Friction behavior of diamond-like carbon coatings with different sp3 contents by atomistic-scale friction dynamics

The tribological performance of diamond-like carbon (DLC) coatings as a function of sp3 concentrations was investigated using molecular dynamics and experimental analysis. The results show that sp3 bonds proportion, hardness, and elastic modulus present an uptrend, whereas surface roughness displays a downtrend with the increase of SBV. Adhesive debris elements and no furrows features of the DLC coatings at low SBVs indicated the wear mechanism is dominated by adhesive wear. The DLC coatings at high SBVs were featured by obvious furrows and stacked abrasives, suggesting abrasive-wear-dominated. Atomistic-scale friction dynamics were used to reveal the friction mechanism. Interactions with the Si3N4 friction pair changed from carbon atoms chains or single atoms to atom groups with the increase of biases. The formation of the interfacial bonds changed from CN covalent bonds to CC covalent bonds. At high biases, there was a dissociation of many internal CC bonds that occurred in the DLC coatings. The bond evolution in friction simulation indicated the tribological mechanism transformed from adhesive wear to abrasive wear with an increase of the SBV. The DLC coating at the SBV of −30 V was located at the transformation point of two wear mechanisms, showing a well-established wear resistance.