Effects of sp bond ratio and modulation ratios on nanotribology behaviors of diamond-like carbon coatings investigated using atomistic nanoscratching simulations.

Context: Diamond-like carbon (DLC) films are amorphous solids in which carbon atoms are linked by hybridized sp, sp, and sp bonds. The mechanical and tribological properties of DLC films can be adjusted by tuning the sp/sp bond ratio. These films are typically used as protective coatings for components such as dies, automotive engines, mechanical seals, hard disk drives, biological engineering devices, and micro/nano-electromechanical systems. Further exploration of the mechanical and tribological behavior of DLC films is important for enhancing functional design for the above applications. The simulation results show that single-layer DLC with a higher sp ratio has better resistance to indentation. Single-layer DLC with a lower initial sp ratio has lower friction and a shorter repeated cycle in the friction force curve due to an increase in the graphitization of the friction interface. Single-layer DLC with a higher sp ratio has a higher coefficient of friction because compared with the normal force, the friction force is much more sensitive to an increase in the sp ratio.

Methods: Molecular dynamics simulations based on the Tersoff potential were performed using the open-source code LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator).