Tribosimulation of ta-C nanocoatings

Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed automotive engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency.
The present study employs atomic-scale simulations to investigate the basic principles of wear and friction between hydrogen-free tetrahedral-amorphous carbon (ta-C) films. The ta-C films are modeled state-of-the-art by an improved version of the well-known Brenner bond-order potential [1,2], which had been successfully applied to elucidate the wear processes during diamond polishing[3].

Our work starts with the preparation of ta-C film structures with different atomic densities, which are then characterized with respect to local and global film properties in comparison to experimental data. With these prepared nanocoatings, we perform computational sliding experiments to investigate mechanisms of friction and wear between interacting ta-C surfaces. Dry and lubricated sliding is considered. Especially for dry sliding and during tribological contact, these diamond-like films (mainly sp3 hybridized) tend to form a soft-amorphous or graphite-like tribomaterial mainly consisting of carbon atoms in sp2 configuration. We discuss underlying mechanisms of the dynamic triboreactions and investigate tribological properties such as shear forces at the sliding interface.