The emergence of nanotechnology and surface engineering techniques provides new opportunities for designing self-lubricant coatings with enhanced properties. In recent years, green coating technologies have played a vital role in environmental preservation. This article mainly reviews five typical types of self-lubricant coatings including MoN coatings, VN coatings, WN coatings and TMN (Transition Metal Nitride) soft-metal coatings, and DLC (Diamond-like Carbon) with lubricant agents deposited by PVD (Physical Vapor Deposition) for the demanding tribological applications, which is the latest research into the green lubricant coatings. Furthermore, it is of great significance for designing the green self-lubricant coatings to adapt the demanding tribological applications to meet the industrial requirements.

The multilayered Mo₂N/Ag-SiN_x self-lubricant films were designed and deposited using a DC (Direct Current) magnetron sputtering system under mixed gas atmosphere of N₂ and Ar. The modulation ratio (thickness ratio of Mo₂N to Ag-SiN_x) was fixed at 2:1, while the modulation periods (thickness of Mo₂N and its adjacent Ag-SiN_x layer) were set at 20, 40, and 60 nm. The results indicated that all multilayer films, regardless of modulation period, exhibited a combination of face-centered cubic (fcc) and amorphous phases. Specifically, fcc-Mo₂N was detected in the Mo₂N layers, while fcc-Ag and amorphous SiN_x co-existed in the Ag-SiN_x layers. The multilayered architecture induced residual stress and interface strengthening, resulting in hardness values exceeding 21 GPa for all films. Compared to Mo₂N and Ag-SiN_x monolayer films, the multilayer structure significantly enhanced tribological properties at room temperature, particularly in terms of wear resistance. The Mo₂N/Ag-SiN_x multilayer films exhibit ~25% lower friction than Ag-SiN_x, ~3% lower than Mo₂N, and achieve remarkable wear rate reductions of ~71% and ~85% compared to Ag-SiN_x and Mo₂N, respectively, demonstrating superior tribological performance. The synergistic effects of both modulation layers and relative high hardness were key factors contributing to the enhanced tribological behavior.