Progress on Engineering Oriented Solid Superlubricity

According to statistical information, 30% of the world’s primary energy resources are exhausted by friction, and 80% of the mechanical component failures are led by wear. Eliminate friction and wear are everlasting goals for energy saving and service life prolonging with improved reliability of mechanical systems. Achieving "zero" friction and wear is the ultimate end of lubrication. It is one of the keys to ensure high precision, high reliability, long life and stable operation of mechanical system and promote energy saving and emission reduction. Superlubicity, also named “superlow friction, superlubricious friction, superlubritive friction, superlubric friction”, which is defined by Michio Hirano and Kazumasa Shinjo that two contact surfaces are in incommensurate contacting state, and deeply understood via theoretical simulation and nano- or micro- or macro- scale experiments in more than thirty years, but to realize engineering oriented superlubricity is still a challenging. Until now, both solid and liquid based lubricants are used for realizing superlubricity between surfaces of engineering components. In comparation, solid materials are better candidates for applications in harsh environments with lower pollution. At present, the main candidates for solid superlubricity at engineering scale are two-dimensional materials and amorphous carbon thin films. Very recently, 2D materials, like graphene, mxene, black phosphorus and hexagonal boron nitride, are always reported with superlubiricity under incommensurate contact, as well as their heterogenous junctions of which lattices are irrational to each other. However, the growth of perfect crystal 2D materials with macro-scale is still a change, and with the increase of dimension, two contact plane of 2D materials will be wrinkling or fluctuating, which will suppress superlubricity. Thus, to scale up the structure superlubricity is still a challenge. On the other hand, carbon based films, for example, highly hydrogenated carbon films, fullerene-like hydrogenated carbon films or silicon doped carbon films, show superlow friction under different environment. This paper summarize the state-of-the art and development of these solid supelubricious materials from principle, experiment and engineering application. Firstly, first principles computational simulation of superlubricity is summarized via theoretical approach to the study of friction by first principles, superlubricity enabled by pressure-induced friction collapse and the difference between pressure induced superlubricity, structure superlubricity and continuous superlubricity. Secondly, structure superlubricity including nano and micro-scale superlubricity, particularity of macroscopic contact superlubricity and the design macro-scale superlubricity are discussed. At last, superlubricity of carbon based films, about superlubricity of highly hydrogenated carbon films, fullerene-like hydrogenated carbon films and superlubritive properties of carbon films hybride with oils, are stated. At the end of the summary section, the existing problems of engineering-oriented superlubricity as well as prospects for future development are summarized. © 2023 Science Press. All rights reserved.