Structural evolution and tribological behavior of nitrogen-doped DLC coatings deposited by pulsed DC PACVD method

In recent years, the stability of wear behavior for diamond-like carbon (DLC) coatings is very crucial and challenging. However, insufficient adhesion of the DLC coating to the substrate makes some problems for its wear application. Nitrogen doped in DLC coatings was prepared by D.C. Pulsed Plasma Assisted Chemical Vapour Deposition (PACVD) technique on the H13 Tool Steel under different conditions to improve the adhesion and finally tribological properties. The coating structure was assessed with Visible Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The mechanical and tribological properties of the coatings were evaluated by nanoindentation technique and rotational ball-on-disk tribometer. The results revealed that as the nitrogen content in the coatings rises, the friction coefficient of the coatings is more stable, however, it is higher than the other coatings at the beginning of the sliding distance. Therefore, the nitrogen-doped DLC coating deposited with the highest nitrogen gas flow rate (N2 = 10sccm) at 120 °C, demonstrated the best adhesion quality of the coating to the substrate (with a hardness of 15.39 GPa) and a stable friction coefficient of 0.24 at the end of the test and lowest wear rate of 1.15 × 10−6 mm3/Nm.