Cavitation erosion of CrN/CrCN multilayer coating

Results of investigations of multilayer CrN/CrCN coating - X6CrNiTi18-10 stainless steel substrate system exposed to cavitation degradation are presented. CrN/CrCN coating with six CrN + CrCN bilayers was deposited using cathodic arc evaporation PVD method. Cavitation erosion tests showed that deposition of CrN/CrCN coating increased incubation period, but cumulative mass loss of the CrN/CrCN - X6CrNiTi18-10 system was higher than that of the steel substrate one. Microscopic study revealed that the degradation process was dominated by fatigue. Austenitic steel fractured in a mixed mode with domination of a ductile mode, while the CrN/CrCN coating fractured mainly in a brittle mode. Degradation of the CrN/CrCN coating was accelerated by delamination that decreased coating toughness. A highly eroded zone of the coated specimen was of similar size to the steel specimen one, but the whole eroded area was much smaller. Performed investigation indicated that the CrN/CrCN coating is not resistant to high-velocity impacts of micro-jets. Other impacts caused coating undulation and removal of micro-droplets formed during coating deposition. The main reason of brittle fracture was high stiffness of the coating and high-velocity impacts of cavitation pulses.