Electrical contacts and tribology are based on solid surface which is very complex situation. Electric current flow through small true contact area of the solid surface, and tribological phenomena occurs at the same area. In this paper, contact resistance properties are described in detail together with friction coefficient. Electrical contacts are related closely to the tribology of complex phenomena.

The wear behaviors of five types of materials used for electrical contact - gold, silver, copper, graphite, and tin - are reviewed, with a focus on the influences of oxygen and water vapor. Gold, silver, and copper demonstrate distinct wear patterns determined by their respective reactivity with atmospheric gases. Among them, the wear of gold remains unaffected by the presence of oxygen and water vapor. In contrast, the wear of graphite significantly decreases when water vapor is present in air. Particularly, experiments that independently change sliding speed and non-friction time indicate the importance of the actual friction time at the real contact area. Conversely, the wear of tin substantially increases when oxygen and water vapor are blown to the friction interface, leading to the growth of transfer particles and the subsequent production of large wear particles.

The identification and evaluation of tribological phenomena involving electrical contact is important for maintaining the performance and extending the lifetime of machine elements that are in contact and friction while electric current is applied to them. Acoustic emission (AE) is a phenomenon in which deformation or fracture of a material releases previously stored strain energy, which propagates inside the material as elastic stress waves (AE waves). AE waves are also generated at a frictional interface in a series of processes from contact with surface asperities to deformation and fracture. AE sensing allows AE waves to be measured as AE signals and analyzed to identify and evaluate various phenomena at the frictional interface. This article provides a wide commentary on the utilization of AE sensing for the identification and evaluation of tribological phenomena involving electrical contact, from the main points to application cases.

Brushes are used in commutator and slip ring systems. In recent years, the reduction of brush wear has become a topic, and efforts to reduce wear have become important. In this paper, we will explain based on the contents of experiments aimed at reducing brush wear.

Overhead contact line-pantograph system is generally used as a current collection technology in electric railways. From the point of view of electric contacts, this system can be regarded as a sliding contact between current collecting materials such as contact wire of overhead contact line and contact strip of pantograph. The main conditions governing current collecting characteristics, such as current, sliding speed and contact force, largely fluctuate, resulting in complex wear of current collecting materials. In this paper, the author introduces some theories that are often used in electric contacts and explains some studies that focus wear mode transition by Joule heat. From the wear test results in low sliding speed condition, it is found that the main factor of electric wear of current collecting materials is not arc discharge but molten bridge. Using the parabolic relationship between electric potential and temperature, a map which shows the transition condition among electric wear modes is proposed. In addition, the author shows an example of temperature analysis result in unsteady state, and prospects the future research in high sliding speed.

Owing to recent home computerization, electrical corrosion of rolling bearings comes to arise in home appliances. In the rolling bearings, since the material of inner ring, outer ring and rolling elements is the same (high carbon-chromium bearing steel), galvanic electrical corrosion does not intend to arise. However, when a large electrical potential of difference worked between inner ring and outer ring and/or axis and housing, electrical discharge intended to happen with smashing through the oil film inside the bearing. If the phenomenon continued a long span of time, the noise and vibration of the bearing increased. This damage is called “electrical corrosion”. This is considered as one of the wear phenomenon. This article describes a formation state and a growth process of ridge mark as a result of electrical corrosion.

The tribological properties of two polymethyl methacrylate (PMMA) copolymers were studied, both of which were specially synthesized by the living-anion polymerization method using highly concentrated methyl methacrylate, lauryl methacrylate and stearyl methacrylate as monomers. Chemical structure of PMMA was identified as block and random copolymers by ¹³C nuclear magnetic resonance, gel permeation chromatography and Fourier transfer infrared analysis. The presence of adsorbed films on iron oxide was confirmed by atomic force microscopy with tapping mode. In addition, the block copolymer was greater film thickness than the random copolymer from the topographic image. From the EHL test, the block copolymer solution formed a thicker oil film, and showed a lower traction coefficient than the random copolymer solution at low speeds. On the other hand, both the polymer solutions showed almost the same coefficient of friction in the ultra-low speed test. In other words, the block copolymer has better traction properties in the partial EHL region due to its better oil film-forming ability than the random copolymer. Furthermore, the partial EHL analysis revealed that the oil film behavior was influenced by the polymer enriched film at the inlet region in the case of the random copolymer and dominated by the viscoelastic properties of the adsorption film in the case of the block copolymer.

ZnDTP is used in lubricating oils as an antioxidant to inhibit oxidation. However, the use of ZnDTP has been discouraged because it contains phosphorus, which has a high environmental burden, and a new multifunctional additive is required. Thus, fullerenes are attracting attention as a new multifunctional additive to replace ZnDTP. If fullerene-added oils are used in actual equipment, it is essential to have an indicator to detect consumption. However, there is no established method for diagnosing the consumption of fullerenes in lubricating oils. Our present work is to develop a degradation diagnostic method for fullerene-added oils, which are expected to be used in the future. We oxidized the fullerene-added oils and investigated the relationship between the UV absorbance characteristics and the color change of the membrane patch. As a result, the UV absorption spectrum decreased, and the color of the membrane patch changed by scavenging radicals. These consequences indicate that the double bond of the fullerenes is cleaved during the radical scavenging and the resulting fullerene reactants are trapped in the membrane filter. Thus, it is suggested that the consumption of fullerenes can be easily detected by observing the change in hue.