Investigation of the structural and tribological effects of silicon and nitrogen doping in hydrogenated amorphous carbon coatings applied to AISI M35 high-speed steel substrates

Hydrogenated Amorphous Carbon Coatings have been used in forming and machining tools, demonstrating solid lubrication capabilities, chemical inertness, wear resistance, and a reduction in the coefficient of friction. However, studies still report adhesion issues, which are often correlated with the residual stress state. Doping techniques have been used to mitigate this problem and, additionally, to improve the tribological performance of the coatings. In this study, nitrogen and silicon doping techniques were applied to hydrogenated amorphous carbon coatings deposited on AISI M35 high-speed steel. In the methodology, three types of coatings were deposited onto substrate samples and subsequently analyzed using structural, chemical, physical, and tribological characterization techniques. The results showed that nitrogen doping can increase sp³ hybridizations more than silicon doping. The sp³/sp² ratio appeared to be higher (0.56) with nitrogen doping compared to silicon (0.31). Nitrogen addition resulted in the hardest (≈ 14 GPa) and stiffest (≈ 130 GPa) coating, as well as the best adhesion to the substrate. Regarding silicon, the coating exhibited the greatest thickness (≈ 5 μm), the lowest hardness (≈ 6 GPa) and stiffness (≈ 46 GPa). Nevertheless, it showed the best performance in the micro-abrasive wear test: the worn volume represented only 4 % of the volume measured on the uncoated sample and also presented the lowest coefficient of friction (≈ 0.1).