Molecular Dynamics Simulations On Micro-Structure And Tribological Properties Between Silicon Incorporated Diamond-Like Carbon Films

Diamond like carbon (DLC) films have been extensively studied over the past decades due to their unique combination of properties, such as low friction coefficient, high hardness, high wear resistance and chemical inertness. DLC films have become technologically important materials, used in mechanical applications. But DLC films have some defects and can not be sufficient for special needs in industries. Recently years, the tribological properties of DLC films can be improved by adding other metal or non-metal elements. At present it has been found that, in particular, silicon-incorporated DLC (Si-DLC) films are of significant interest for tribological effects, they possess the potential to improve wear performance in humid atmospheres and at higher temperature by adding silicon. However, the result showed that the micro-structure and tribological properties of Si-DLC films were significant affected by adding silicon, and the mechanism of action in the slide by adding silicon is not clear. Therefore, molecular dynamics (MD) simulations were used to study micro-structure and tribological behavior of Si-DLC films at different silicon contents from 0 to 50% in this paper.Firstly, three-dimensional structures of Si-DLC films at the density 2.6 g/cm3 by melting and annealing of MD simulations were built, and then the parameters of the micro-structure of the Si-DLC films were analyzed. The results showed that the silicon atoms were almost surrounded by the carbon atoms in all Si-DLC films. Moreover, the sp3/sp2 ratio in the Si-DLC films increased with the increasing silicon content. But the Csp3/Csp2 ratio of only carbon atoms reached the minimum at the silicon content of 0.2, and then increased with the further addition of silicon. Bulk modulus and its variance both decreased with the increasing silicon content in the Si-DLC films.Secondly, the slide counter-face was produced by using a mirror image. The sliding results showed the silicon contents had greatly influenced the friction forces at stable stage. Variance of the friction forces decreased with the increasing silicon content in the Si-DLC films. The friction force increased with the increasing silicon content till the silicon content at 20%; then the friction force would slight decrease till the silicon content at 50%. The results of bond numbers of interfilms and intrafilms have showed that the silicon addition promoted the bonding of interfilms and intrafilms forming, which results in the friction force increased. Surprisingly, there were no C-C bond numbers between the Si-DLC films.The conclusions in the paper have a good agreement with the experiments, so they can provide a theory instruction for experimental study of the Si-DLC films, and will promote the application of the Si-DLC films into various industry areas.