Surface in-situ graphitization and properties of amorphous carbon film induced by laser irradiation

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.