Effect of substrate bias voltage on the properties of CrCN and CrN coatings deposited by cathodic arc evaporation

The substrate bias voltage is one of the significant parameters of technology controlling the mechanical properties of PVD coatings. Chromium nitride and chromium carbonitride coatings were deposited on HS6-5-2 steel substrates by cathodic arc evaporation technique. The relationships between one of deposition parameter, negative substrate bias voltages Vs (10 V–300 V), and the coatings characterization such as microhardness, stress, adhesion of the coatings, elastic strain to failure related to H/E ratio were investigated. On SEM photos one can observe a dense polycrystalline structure with columnar grains for the coatings deposited at low bias voltage and homogenous, fine-grained morphology obtained at higher bias voltage. Residual stresses were measured by substrate curvature technique. The CrN coatings show a compressive residual stress that increases from 1.0 (Vs = −10 V) to 2.1 GPa (Vs = −70 V). At higher bias voltages a decrease of the compressive residual stresses is apparent. Similar relation but for higher stress values is observed for CrCN coatings. Nanoindentation showed a maximum hardness of 25 GPa for CrN and 26 GPa for CrCN coatings deposited at −150 V of bias voltage. The critical loads of CrN coatings in a scratch test decreased monotonically from 95 N to 78 N with increasing negative substrate bias voltage. The critical load of CrCN coatings was nearly constant, about 78 N.