[SY-O4] A Molecular Dynamics Study on the Wear Mechanisms of Hydrogenated Diamond-like Carbon
Diamond-like carbon (DLC) is a promising solid lubricant and widely used as a lubricant coating in various industrial applications such as engine, hard-disk, and space instruments. Hydrogenated DLC coatings show the much better low-friction properties and lubricity than the non-hydrogenated DLC coatings. However, wear of the hydrogenated DLC coatings causes the reduction of the durability of DLC coatings and limits their utilization. For the further improvement of the hydrogenated DLC coatings, the deep and comprehensive understandings of the wear mechanisms of the hydrogenated DLC are very essential; nevertheless, these understandings are still lacking because the experiments are difficult to observe the complicated atomic-scale friction processes and tribochemical reactions at the interface. To handle these difficulties, we employ a molecular dynamics method to investigate the wear mechanisms of the hydrogenated DLC. We perform friction simulations in the vacuum by using the DLC models with a hydrogen concentration of 0%, 20%, 30%, 40%, and 50%. From the simulation results, we observe two wear mechanisms of DLC: 1) chemical wear as the generation of hydrocarbons desorbing from DLC surface and 2) mechanical wear as the transfer of carbon atoms to the counter substrates. The chemical and mechanical wear co-decide the wear behaviors of DLC. Furthermore, with increasing the hydrogen concentration in DLC, chemical wear increases and mechanical wear decreases, causing a parabolic-like hydrogen dependence of the total wear with a minimum value at the hydrogen concentration of 30%. Our simulations successfully give fundamental understandings about the wear mechanisms of the hydrogenated DLC and provide the theoretical instructions to improve the anti-wear properties of DLC coatings.