Duplex doped nanocomposite carbon-based coating with self-lubricating performance

Nanocomposite TiC/a-C and TiC/a-C:Al carbon-based coatings were fabricated on stainless steel and silicon wafer substrates. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to investigate the composition and structure of as-fabricated coatings. Nanoindenter, interferometer, scratch tester and ball-on-disc tribometer were used to evaluate the mechanical and tribological properties. Results showed that the TiC nanocrystallites were formed and uniformly dispersed in the amorphous carbon matrix by incorporating strong-carbide-forming Ti metal while the size of TiC grain and surface roughness were decreased by co-incorporating weak-carbide-forming Al metal. Particularly, the co-incorporation of Al could drastically diminish the magnitude of internal stress, improve adhesion strength and maintain relatively high hardness for as-fabricated coating. As a result, the duplex doped nc-TiC/a-C:Al coating achieved lower friction coefficient and specific wear rate compared to simplex Ti-doped nc-TiC/a-C coating. Mechanism analysis revealed that the improved self-lubricating and anti-wear performances of this nc-TiC/a-C:Al coating were mainly attributed to the good combining mechanical properties and easily formed continuous and compacted graphitized interlayer on the contact area.

► nc-TiC/a-C:Al coating presents typical nanocrystallite/amorphous structure.
► nc-TiC/a-C:Al coating has superior combining mechanical properties.
► nc-TiC/a-C:Al coating easily forms continuous and compacted graphitized tribofilm.
► nc-TiC/a-C:Al coating exhibits improved self-lubricating and anti-wear behaviors.