Hydrogenated amorphous carbon (a-C:H) films are capable of offering superior friction reduction and wear resistance when rubbed in both dry and lubricated interfaces. However, the inherent mechanisms governing fretting wear in a-C:H films are still not well comprehended. Herein, atomic-scale analysis is conducted to unveil the relationship between interfacial tribofilms and the fretting wear behaviors. The results emphasize the determining role of the structural evolution in tribofilms with experimental temperature. The room temperature (RT) fretting experiment establishes a bilayer nanostructured tribofilm, with a C-rich transfer layer established on a Fe-rich tribo-sintered layer. As the fretting temperature elevates the graphitization degree of the tribofilms exacerbates, and surface oxidation and hydrogen effusion arise in the a-C:H film, which induce higher friction coefficient and wear rate. Chromium outward diffusion at 500 ℃ establishes a Cr-rich interlayer in the tribofilm, which forms interfacial chromium-carbon bonds, promotes adhesive carbon transfer, and brings about the sharp increase of the friction force and wear rate. These findings provide new insights into the fretting wear mechanisms, and provide guidance for the application of a-C:H films in elevated-temperature fretting scenarios such as aero-engines tenon and spline connections.

hydrogenated amorphous carbon films; tribofilm; nanostructure; fretting wear; temperature