Abstract
The tribological properties, under water-lubricated conditions, of three major nano-composite coatings, i.e., diamond-like carbon (DLC or a-C), amorphous carbon nitride (a-CNx) and transition metallic nitride-based (TiN-based, CrN-based), coatings are reviewed. The influences of microstructure (composition and architecture) and test conditions (counterparts and friction parameters) on their friction and wear behavior under water lubrication are systematically elucidated. In general, DLC and a-CNx coatings exhibit superior tribological performance under water lubrication due to the formation of the hydrophilic group and the lubricating layer with low shear strength, respectively. In contrast, TiN-based and CrN-based coatings present relatively poor tribological performance in pure water, but are expected to present promising applications in sea water because of their good corrosion resistance. No matter what kind of coatings, an appropriate selection of counterpart materials would make their water-lubricated tribological properties more prominent. Currently, Si-based materials are deemed as beneficial counterparts under water lubrication due to the formation of silica gel originating from the hydration of Si. In the meantime, the tribological properties of nano-composite coatings in water could be enhanced at appropriate normal load and sliding velocity due to mixed or hydrodynamic lubrication. At the end of this article, the main research that is now being developed concerning the development of nano-composite coatings under water lubrication is described synthetically.
Highlights
Lubricant oil has been widely used in various driving systems in the machinery industry [1].the source of lubricating oil, i.e., petroleum, is non-renewable
It has been reported that the tribological properties of diamond-like carbon carbon (DLC) coatings under water lubrication lubrication were strongly dependent on their microstructure and test were strongly dependent on their microstructure and test conditions conditions, which will be stated in detail as follows
Hydrogen-free DLC (a-C) coatings are superior to hydrogenated DLC:H (a-C:H) coatings under water hydrogen-free DLC (a-C) coatings are superior to hydrogenated DLC:H (a-C:H) coatings under lubrication
Summary
Lubricant oil has been widely used in various driving systems in the machinery industry [1]. The proposal and development of green tribology, i.e., environmentally-friendly tribology, have become a priority to minimize pollution and conserve petroleum resources [2,3] Under such a background, water lubrication as a favorable alternative has intensively attracted academics concerns. The deposition of nano-composite coatings a relatively easy protect tribopairs water lubrication It takes the advantage the ductility of the metal inexpensive way under to protect tribopairs under water lubrication. As well as an increasing citation number per year (Figure 1) It is obviously obviously indicated more and and more moreacademics academicsaround aroundthe theworld world have started engage themselves in indicated that that more have started to to engage themselves in the the study ofthe friction and wear behaviors of nano-composite coatings under water lubrication [13].
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