Surface graphitized modification is an effective method to improve the friction performance of amorphous carbon (a-C) films. However, traditional modified methods, such as metal catalysis, extra addition of graphite or graphene, and annealing, often come with drawbacks of complex operation, structural damage of graphitized layer and intrinsic a-C films and so on. In this study, a novel approach is explored to achieve in-situ surface graphitization of a-C films by short-term laser irradiation. Especially, as a key parameter, the influence of laser irradiation power on surface graphitization structure, and mechanical and tribological properties of a-C films was emphasized. Results indicate that surface in-situ graphitization is obtained successfully on the surface of a-C films by laser irradiation, and the surface graphitization degree is positively correlated with the laser irradiation power. Importantly, the obvious curled graphene structure is formed on the a-C films after laser irradiation. Compared with the intrinsic a-C film, the hardness and elastic modulus of graphitized film surface show an obvious reduction after laser irradiation but without significantly deteriorating the internal mechanical properties of a-C film, and also decrease gradually with the increase of laser power, which is related to the enhancement of sp²-C structure. Notably, in-situ surface graphitized modification induced by laser irradiation exhibits an obvious effect in friction reduction, 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.