial part of the arc power was consumed by zirconium leading to a significant reduction of the slight splash of molten copper and the W/Cu contacts.

Effect of Ni addition on the arc-erosion behavior of Ag-4 wt.%SnO2 electrical contact material

To disclose the effect of Ni addition on the arc-erosion behavior of Ag-4 wt.%SnO2 contact material, the Ag-4 wt.%SnO2 contact materials with and without 4 wt%Ni were comparatively studied. The sintered materials were examined by scanning electron microscopy and transmission electron microscopy. The electrical contact tests were performed for different operations on an electrical contact testing system. The eroded morphology evolution and ingredients of the electrical contact surface under the action of arc were characterized, and the mass loss and welding behavior were studied as well. The results show that the Ag-4 wt.%SnO2 contact material has large break-arc-energy, which aggravates the SnO2 evaporation or decomposition. The reduced SnO2 content further decreases the arc erosion resistance and, in turn, causes much serious arc erosion, thereby resulting in larger mass loss and serious welding. However, for the Ag-4 wt.%SnO2-4 wt.%Ni contact material, Ni addition reduces the evaporation and decomposition of SnO2 due to its high melting point and poor thermal conductivity. Additionally, the reiterative dissolution and precipitation of Ag and Ni under the action of arc lead to the formation of fine precipitation phase, which is beneficial for the arc dispersion and generation of stable arc. As a consequence, the evaporation, splash, mass loss and welding are decreased, and the arc erosion resistance is significantly improved.

Electrical wear of TiB2 particle-reinforced Cu and Cu–Cr composites prepared by vacuum arc melting

In this paper, TiB2 particle-reinforced Cu and Cu–Cr composites were prepared by the vacuum arc melting technique. The tensile strength, electrical conductivity and wear properties of the composites were tested. The microstructure and wear morphology of the composites were characterized by SEM. The results showed that microscale TiB2 particles were dispersed uniformly in copper matrix, and the interface between the TiB2 particles and matrix was clean and well bonded. Nanoscale Cr particles were dispersed in the copper matrix. The friction coefficient and wear rate of the composites increased with increasing current. The dual-scale TiB2/Cu–Cr composites with nanoscale Cr particles and microscale TiB2 particles possessed a high strength and hardness, that was conducive to improving the wear resistance. Compared with the wear rate for composites prepared with powder metallurgy, when the current was 50 A, the wear rate of TiB2 particle-reinforced Cu and Cu–Cr composites prepared by vacuum arc melting decreased by 9.3% and 55.3%, respectively. The Cr particles strengthened the copper matrix and the TiB2 particles supported the friction process. The synergistic effect improved electrical wear resistance of the TiB2/Cu–Cr composite. Microstructural observations revealed that the main wear mechanisms of the composites were adhesive wear, abrasive wear and arc erosion.