A facile strategy to synthesis nanocrystalline H-Diamond (H-D) phase in MoCx (H-D/a-C) composite coatings using a reactive sputtering system: The role of Mo content

In the magnetron sputtering system, using an unbalanced magnetic field configuration in the cathode is a privileged strategy for designing protective coatings on metal substrates for the specific application. In the present study, A105 carbon steel substrates coated with MoCx (H-D/a-C) composite films (H-D: hexagonal dia-mond, a-C: amorphous carbon) utilizing an unbalanced magnetron (UBM) sputtering technique. The effects of (Mo/C+H) ratio on microstructure, mechanical and tribological characteristics of MoCx (H-D/a-C) composite coatings were investigated. MoCx (H-D/a-C) coated A105 carbon steel substrates showed enhanced mechanical and tribological performance. The Mo content strongly affected the bonding structure of MoCx (H-D/a-C) composite coatings. The results from Raman spectroscopy showed that the coatings contain a high value of sp2 carbon bonding, and its affluence increases with increasing (Mo/C+H) ratio. For the first time, the H-Diamond phase was successfully formed in all the UBM sputtered MoCx (H-D/a-C) composite coatings, while Mo acted as a catalyst for the nucleation and growth of H-Diamond phase. The MoCx (H-D/a-C) composite coatings with more H-Diamond phase and higher Mo content showed higher hardness and plasticity index, lower coefficient of friction (COF) and wear rate. The results confirmed that MoCx (H-D/a-C) coated A105 carbon steel substrates can be potentially applied to protect the surface of the perforated spherical ball of ball valves.