Abstract
The potential of graphene as a solid lubricant in sliding Ag-based electrical contacts has been investigated. Graphene was easily and quickly deposited by evaporating a few droplets of a commercial graphene solution in air. The addition of graphene reduced the friction coefficient in an Ag/Ag contact with a factor of ~10. The lubricating effect was maintained for more than 150,000 cycles in a pin-on-disk test at 1 N. A reduction in friction coefficient was also observed with other counter surfaces such as steel and W but the life time was strongly dependent on the materials combination. Ag/Ag contacts exhibited a significantly longer life time than steel/Ag and W/Ag contacts. The trend was explained by an increased affinity for metal–carbon bond formation.
Highlights
Electrical contacts are important in modern technology
We have investigated the tribological behavior of these materials combinations with added graphene and characterized the contacts with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS)
The lubricating effect of graphene was evaluated by measurements of friction coefficients of a clean Ag surface and a graphene-modified Ag surface using three different counter materials Ag, steel, and W
Summary
Electrical contacts are important in modern technology. From a materials science point of view, the design of such contacts is a complex problem, in particular for a sliding contact. In a sliding contact application, it is too soft and the friction coefficient between two sliding Ag surfaces is far too high ([1). There is a need to modify the Ag surfaces to reduce the friction coefficient by e.g., adding a surface coating on the Ag contact. One example for such coating is AgI which can be deposited by electrochemical techniques or by exposure to an I2 solution [1,2,3]. Ag versus AgI-coated Ag contacts typically exhibit a friction coefficient of 0.3 but have a limited life time as the AgI coatings have a rather high wear rate [3]. Other methods to produce low friction surfaces on Ag contacts with long lifetimes are needed
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