The energy transition and the electrification of private transport are making the requirements for the safe and reliable transport of electrical energy even more important for society. A stable power grid requires a high degree of reliability from all components involved. Connections where electrical energy is transferred from one conductor to another are often critical points. Coatings on the individual contact partners have been state of the art for years. The increasing demands and challenges require the use of new materials with which existing equipment can be further developed. The requirements for coatings in the area of current-carrying plug connections in power grids have risen sharply in recent years. Due to the more compact design of devices and increasing power density, the temperatures in use are rising. If a high number of mating cycles is also required, the design and installation challenges are high. Connectors with a high number of mating cycles are currently pre-treated with a contact lubricant to minimise frictional wear during operation.
The contact lubricant must be stable over the long term and temperature-resistant so that the required operating times of several decades in some cases can be achieved. During assembly, care must be taken to dose the contact lubricant precisely so that the contact resistance is only moderately increased, but at the same time the coefficient of friction is reliably reduced. In addition, the materials used usually contain fluorochemicals, which are expensive to procure and problematic to produce and dispose of.
Silver dispersion coatings with embedded dry lubricants are an alternative to the pure silver coatings normally used, which are treated with contact lubricants. The aim of the project was to develop and investigate electroplated silver dispersion coatings with self-lubricating properties. The particles to be deposited were added to the metal matrix electrolyte in the form of powders and kept in suspension by appropriate electrolyte circulation. By selecting the appropriate process and electrolyte parameters, it was possible to control the incorporation of the particles into the coating.
In summary, the results of the project show that all investigated particle types can be incorporated into silver coatings when coating model geometries. The silver-graphite, silver-MoS2 and silver-WS2 systems stand out due to their good tribological properties. Values of around 0.2 are achieved for the average coefficients of friction, which remain stable even after thermal ageing for 2000 h at 180 °C. In addition, the incorporation of dispersoids slows down the drop in hardness as a result of heat treatment compared to pure silver coatings.
These results can also be confirmed in principle on the industrial test specimens. The maximum friction path of a silver dispersion layer up to failure increases by a factor of 3-6 (WS2), 5-10 (MoS2) or 10-18 (graphite) compared to a pure silver layer. However, the values of a silver surface treated with contact lubricant are not yet achieved. This could be the subject of further investigations.
