Effect of nitrogen pressure, bias voltage and substrate temperature on the phase structure of Mo-N coatings produced by cathodic arc PVD

In this study, the effect of nitrogen pressure, bias voltage and the substrate temperature on the structure of Mo-N coatings produced by arc PVD was investigated. High speed steel substrates were coated at 1.9, 1.5, 1.2, 0.8 and 0.4 Pa nitrogen pressures by using -150, -250 and -350 V bias voltages. The coating procedures were performed at two temperature ranges: at 410-510 °C and at 300-380 °C. At the nitrogen pressure of 1.9 Pa and bias voltage of -150 V, δ-MoN (hexagonal) phase was obtained. When the pressure decreased to 1.5 and 1.2 Pa, mixed phases of δ-MoN and γ-Mo₂N were produced. At lower nitrogen pressures of 0.4 and 0.8 Pa coatings consisted mainly of γ-Mo₂N. At higher bias voltages it was impossible to produce single phase δ-MoN even at the highest nitrogen pressure (1.9 Pa). At lower nitrogen pressure and higher bias voltages cubic γ-Mo₂N was the predominant phase. Lower substrate temperatures promoted the formation of δ-MoN phase. The hardness of the coatings changed from 3372 to 5085 kg/mm² depending on the ratio of phase components in the coatings.