Surface graphitization is an effective method for improving the friction performance of amorphous carbon (a-C) films. However, traditional modified methods, such as metal catalysis, addition of extra graphite or graphene, and annealing, often have drawbacks, such as complex operation, structural damage to the graphitized layer and intrinsic a-C films. In this study, a novel approach is explored to achieve in-situ surface graphitization of a-C films by short-term laser irradiation. In particular, as a key parameter, the influence of laser irradiation power on the surface graphitization structure and the mechanical and tribological properties of a-C films was emphasized. The results indicate that surface in-situ graphitization is successfully obtained on the surface of a-C films by laser irradiation and the surface graphitization degree is positively correlated with the laser irradiation power. Importantly, an obviously curled graphene structure is formed on the a-C films after laser irradiation. Compared with those of the intrinsic a-C film, the hardness and elastic modulus of the graphitized film surface obviously decrease after laser irradiation but without significantly deteriorated internal mechanical properties of the a-C film and also decrease gradually with increasing laser power, which is related to the increase in the sp²-C structure. Notably, in-situ surface graphitization induced by laser irradiation obviously reduces friction, which can be reduced by 25.41% compared with the intrinsic a-C film. This is attributed to the fast formation of the graphitized transfer film, which facilitates the transition of the friction interface from graphitized a-C surface/Al₂O₃ to graphitized a-C surface/graphitized transfer film.

The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon (a-C) films with extremely low friction. It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions. In particular, the interactions of hydrogen atoms and lubricants are confusing, which is enslaved to the in situ characterization technique. The reactive molecular dynamics (RMD) simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions. The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient (μ) of textured a-C film, which is highly dependent on the surface hydrogen content. The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material. Interestingly, with the enhancement of the surface hydrogen content, the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.