Surface <i>in-situ</i> graphitization and properties of amorphous carbon film induced by laser irradiation

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.