Synthesis and characterisation of sputtered hard coatings within the system Cr-N/WSX

CrNx-WSx films were deposited by unbalanced magnetron cosputtering and their structure was investigated as well as their mechanical and tribological properties. A Cr target with WS2 inserts was used to adjust coverage fractions of the erosion track of 25 and 37.5 area%. Deposition was done in an Ar/N-2 atmosphere with different nitrogen fractions (p(N2) =0, 11 and 28%). Chemical analysis and crystalline structure were investigated by electron probe microanalysis and X-ray diffraction. Hardness and indentation modulus were determined by microindentation, stresses were measured by the substrate curvature method and the tribological behaviour of the coatings was evaluated by dry sliding ball on disc tests. With increasing p(N2), a transformation from a Cr solid solution to a Cr2N dominated structure was observed, which resulted in a moderate increase in hardness and elastic modulus. Owing to the observed substoichiometry of the formed WS2 phase, no friction reduction compared to single phase CrN coatings was obtained.