Vacuum Thermal Treatment for Achieving Macroscale Superlubricity by Nanodiamond and Hexagonal Boron Nitride on H‐DLC Film Surfaces in Dry Nitrogen

Abstract Hydrogenated diamond‐like carbon (H‐DLC) films are limited by their poor thermal stability, which significantly affects the tribological applications and needs improvement. Accordingly, nanodiamond (ND) and hexagonal boron nitride (h‐BN) are used to address this issue. When the H‐DLC surface is deposited using ND+h‐BN mixture with mass ratio of 1:1 and a concentration of 0.1 mg mL⁻¹ and vacuum‐heated at 200 °C and 1 × 10⁻⁵ Pa, a superlow friction coefficient of 0.0015 can be obtained, with a reduction of 98.33% as compared to pure H‐DLC. Correspondingly, the wear rates of wear scar and wear track decreased by 81.95% and 24.83%, respectively. High vacuum thermal treatment can purify the adsorbed species on the surfaces of ND and h‐BN, and produce newly‐exposed dangling bonds. Simultaneously, new bonds of C‐N are formed between ND and h‐BN, and the nanoparticles adhere together to form a polymer‐like structure under friction. Furthermore, the ND can support h‐BN and reduce its agglomeration. Under the action of tribochemical reaction, the layer spacing of hexagonal boron nitride is increased to obtain a better shear slip. The combination of these factors resulted in ultra‐low friction. This study paved the way for developing functional anti‐friction additives for durable and high‐performance lubrication.