Synergistic effect of plasma nitriding and bias voltage on the adhesion of diamond-like carbon coatings on M2 steel by PECVD

Diamond-like carbon (DLC) coatings have excellent mechanical and tribological properties, as well as good wear and corrosion resistance. They are well established in medical, metalworking and automotive applications. However, further improvements are needed and substrate pre-treatment plays an important role in supporting and enforcing the adhesion and service performance of the DLC coatings. In this work, the synergetic effect of low-pressure arc plasma-assisted-nitriding (PAN) treatment of M2 steel and plasma-enhanced chemical vapor deposition (PECVD) on the DLC coatings adhesion was analyzed. Adhesion strength of a nitriding + DLC duplex coating system was compared to the performance of DLC-coatings applied on non-nitrided M2 steel substrates. The nitrided layer was analyzed by optical microscopy, electronic microscopy, X-ray microanalysis, X-ray diffraction, Vickers microhardness and atomic force microscopy. DLC coatings were analyzed using Raman spectroscopy revealing that DLC a-C:H type was obtained. The adhesion properties were analyzed by scratch testing supported by optical microscopy and scanning electron microscope, showing results with an improvement of the DLC's adhesion on the nitrided surfaces. •The combined process (PAN and PECVD) increased the DLC's coating adhesion to a M2 steel surface.•A DLC with 20 at.% hydrogen and 40–60% sp3 was obtained corresponding to type a-C:H.•Roughness from nitrided is an important factor in DLC's adhesion on M2 steel surface.