Evolution of tribo-induced interfacial nanostructures governing superlubricity in a-C:H and a-C:H:Si films

Abstract

Hydrogenated amorphous carbon (a-C:H) is capable of providing a near-frictionless lubrication state when rubbed in dry sliding contacts. Nevertheless, the mechanisms governing superlubricity in a-C:H are still not well comprehended, mainly due to the lack of spatially resolved structural information of the buried contact surface. Here, we present structural analysis of the carbonaceous sliding interfaces at the atomic scale in two superlubricious solid lubricants, a-C:H and Si-doped a-C:H (a-C:H:Si), by probing the contact area using state-of-the-art scanning electron transmission microscopy and electron energy-loss spectroscopy. The results emphasize the diversity of superlubricity mechanisms in a-C:Hs. They suggest that the occurrence of a superlubricious state is generally dependent on the formation of interfacial nanostructures, mainly a tribolayer, by different carbon rehybridization pathways. The evolution of such anti-friction nanostructures highly depends on the contact mechanics and the counterpart material. These findings enable a more effective manipulation of superlubricity and developments of new carbon lubricants with robust lubrication properties.

Unusual Competitive and Synergistic Effects of Graphite Nanoplates in Engine Oil on the Tribofilm Formation

“…The sp 2 ‐C bond fraction (%) was calculated according to the formula below where I s represents the integrated intensities from the tribofilm sample, the reference sample of highly oriented pyrolytic graphite (100% sp 2 ‐C bond) is denoted as I r . The EELS spectrum data (Figure S16, Supporting Information) was reproduced from Chen et al with permission from Nature Publishing Group. The referenced ratio I π* /( I π* + I σ* ) was calculated as around 0.28 by applying an energy window of 8 eV in the case of π* features and 15 eV for π* + σ* features.…”

Nanomaterials in Superlubricity

“…For the reported graphite and metal substrates, superlubricity can be obliterated by the increased loading condition which causes stress‐induced commensuration and elasticity‐induced local commensurability . Recently, ceramic substrates supporting graphene heterostructures were highlighted to provide the possibility of robust superlow friction, which can be realized from the mismatch of lattice constants and random orientations of constituent layers of the heterostructures.…”

“…The frictional performance of materials, particularly their superlubricity behavior in which friction completely or nearly vanishes, have received increasing interest . Superlubricity with a state of friction coefficient below 0.001, first proposed by Hirano and Shinjo, has been considered to be one of the most effective ways to alleviate the negative effects of friction and wear.…”

Enhancement in the tribological properties of Cr/DLC multilayers in methane: structural transformation induced by sliding

“…The prevailing views about repassivation mechanisms are chemical termination and rehybridization. Chemical termination has been proved by experiments and simulations [26][27][28]. For example, DLC film exhibited lower wear and friction under humid environments than under vacuum or dry gas [29].…”