Achieving stable superlubricity in plain element bearings would considerably help to increase the energy efficiency in technical applications in a simple and cost-efficient way. For this purpose, within the Fraunhofer SupraSlide project using a ball-on-three-pin tribometer, we have identified several combinations of silicon-based ceramics, diamond-like carbon coatings and water-based lubricants (such as glycerol and polyethylene glycol) that are superlubric over a wide range of operation conditions. The mechanisms underlying superlubricity are diverse and depend on the specific system.

In this contribution, I will give an overview of different superlubricity mechanisms that we have identified so far by means of atomistic simulations and that can be categorized into two classes. The first class is based on the formation of amorphous carbon tribofilms. This can be achieved by coating both surfaces with diamond-like carbon, by carbon transfer film formation if only one of the surfaces is coated, or by the tribochemical decomposition of carbon-containing lubricant molecules. The second class of mechanisms relies on the presence of a low-viscosity lubricant that separates the surfaces in contact and is particularly relevant to achieve superlubricity with silicon-based ceramics in the absence of carbon.