Modulation of bonding structure and mechanical properties of DLC coatings by binary doping: Molecular dynamics simulation

Diamond-like carbon (DLC) coatings are among the most promising wear-resistant materials for piston ring-cylinder liner (PRCL) systems. However, their widespread application is limited by poor adhesion to substrates and high internal stresses. In this study, we employed molecular dynamics (MD) simulations to investigate the properties of DLC coatings doped with binary carbophilic elements (Si/Cr) at varying atomic fractions. The bonding structure and mechanical properties were analyzed using radial distribution function (RDF), coordination number (CN), nanoindentation, shear strain, and von Mises stress distributions. The results show that the sp³ hybridization fraction decreased to 66.9 % in the S10 sample (Si 10 at.%). The S2 sample (Cr 10 at.%) exhibited the highest hardness and elastic modulus, reaching 110.03 GPa and 244.15 GPa, respectively—an improvement of 31.9 % and 18.4 % compared to the pure DLC (S1) sample. The S7 sample (Cr 4 at.%, Si 6 at.%) achieved the highest H/E_S ratio (0.441), which was 22.5 % higher than that of S1(pure DLC), indicating enhanced wear resistance and reduced susceptibility to plastic deformation. Shear strain and von Mises stress distributions after nanoindentation revealed isotropic material behavior and hemispherical shear strain diffusion in the doped samples. Notably, the S7 sample exhibited the lowest von Mises stress (134.5 GPa), 69 % reduction relative to pure DLC. In conclusion, binary doping (Si/Cr) significantly improved the mechanical properties, wear resistance, shear strain distribution, and von Mises stress response of DLC coatings compared to undoped DLC. Considering both wear resistance and plastic deformation resistance, the S6 coating demonstrated optimal performance. This study provides valuable insights for enhancing the performance and applicability of DLC coatings in industrial applications.