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.