Two-dimensional (2D) materials with a layered structure are excellent candidates in the field of lubrication due to their unique physical and chemical properties, including weak interlayer interaction and large specific surface area. For the last few decades, graphene has received lots of attention due to its excellent properties. Besides graphene, various new 2D materials (including MoS ₂ , WS ₂ , WSe ₂ , NbSe ₂ , NbTe ₂ , ReS ₂ , TaS ₂ and h-BN etc.) are found to exhibit a low coefficient of friction at the macro- and even micro-scales, which may lead to widespread application in the field of lubrication and anti-wear. This article focuses on the latest development trend in 2D materials in the field of tribology. The review begins with a summary of widely accepted nano-scale friction mechanisms contain surface friction mechanism and interlayer friction mechanism. The following sections report the applications of 2D materials in lubrication and anti-wear as lubricant additives, solid lubricants, and composite lubricating materials. Finally, the research prospects of 2D materials in tribology are presented.

A common belief proposed by Peierls and Landau that two-dimensional material cannot exist freely in a three-dimensional world has been proved false when graphene was first synthesized in 2004. Graphene, which is the base structure of other carbon materials, has drawn much attention of scholars and researchers due to its extraordinary electrical, mechanical and thermal properties. Moreover, methods for its synthesis have developed greatly in recent years. This review focuses on the mechanism of the thermal growth method and the different synthesis methods, where epitaxial growth, chemical vapor deposition, plasma-enhanced chemical vapor deposition and combustion are discussed in detail based on this mechanism. Meanwhile, to improve the quality and control the number of graphene layers, the latest research progress in optimizing growth parameters and developmental technologies has been summarized. The strategies for synthesizing high-quality and large-scale graphene are proposed and an outlook on the future synthesis direction is also provided.

Multi-layered graphene was prepared by supercritical CO₂ exfoliation of graphite. As the additives of polyalphaolefin-2 (PAO2) oil, its tribological properties were investigated using four-ball test method. The friction reduction and anti-wear ability of pure lubricant was improved by the addition of graphene. With a favorable concentration, the graphene was dispersive. The PAO2 oil with 0.05 wt % graphene showed better tribological properties than that for the other concentration of graphene additives. It could be used as a good lubricant additive for its excellent tribological characteristics, and the multi-layered graphene can bear the load of the steel ball and prevent direct contact of the mating metal surfaces. However, a higher concentration would cause the agglomeration of graphene and weaken the improvement of tribological properties.

With rapid economic development in China, demand for energy and transportation is growing. Due to the limitations of factors such as terrain and traffic, a large number of buried oil and gas pipelines are parallel to high-voltage transmission lines and electrified railways over long distances. Alternating current (AC) corrosion of pipelines is very serious in such cases. In this work, laboratory experiments were carried out with an electrochemical method in a simulated soil solution at various AC current densities from 0 to 200 A/m² and AC frequencies from 10 to 200 Hz. Experimental results indicated that with an increase in the AC current density, the corrosion potential of an X60 steel electrode shifted negatively, the anodic current density increased significantly, and the corrosion rate increased. Moreover, with an increase in the AC frequency, the corrosion potential of the X60 electrode shifted positively and the anodic current density decreased, which led to a decrease in the corrosion rate. Furthermore, the morphology of X60 electrodes indicated that uniform corrosion occurred at a low AC current density; while corrosion pits were found on the X60 electrode surface at a high AC current density, and deep corrosion pits seriously damaged the pipelines and might lead to leakage.