Electrical Contact Applications Research Articles

Current-carrying low friction of hydrogenated amorphous carbon film

Hydrogenated amorphous carbon (a-C:H) films, which equip excellent low friction performance but insulated, are naturally excluded from sliding electrical contact applications. In this work, we achieved current-carrying low friction of a-C:H film by utilizing a triboelectric triggered ignition effect. Protective resistors were introduced in the circuit during run-in for effectively alleviating undesired arc ablation. A T-shape crystalline structure of graphite was observed in the wear track by transmission electron microscopy. The parallel-aligned graphite at the top surface induced low friction, while the vertical-aligned graphite in the interior formed efficient electron transmission channels. This study expands the selection range of current-carrying friction films and provides a novel insight for the design and regulation of current-carrying friction films.

Synergistic-strengthening strategy induce excellent electrical and mechanical properties in Cu/AlCrCuFeNi2.5 composites

A novel high-strength conductive Cu-based composite, utilizing AlCrCuFeNi2.5 (Ni2.5) high-entropy alloy particles as the reinforcing phase, is synthesized through a combination of ball milling and spark plasma sintering processes. The mechanical and electrical properties of the composites are optimized by adjusting the composition. Under the synergistic effect of multiple strengthening mechanisms, the fabricated Cu-20 wt% Ni2.5 composites achieve an exceptional compressive strength of 920 MPa while maintaining an electrical conductivity of 44.3 % IACS (International Standard Copper Standard). The establishment of robust interface bonding between Ni2.5 reinforcement and Cu matrix stands as a pivotal assurance for the holistic performance of composites. Ni2.5 HEA is distinguished by good plasticity and high strength compared with traditional brittle reinforcements. An insight into the differences brought about by the distinctive dual-phase structure in terms of interfacial bonding, crack propagation, and performance is provided. It paves the way for selecting and projecting the composites for electrical contact applications, ushering in a realm of fresh possibilities.

Tunable amorphous carbon films formed on ultralow wear, Pt–Au alloys

The mechanocatalytic formation of carbonaceous films at the interface between sliding metallic contacts is simultaneously advantageous for reducing friction and adhesion in several tribological applications and detrimental for electrical contacts as they can induce device failure by increasing the contact resistance. Yet, remarkably little is still known about the chemistry, structural and mechanical properties, and tunability of these interfacial layers. In this study, we performed contact pressure-dependent tribological experiments in dry nitrogen containing trace organics on four, nanocrystalline Pt–Au alloys ([Au] from 0 at.% to 10 at.%) – a promising class of alloys for ultralow wear and electrical contact applications. The ex-situ, multi-technique characterization results did not only provide insights into the chemical nature and mechanical behavior of the mechanocatalytic, carbon-rich films formed on Pt–Au surfaces, but also revealed the interplay between catalytic and mechanochemical tribofilm formation controlled by the composition-dependent electronic structure of the Pt–Au substrate and the applied contact pressure. The results of this work provide guidelines for tailoring nanocrystalline alloys to control their mechanocatalytic activity on the basis of variations of the alloy mechanical properties and element's electronic structure with the alloy stoichiometry.

Graphene-Enhanced CuW Composites for High-Voltage Circuit Breaker Electrical Contacts

To address the issue of over-standard short-circuit currents in a power system, it is imperative to enhance the comprehensive performance of the electrical contacts, which serve as the lynchpin of circuit breakers, so as to improve the breaking capacity of high-voltage circuit breakers. Graphene, as the most prominent two-dimensional carbon material in recent years, has garnered widespread applications across various fields. In this study, graphene-enhanced CuW composites for high-voltage circuit breaker electrical contacts were prepared innovatively using integrated vacuum infiltration technology. The innovative graphene-enhanced CuW composites significantly improved the mechanical, electrical, and ablation resistance properties, and have been successfully applied in the 252 kV/63 kA high-voltage SF6 circuit breakers, achieving 20 times effective consecutive full-capacity short-circuit current breaking. It provides a new route for the development and application of high-performance CuW electrical contacts. Looking ahead, it is planned to extend their application to higher voltage grade high-voltage circuit breakers.

Low friction coefficient bioinspired copper/graphene nanolaminates with high content graphene

Graphene is widely used in metal matrix composites (MMC) to improve the tribological properties of metal due to its special lamellar structure and excellent tribological properties. However, because the aggregation of graphene, it is difficult to increase the content of graphene in metal materials, which seriously hinders the further optimization of friction coefficient. In this paper, we report a bioinspired strategy to fabricate nacre-like copper/graphene nanolaminates through chemical intercalation of copper precursor into the interlayer space of expandable graphite and subsequent reduction. The regular parallel arrangement of graphene can greatly improve the agglomeration phenomenon and the aspect ratio of graphene, which harden the copper matrix by effectively restricting the motion of dislocation and also form continuous lubricating film on the surface. A low dry sliding friction coefficient 0.13 is thus obtained among copper-based composites without severely deteriorating the electrical properties, providing new prospect in sliding electrical contact applications.

Brush Plating of Ag-Bi Coatings from a Cyanide-Free Solution

Ag-Bi coatings were synthesized on copper substrate using brush plating with a cyanide-free electroplating solution for electrical contact applications. Phase constituents, surface morphology, and microhardness of the deposited coatings were characterized. It is found that grain refinement into the nanosized range can be observed for the Ag-Bi coatings with dense and compact microstructure. The electroplated Ag-Bi alloy displayed an apparent hardness increase compared with the pure silver coating. Ag-Bi alloy coatings show promise in the field of electrical contact components used in the electrical power industry.

Progress in the preparation and device research of two-dimensional metallic transition metal dichalcogenides for electrical contact applications

Progress in the preparation and device research of two-dimensional metallic transition metal dichalcogenides for electrical contact applications

Optimized strength and conductivity of multi-scale copper alloy/metallic glass composites tuned by a one-step spark plasma sintering (SPS) process

A superiority in interfacial bonding is favorable to fabricate high-strength conductive composites for electrical contact applications. In the present work, high strength and high conductivity multi-scale metallic glass composites (including micron-scale CuZrAl metallic glass reinforcement, hundred-nanometer-scale CuCrZr crystalline grain matrix, and nano-scale precipitated phase) were fabricated by a one-step spark plasma sintering (SPS). The strength and conductivity of the bulk copper matrix metallic glass composites (BCMGCs) were enhanced simultaneously with the increase in the sintering pressure of the SPS. The excellent performance is attributed to the improved interfacial bonding between the metallic glass reinforcement and the copper alloy matrix due to the high pressure assisted by temperature and pulsed current. In particular, the precipitation of nanoprecipitates at the interface further reduces the interfacial resistance and improves the mechanical properties of the composites. This work broadens the horizon for the selection and optimization of reinforcements and manufacturing processes for high-performance electrical contact materials (ECMs).

Phase-transforming Ag-NiTi 3-D interpenetrating-phase composite with high recoverable strain, strength and electrical conductivity

It is of particular interest to achieve high elastic recoverable strain in the electrical contact materials while maintaining good electrical conductivity and decent tensile strength. It remains a challenge, especially for bulk-sized metallic materials, as the electrical conductivity and elastic strain limit (or tensile strength) are often mutually exclusive. Here, we present a material design strategy for overcoming this conflict by developing a Ag-NiTi composite with an interpenetrating-phase architecture via infiltrating Ag melt into the partially sintered porous NiTi scaffold. The composite exhibits a good combination of properties with high electrical conductivity comparable to metals, large elastic recoverable strain superior to most of bulk-sized conductive metals as well as higher tensile strength than most of alloys/composites based on silver and other noble metals. This new finding demonstrates that the interpenetrating-phase architecture design is promising for developing new materials for electrical contact application.

Investigation of the Microstructure and Properties of Aluminum–Copper Compounds Fabricated by the High-Pressure Die Casting Process

The material combination of aluminum and copper is increasingly coming into focus, especially for electrical contact applications. Investigations of different casting processes show that a significant influence for the formation of a material bond is the thermal impact. For high-pressure die casting (HPDC) processes, the impact is quite low, e.g., due to short cycle times. Despite the high efficiency of this technology, currently there are hardly any investigations in this respect. So, the technology was used in this study to produce aluminum–copper compounds and analyze interfacial layers by means of SEM images and EDX measurements. Furthermore, the mechanical and electrical properties of the compounds were determined by means of tensile shear tests and measurements of the electrical conductivity. By modifying specimen geometry, the thermal impact could be increased and, thus, enhanced compound properties were achieved. Overall, compounds of sufficiently high mechanical strength, as well as electrical conductivity, could be produced by HPDC processes, demonstrating the high technical and economic potential of this casting technique.

Graphene and its derivative reinforced tungsten–copper composites for electrical contact applications: A review

This review summarizes the advancement on sintered composites based on tungsten–copper (W–Cu) reinforced with graphene (Gr) or its derivative such as reduced Gr oxide (rGO) for use as electrical contacts applied in switching devices. Main synthesis approaches for preparing Gr or rGO reinforced W–Cu composite powders and their consolidations by using various powder metallurgy techniques are presented. The nature of the initial materials, synthesis conditions, processing parameters, and the relevant findings are disclosed and discussed. The improvement in microstructure and technical characteristics like density, electrical conductivity, hardness, coefficient of friction, wear rate, and arc ablation behavior of W–Cu–Gr/rGO composites are highlighted comparatively with that of unreinforced composites. This review reveals an insight into a novel class of composites as candidates for electrical contact applications.

The wear resistance of Al–Si–Re alloys for electrical contact applications

We prepared aluminum–silicon–rare earth (Al–Si–Re) elements alloys for electrical contact applications. Three Si weight percentages (wt.%) — 10%, 20% and 30% — were used, and rare earth (Re) elements were kept at 0.35 wt.%. The spraying forming process was adopted, and high-pressure hot isostatic pressing (HIP) was conducted to obtain the bulk materials from the as-deposited billets. The electrical conductivity of alloys with 10% and 20% Si reached 40% International Annealed Copper Standard (IACS). The hardness of Al–Si alloys significantly increased with Si content and HIP processing times. The hardness of alloy with 30% Si reached [Formula: see text]90 HV. Meanwhile, HIP reduced weight loss in the wear resistance by reducing the microcracks and materials removal. The current study proposes an approach to manufacture Al–Si alloys with high electrical conductivity and high wear resistance.

Grease-lubricated tribological contacts – Influence of graphite, graphene oxide and reduced graphene oxide as lubricating additives in lithium complex (LiX)- and polypropylene (PP)-thickened greases

Two types of thickener systems, lithium complex (LiX) and polypropylene (PP), were chosen to evaluate graphite, graphene oxide (GO) and reduced graphene oxide (rGO) as grease additives at a concentration of 0.1 wt%. To enhance the additive dispersibility, a mixture of polyalphaolefin oil (PAO) and oil soluble synthetic polyalkylene glycol (OSP-68) was used as base oil. The greases were evaluated in i) silver-coated copper contacts simulating high-load electrical contact applications subjected to fretting and ii) a steel/steel 4-ball wear test equipment. The additives showed no positive effect on friction and wear, neither in fretting nor in 4-ball tests. However, there is a statistically significant difference in wear scar diameter on the 4-ball steel contacts between the two thickener types, LiX and PP. Thus, the PP-grease lubricated steel contacts showed more wear and more tribofilms of iron oxide and grease constituents, indicating more metal-to-metal contact. Hence, the thickener type has a larger impact on the lubricating performance of the grease than do the graphite, GO and rGO additions. The results demonstrate that the addition of graphene-based materials to improve greases is not straightforward. Rather, the grease/graphene-based additive system is complex and many parameters influence the friction and wear results. Hence, more work is needed to obtain a better understanding and possibly better lubricating effects from the graphene-based additives.

Modulating the thermal and structural stability of gallenene via variation of atomistic thickness.

Using ab initio molecular dynamics, we show that a recently discovered form of 2D Ga—gallenene—exhibits highly variable thickness dependent properties. Here, 2D Ga of four, five and six atomic layers thick are found to be thermally stable to 457 K, 350 K and 433 K, respectively; all well above that of bulk Ga. Analysis of the liquid structure of 2D Ga shows a thickness dependent ordering both parallel and perpendicular to the Ga/vacuum interface. Furthermore, ground state optimisations of 2D Ga to 12 atomic layers thick shows a return to a bulk-like bonding structure at 10 atoms thick, therefore we anticipate that up to this thickness 2D Ga structures will each exhibit novel properties as discrete 2D materials. Gallenene has exciting potential applications in plasmonics, sensors and electrical contacts however, for the potential of 2D Ga to be fully realised an in depth understanding of its thickness dependent properties is required.

Electrical Conductivity of Spark Plasma Sintered W-Cu and Mo-Cu Composites for Electrical Contact Applications

Tungsten copper and molybdenum copper composites, with weight percent copper in the range of 20% - 40%, have been produced using the spark plasma sintering (SPS) technique. Other specimens having similar compositions were also developed using the conventional techniques of Liquid Phase Sintering (LPS) and Infiltration. Electrical conductivity measurements showed that the specimens produced by the SPS process had substantially higher levels of electrical conductivity than those produced by the other methods. Relative density measurements showed that the SPS specimens achieved very high densification, with relative densities in the range of 99.1% - 100%. On the other hand, the specimens produced by LPS and infiltration had relative densities in the range of 88% - 92% and 96% - 98% respectively. The superior conductivity of the SPS specimens has been attributed to the virtually full densification achieved by the process. The effect of porosity on electrical conductivity has been discussed and three standard models were assessed using results from porous sintered skeletons of pure tungsten and pure molybdenum.

Study of mechanical and tribological properties of hybrid copper metal matrix composite reinforced with graphite and SiC

As application of composite material is increasing, hybrid metal matrix composite is getting popular day by day. In this study, an effort is made to investigate the effect of graphite and other reinforcement materials (B 4 C, Al 2 O 3 , and SiC) in copper (Cu) metal matrix, fabricated by using powder metallurgy method. The effect of sintering temperatures in the range of 900–950 °C on mechanical and tribological properties at 700 MPa compacting pressure is studied. Initially the most wear resistive reinforcement SiC is chosen because of less wear rate of 3.226 × 10 −4 mm 3 /N-m at 5% of wt. percentage. Graphite (Gr) reinforcement of 1.5% to 3.5% and SiC reinforcement of 5% are added in the copper matrix. Composite containing SiC reinforcement will help in improving hardness as well as wear resistance properties, whereas Gr reinforcement will improve frictional resistance property, as it acts like a lubricating film and has low coefficient of friction. The experimental results revealed that hybrid Cu composite at 3.5% of graphite and 5% of SiC reinforcement has minimum density of 6.27 g/cm 3 at a sintering temperature of 900 °C. Also at the same wt. % it has lowest wear rate of 1.2 × 10 −4 mm 3 /N-m and the lowest coefficient of friction of 0.2 at sintering temperature of 950 °C. The hybrid composite at 5% of SiC and 1.5% of Gr at 950 °C have the highest hardness of 89 HRC and highest compressive strength of 567 MPa. That hybrid composite is used in contact bushes, bearing materials and other electrical contact applications.

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.

Investigation on Graphene-Coated Silver-Palladium Microelectrical Contact and Effect of Coating Thickness

This article investigates silver-palladium (AgPd) microelectrical contact coated with graphene (Gr). An analysis is carried out for 2-D, circle-rectangle microelectrical contact using COMSOL multiphysics finite element analysis (FEA) simulation software tool. Under applied force between 6 and $15~\mu \text{N}$ , mechanical performance parameters such as contact radius, depth of penetration, and contact pressure are obtained for AgPd uncoated microelectrical contact. The results are validated with the Hertz contact model. The analysis is also carried out for the AgPd microelectrical contact coated with graphene (Gr). The Gr coating thickness is varied between 5 and 10 nm, and better mechanical performance is obtained for lesser coating thickness. This result shows that Gr can be used as a coating and lubricant on AgPd for electrical contact applications.

Effect of Transition Metals Oxides on the Physical and Mechanical Properties of Sintered Tungsten Heavy Alloys

The addition of transition element oxides to tungsten heavy alloys (WHAs) fabricated by powder metallurgy technique provides new materials with higher density and electrical conductivity, which may be adequate in some applications such as kinetic energy penetrators. Additionally, materials with higher electrical conductivity are required for electrical contact applications such as electrical discharge machining (EDM) electrode materials. WHAs were fabricated by compacting its mixed constituents followed by sintering. Ni, Co and Fe are used as binding phases of the tungsten particles and oxides of Zr, Ti and Y are used as oxide dispersing strengthening (ODS) agents of the sintered materials. The results show that all of the chosen factors (i.e., pressure of compaction process, temperature of sintering, type of binding material and type of oxide) have clear effects on all properties of ODS tungsten heavy alloy specimens. The density and electrical conductivity increase with the increase in sintering temperature. Hardness and compression strength were also measured to evaluate the mechanical properties of sintered samples.

Synthesis and Tribological Characterization of Copper Based Composites Containing Carbide

Keeping in view the importance of the Cu based composites in sliding electric contact applications, the aim of the study is synthesise copper-chromium alloy based composites containing different wt. % of TiC by using a cost effective stir casting technique and to compare their mechanical and tribological behaviour. The study also proposes to analyse the friction and wear behaviour of the formed composites under the sliding speed of 1m/s and load varied 5 N, 10 N, 15 N and 20 N. The hardness of the composite Cu-1wt%Cr-1wt%TiC and Cu-1wt%Cr-2wt%TiC has been found to increase slightly when compared with Cu-Cr alloy and as received Cu. The wear rate was found to show linear trend with increasing normal load following the Archard law. However, composites were found to show low wear as compared to that observed in pure copper. This might be due to high hardness of the composite, the compact transfer layer of wear debris and due to presence of hard TiC particles whicg results in a lower real area of contact which further causes lower wear. There was found no cracks in the composite. The addition of chromium was found to increase the wettability and mechanical properties. The composite hardness and strength was found to increase with addition of TiC and chromium element in the matrix phase up to certain content.