Electrical Contact Materials Research Articles

Characterization of Nanocrystalline Cu25Mo Electrical Contact Material Synthesized via Ball Milling

Characterization of Nanocrystalline Cu25Mo Electrical Contact Material Synthesized via Ball Milling

Arc erosion behavior and mechanism of Cu/Cr20 electrical contact material

Cu/Cr20 material was prepared by spark plasma sintering. And then the arc-erosion tests of electrical contacts were carried out under the condition of constant current load with JF04C contact material test system. The trend of mass change (loss and transfer) of the Cu/Cr20 contact material was analyzed, when the current is less than 35 A, mass loss of material increases with the increase of current, when the current is 40 A, material is transferred from cathode to anode. The SEM was employed to investigate the surface morphologies of arc-eroded specimens of the Cu/Cr20 electrical contact materials. In accordance with the relevant experimental data, the relationship among arcing time, arc energy, and welding force was analyzed, and there is a linear relationship between the arcing time (t) and arc energy(E) (E=143.9t−158.3). The results indicate that the phenomena of material melting and transfer are caused by DC arc. There are molten pools, pits, porosity, cracks and coral structure distributed on the surface of contacts. And composition segregation phenomenon occurred on the arc erosion layer at the same time. With the increasing of operation times, there is a positive linear correlation between arc energy and the arcing time.

Explosion welding of Al + Cu bimetallic joints for electrical contacts

The manufacture of aluminium + copper electrically conducting bimetallic materials for electrical contacts and adapters by explosion welding was investigated. It is shown that the damping layer can be used efficiently for the protection of the surface of the flyer plate in the manufacture of the M1 + AD1 bimetal. The conditions of explosion welding of the bimetal using an explosive substance consisting of a mixture of porous ammonium nitrate with diesel fuel at a ratio of 96:4 are investigated. The effect of the structure on the physical and mechanical characteristics of the bimetallic material (ultimate tensile strength, shear and bending resistance, specific electrical conductivity) is studied.

Processing and Electrical Properties of Nano-Al<sub>2</sub>O<sub>3</sub>/Cu Composites

Copper matrix composites (CMCs) are widely used in electrical equipment and electrical contact materials due to their excellent electrical properties. Al2O3 powders are widely used as a reinforcing agent to enhance mechanical properties of MMCs. The xAl2O3/Cu (x =0, 0.2, 0.5, 0.7, and 1.0wt. %) composites were prepared via vacuum arc melting method. The mechanical and electrical properties were obtained by measuring the hardness and conductivity. The morphology of copper and Al2O3/Cu composites was characterized by optical microscopy (OM) and scanning electron microscopy (SEM). With the addition of Al2O3 from 0.2 wt. % to 1.0 wt. %, the relative densities of composites decreased from 98.5% to 97.0%. The hardness of the composites increased with increase in the Al2O3 powders content. The hardness of 1.0Al2O3/Cu composites was 57.9 HB, which was higher than that of pure Cu by 18.6%.. With the addition of Al2O3, the IACS% of Al2O3/Cu composites decreased from 88.97 to 86.16.

Effect of grain size on the electrical conductivity of copper–iron alloys

Copper–iron alloys (CFAs) are a much anticipated class of materials for electrical contacts, magnetic recordings, and sensors. In this study, Cu100-xFex alloys (x = 10, 30, or 50, representative of the Fe content in at%) were prepared via gas atomization, followed by sintering and heat treatment in vacuum. The electrical conductivity of the alloys was determined as a function of the grain size. The substitutional solid solution formed between copper and iron during alloy synthesis is decomposed during the subsequent heat treatment, followed by sluggish grain growth in samples of all compositions, but it was highest in the sample consisting of 10 at% of iron. In the samples with the other two compositions, grain growth was very slow and the grain boundaries were pinned by the Fe-rich phase. Bulk samples of all compositions with powder particles measuring ∼24 μm exhibited higher electrical conductivity with longer durations of heat treatment.

High-speed imaging observation on molten bridges of AgNi10 electrical contact material

The electrical contact–high-speed imaging experimental system was developed to investigate the molten bridge phenomena of AgNi10 electrical contact material. The dimension of molten bridges was measured along with the measurement of waveforms in the contact voltage under the load of direct current (DC) 6 V (8–20 A) and breaking speed of 50.0 mm·s−1. A part of the observed results was presented as well as surface morphology of the contacts after electrical contact behavior, which shows some interesting and new phenomena. Molten bridges and arc could exist simultaneously. The stable molten bridge looks like cylindrical shape and then becomes needle tip at its rupture, the diameter and length of molten bridges both increase with the increase in current and the growth gradient of the diameter is larger than that of the length. The morphology and elemental distribution of the contact surface are changed by the behavior of electrical contact.

Low-temperature-cured highly conductive composite of Ag nanowires & polyvinyl alcohol**Project supported by the National Natural Science Foundation of China (Grant No. 61306080), the Natural Science Foundation of Hunan Province, China (Grant No. 2015JJ3143), and the Scientific and Technological Project of Hunan Provincial Development and Reform Commission, China.

Flexible conductive films were fabricated from a low-temperature-cured, highly conductive composite of silver nanowires (as conducting filler) and polyvinyl alcohol (PVA, as binder). Sheet resistance of 0.12 Ω/sq, conductivity of 2.63×104 S/cm, and contact resistance of 1.0 Ω/cm2 were measured in the films, along with excellent resistance to scratching and good flexibility, making them suitable electrical contact materials for flexible optoelectronic devices. Effects of curing temperature, curing duration, film thickness, and nanowire length on the film’s electrical properties were studied. Due to the abundance of hydroxyl groups on its molecular chains, the addition of PVA improves the film’s flexibility and resistance to scratching. Increased nanowire density and nanowire length benefit film conductance. Monte Carlo simulation was used to further explore the impact of these two parameters on the conductivity. It was observed that longer nanowires produce a higher length-ratio of conducting routes in the networks, giving better film conductivity.

In situ formation and doping of Ag/SnO2 electrical contact materials

The Ag/SnO2 electrical contact materials with different doping concentration of Zr and Fe were successfully fabricated through self-assembly precipitation and powder metallurgy method. The microstructures of Ag-SnO2 composite powders and the prepared Ag/SnO2 contact materials were investigated by a Scanning Electron Microscopy (SEM) coupled with EDS and EBSD systems. The results showed that the SnO2 nanoparticles with typical geometric shapes were formed and distributed in Ag matrix. The electrical conductivity of the Ag/SnO2 materials was significantly increased by 16 percent with the doping of 3 wt% ZrO2 in SnO2. The surface morphology of the Ag/SnO2 materials after arc erosion was further characterized. The formation of the Sn(Zr)O2 and Sn(Fe)O2 solid solution in Ag/SnO2 significantly improved the arc dispersion and arc erosion resistance. This work can offer a novel approach to design Ag/SnO2 contact materials for good electrical performances.

Copper-MAX-phase composite coatings obtained by electro-co-deposition: A promising material for electrical contacts

A new and promising composite coating system comprising copper and MAX phase particles (commercial powder consisting of Ti2AlC and Ti3AlC2) was prepared electrochemically using direct current electrodeposition. The MAX phase particles, in micro-scale sizes, were successfully incorporated (up to 3wt%) and well distributed in the copper coating. The change in the coating properties such as hardness, electrical contact resistance as well as crystallographic structure was investigated in layers having thickness values of about 50μm. Furthermore, the behavior of the composite layers under electrical arcing conditions was studied. Beside an increase of the hardness and a slight change in the structure due to particle incorporation, it could be shown that the electrical contact resistance of the composite coatings is similar to the one of pure copper films deposited at the same conditions. An improved behavior under electrical arcing was found for the composite coatings. After the arcing experiments no significant changes of the morphology of the composite coatings were found, whereas, the pure copper layers showed melting and recrystallization. The composite layers are, therefore, a suitable alternative for electrical applications such as electrical switching devices.

Fabrication and Arc-Erosion Behavior of Ag8SnO2 Electrical Contact Materials under Inductive Loads

Fabrication and Arc-Erosion Behavior of Ag8SnO₂ Electrical Contact Materials under Inductive Loads

Preparation of copper–molybdenum nanocrystalline pseudoalloys using a combination of mechanical activation and spark plasma sintering techniques

Nanostructured powders of pseudoalloys of immiscible Cu and Mo metals are prepared by highenergy ball milling (HEBM). Mechanical alloying in an Activator-2S planetary ball mill for 60 min provides a uniform distribution of refractory Mo particles in a moldable Cu matrix on submicron and nanoscopic levels. Nanostructured Cu–Mo powders are consolidated by spark plasma sintering (SPS) in a temperature range of 700–950°C at a pressure of 50 MPa for 10 min. The effect of preparation conditions on the microstructure, crystal structure, and properties (density, hardness, electric resistivity) of the nanostructured Cu–Mo pseudoalloys is studied. It is shown that a combination of HEBM and SPS provides the formation of a high-density (97%) nanostructured consolidated Cu–Mo composite with a hardness of 3.68–3.88 GPa and an electric resistivity of 6.1–6.2 μΩ cm; these parameters made the composite promising for use as an electric-contact material.

A novel preparation of resin-based electrical contact material impregnated with sulfonated graphene

A novel type of resin-based electrical contact material (RECM) was prepared for the first time via the second curing of a sulfonated graphene/waterborne epoxy resin after pore formation.

Formation and effects of CuO nanoparticles on Ag/SnO2 electrical contact materials

The Ag/SnO2 contact materials modified by the in situ formed CuO nanoparticles were prepared through a self-assembly-precipitation method combined with powder metallurgy. The micro morphology and composition proportion of the Ag-CuO composite powders were investigated. The microstructures and physical properties of the prepared Ag-CuO/SnO2 materials were studied. After arc erosion, the surface morphology and element distributions of the Ag-CuO/SnO2 materials were characterized by Scanning Electron Microscopy (SEM) and Electron Probe Microanalysis (EPMA). The results showed that the CuO nanoparticles smaller than 10 nm were formed on the whole surface of Ag powder. The electrical conductivity of the Ag/SnO2 contact materials was significantly increased with the introduction of CuO, and the hardness, however, was slightly decreased, which could improve the workability. The formation of ultrafine CuO nanoparticles significantly improved the arc dispersion and arc erosion resistance of Ag/SnO2 materials. The aggregation of SnO2 particles in the erosion area was effectively suppressed.

Investigation on arc erosion behaviors and mechanism of W70Cu30 electrical contact materials adding graphene

In this work, graphene was chosen to add into W70Cu30 alloys to develop properties of arc erosion. The effect of graphene addition on arc ablation behavior of W70Cu30 contacts was investigated by the measurement of weight-loss and the vacuum electrical breakdown tests. Also, the surface morphology of W70Cu30 contacts was analyzed by using scanning electron microscopy (SEM) after arc breakdown the first and 100 times. The results reveal that addition of graphene can enhance the breakdown strength a lot, which reach up to ∼45.5%, with a maximum value of 8.5 × 106 V/m. Compared with W70Cu30 alloys without any additives, the surface morphology of W70Cu30 alloys with graphene addition have a slight splash of molten copper and a small, flat cathode craters, thus, avoiding the concentration erosion on the surface of contacts. The main ablation mechanisms of W70Cu30 alloys with graphene addition was considered to be electron transition, energy consumption and difference work function of W, Cu, graphene, respectively.

The Effect of Flake Microstructure on the Preparation and Properties of Cu–Graphite Sintered Nanocomposites

A novel powder metallurgy method, based on preparation of powder mixtures of copper with 0.5, 1, 1.5, 2, 2.5, 3, and 5 wt.% of nanographite particles ~50 nm in size, is used to produce Cu-nanographite electrical contact materials with flake microstructure. The dispersion of graphite nanoparticles in the Cu matrix is examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Morphology, particle size, and apparent density of flake powders are investigated. Microstructure, density, electrical conductivity, and hardness are studied for green and sintered samples. The composites reinforced with lower graphite nanoparticles content (0.5 wt.%) exhibit much lower agglomeration content, while the composites reinforced with higher graphite nanoparticles content (5 wt.%) showed higher agglomeration content. It is found out that the electrical conductivity of the sintered Cu-nanographite electrical contact materials decreased from 76.92 to 68.28 IACS by graphite nanoparticle addition. The maximal (~34) and minimal (~20) Brinell hardness is obtained for the monolithic Cu sample and 5 wt.% graphite nanoparticle reinforced Cu electrical contact materials, respectively.

Material transfer behavior of AgTiB2 and AgSnO2 electrical contact materials under different currents

To clarify the effect of the characteristics of strengthening phase on the material transfer behavior of silver base contact materials, the good electrical and thermal-conductive TiB2 ceramic and insulating and poor thermal-conductive SnO2 ceramic were selected as the strengthening phases, and the Ag-4wt.%TiB2 and Ag-4wt.%SnO2 contact materials were prepared with different sized TiB2 and SnO2 powders by powder metallurgy. The electrical contact tests were performed on an electrical contact material testing system at a voltage of 12VDC and a current ranging from 5 A to 24 A. The results show that the material transfer mode is from cathode to anode at small currents for the Ag-4wt.%TiB2 contact material. However, it changes reversely at large currents. For the Ag-4wt.%TiB2 contact materials prepared with 500nm and 60nm TiB2 powders, the critical current at which the material transfer mode changes are 16 A and 24 A, respectively. Nevertheless, the material transfer mode for the Ag-4wt.%SnO2 contact material is always from cathode to anode at 5-24 A. Furthermore, fine strengthening particles are beneficial for less mass loss and relative transfer mass for both Ag base contact materials. The Ag-4wt.%TiB2 contact material presents a lower relative transfer mass than Ag-4wt.%SnO2 contact material.

Thermostability, mechanical and tribological behaviors of polyimide matrix composites interpenetrated with foamed copper

Polyimide matrix composites interpenetrated with foamed copper were prepared via pressure impregnation and vacuum immersion to focus on their thermostability, mechanical and tribological behaviors as sliding electrical contact materials. The results show that the interpenetrating phase composites (IPC) are very heat-resistant and exhibit higher hardness as well as bending strength, when compared with homologous polyimide matrix composites without foamed copper. Sliding electrical contact property of the materials is also remarkably improved, from the point of contact voltage drops. Moreover, it is believed that fatigue wear is the main mechanism involved, along with slight abrasive wear and oxidation wear. The better abrasive resistance of the IPC under different testing conditions was detected, which was mainly attributed to the successful hybrid of foamed copper and polyimide.

Copper matrix composites reinforced by aligned carbon nanotubes: Mechanical and tribological properties

The hardness, strength, and abrasion resistance of copper for electrical contact materials is poor. Thus, we aligned carbon nanotubes in Cu matrix composites through die-stretching for their excellent mechanical properties and abrasion resistance. The Cu matrix composites with varying CNTs volume fraction from 0 to 10vol.% were fabricated under protective atmosphere sintering of a mixture of Cu powders and Ni/Cu coated CNTs. This was followed by forging and die-stretching. The CNTs were uniformly dispersed in the dense composites, and the trend of their alignment along the stretching direction was obvious. The composites were anisotropic, and their mechanical properties and abrasion resistance increased obviously with the addition of CNTs. The 5vol.% CNTs/Cu composite showed the best hardness, tensile strength, and abrasion resistance. The mechanisms underlying the improved mechanical and tribological behavior were evaluated, and this research provides novel ideas and technology for the distribution and directional alignment of CNTs in the matrix.

Effects of Oxide-Modified Spherical ZnO on Electrical Properties of Ag/ZnO Electrical Contact Material

Silver-zinc oxide (Ag/ZnO) electrical contact material is widely used as contacts of the medium duty switching devices. Effects of modified ZnO on properties of Ag/ZnO electrical contact material were investigated in this work. NiO and CuO were introduced to modify spherical ZnO by a chemical solution nano-coating method. Ag/ZnO contacts prepared using the modified spherical ZnO were produced by powder metallurgy (PM) method in a muffle furnace in temperature ranges from 750 to 900 °C. Results show that electrical conductivity, stability of relative density, and Vickers’ hardness of Ag/ZnO electrical contact material can be improved by the addition of NiO because of the formation of NiO solid solution Zn0.2Ni0.8O. The addition of CuO to Ag/ZnO electrical contact material makes arcing energy and mass loss lower. Since this is attractive for a longer service life, using NiO and CuO co-modified ZnO as a second phase may be a promising way to improve properties of Ag/ZnO electrical contact material. Hence, the presented results could also be useful for the design of a new Ag/ZnO electrical contact material.

Anti-Arc Erosion Properties of Ag-La2Sn2O7/SnO2 Contacts

La2Sn2O7/SnO2 composite powder was synthesized by chemical co-precipitation, and Ag-La2Sn2O7/SnO2 electrical contact material was prepared by a powder metallurgy method. Anti-arc erosion properties, mass loss and Vickers hardness of the Ag-La2Sn2O7/SnO2 composite were investigated, and its anti-arc erosion mechanism was discussed. Results show that the welding force of Ag-La2Sn2O7/SnO2 composite is much better than that of Ag-SnO2, because the new phase La2Sn2O7 can increase the viscosity of melt pool and improve wettability between silver and tin oxide to some extent. Meanwhile, Flatter arcing area and “beads-like” particles embedded scatteredly in the surface could decentralize arc energy via “pinning effect”, which decreases temperature rise and weakens the damage of surface structure, and better anti-welding property is obtained. Ag-La2Sn2O7/SnO2 composite could be a leading candidate material for electrical contacts in the future.