Tailoring microstructure, mechanical and tribological properties of amorphous CNx films by incorporating Fe

Amorphous carbon nitride (α-CNx) films are perfect protective materials for advanced tribological application due to low coefficients of friction and chemical stability. However, their lower nano-hardness and poor degree of graphitization during sliding, result in the limited lubrication effect and inevitable wear, which greatly limits its wider potential for protective films. Herein, α-CNx/Fe films were constructed at different deposition temperatures by magnetron sputtering. The results indicated that the α-CNx/Fe film deposited at 600 °C has the highest hardness of ~27.3 GPa (2.13 times that of the pure α-CNx film), which is mainly attributed to the high sp3/sp2 carbon ratio. Besides, the FeN bond of the film can induce the formation of self-lubricating tribofilm on the worn surface, which leads to low friction coefficient (μ = 0.18) of the α-CNx/Fe film during sliding, only 46 % of pure α-CNx films. High-resolution transmission electron microscopy, Raman spectra, and Electron energy loss spectra further confirmed that most of the tribofilm on the worn surface is composed of graphitized onion-like carbon structure scrolls, which is the critical factor for the decrease of friction coefficient. These results demonstrated that the obtained CNx/Fe films have excellent lubrication characteristics, providing guidance for CNx-based films in advanced precision machining and tribological applications. •High hardness, self-lubrication α-CNx/Fe films have been prepared by sputtering.•The sp3/sp2 ratio plays a key role in the hardness enhancement.•α-CNx/Fe (600 °C) self-assembles to form an OLC tribofilm during the friction.•Fe-N bonds induce the formation of onion-like carbon tribofilm.