Tribological contacts are responsible for about 23% (119 EJ) of the world's energy consumption. In the field of superlubricity, incommensurability between rotating graphite layers has been identified as the key to ultra-low friction in dry friction. In our own previous work, the superlubricity of fluids (friction coefficients < 0.01) was successfully demonstrated using a mesogenic fluid. These results have generated a strong interest in translating these findings into practical applications. The main challenge is to maintain superlubricity under application-specific conditions to ensure long-term lubrication.

To address this challenge, tribological studies were conducted on various lubricants, materials (such as ceramics) and coatings (including a-C:H and ta-C) using a model friction test. After an initial run-in period, velocity ramps (Stribeck curves, 0-1.4 m/s) were performed to evaluate friction under different lubrication conditions. Subsequently, the most promising candidates were application tested on a plain bearing tribometer.

Our results show that superlubricity can be achieved by selecting the right combination of friction partners and an intermediate medium, resulting in superior performance compared to a reference oil. Superlubricity can be achieved in both boundary and mixed friction ranges and in the hydrodynamic range, although not over the entire speed spectrum. By selecting the most suitable materials and model lubricants, we were able to conduct targeted, application-oriented plain bearing experiments that demonstrated superlubricity over a wide speed range.

The experiments identified promising tribosystems capable of achieving superlubricity, particularly with steel balls against ceramics or DLC coatings lubricated with glycerin. However, it is important to note that the model lubricants and coating systems used need to be further optimized to match the specific application parameters and lubrication conditions.

This research work is a crucial step towards the realization of sustainable and energy-efficient tribosystems.