Optimization of chromium nitride (CrNx) interlayers for hydrogenated amorphous carbon (a-C:H) film systems with respect to the corrosion protection properties by high power impulse magnetron sputtering (HiPIMS)

Chromium nitride (CrNx) films are frequently used as interlayers to enhance the adhesion of hydrogenated amorphous carbon (a-C:H) films on steel substrates. The microstructure of these CrNx interlayers has a direct influence on the corrosion protection properties of the a-C:H films. A dense and defect-free microstructure can improve the corrosion resistance. In this study, chromium nitride (CrNx) films were optimized by high power impulse magnetron sputtering (HiPIMS) in order to reduce the film defect density. The HiPIMS-CrNx films were deposited on polished AISI 52100 (100Cr6) steel shims with a hardness of 60 ± 2 HRC using a Cemecon CC800®/9 HiPIMS device. The influence of the cathode pulse duration, cathode frequency and bias pulse duration on the deposition rate, nitrogen content, phase composition, microstructure and mechanical properties of CrNx films were investigated by glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD), electron microscopy and microhardness measurements. Additionally, the corrosion resistance of HiPIMS-CrNx/a-C:H-coated 100Cr6 steel shims was tested by neutral salt spray test. For lower duty cycles an enhanced corrosion protection was observed due to a densification of the CrNx film microstructure and a decrease of the film defect density.