Using direct current plasma-enhanced chemical vapor deposition (PECVD) techniques, the nanocomposite coatings of nc-TiN/a-Si3N4 11 were deposited on stainless steel substrates. The coatings were characterized by nano-indentation, elastic recoil detection spectroscopy 12 (ERD), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The effects of 13 oxygen and chlorine were investigated in this paper. A certain content of oxygen and chlorine can strongly decrease the hardness of superhard 14 of nc-TiN/a-Si3N4. It is shown that 1-1.5 at.% of oxygen causes a decrease in hardness decrease to a value of about 30 GPa as compared to 15 45-55 GPa for a the that of below 0.2 at.% oxygen.