Synergy between h-BN tribo-catalytic graphitization and CH4 gas passivation: Achieving ultralow friction in diamond-like carbon film

Optimizing the tribological performance of moving components with lubricating materials is crucial for reducing energy consumption and carbon footprint. Spin-coating two-dimensional materials represents an effective approach to lowering the friction coefficient of typical lubricating materials such as diamond-like carbon (DLC). However, the influence of third-body introduction on lubricant–environment interfacial interactions remains unclear. Herein, h-BN, which catalyzes carbon graphitization, was selected to systematically investigate its regulatory effect on the tribological behavior of DLC under an energy-gas CH 4 atmosphere. The synergistic effect between the tribo-catalytic action of h-BN and the intrinsic structure of the films leads to significant differences in the degree of friction coefficient improvement for DLC with distinct bonding structures: the friction coefficient of low-sp 3 -content DLC is reduced by 45%, while that of high-sp 3 -content and high-sp 2 -content DLC is significantly enhanced with a reduction of no less than 20%. Structural characterization of the tribological interface reveals that h-BN catalyzes graphitization at the sliding interface, transforming the transfer film on the wear scar from a Gr/amorphous carbon superlattice structure into a coexisting structure of continuous graphene and amorphous carbon. The formation of continuous graphene suppresses interfacial dehydrogenation and strengthens surface passivation. This study reveals the competitive mechanism between third-body tribo-catalytic graphitization and shear-induced gas adsorption at the DLC sliding interface, providing a new strategy for the design of ultra-low-friction DLC films.