Single-layer MoN coatings deposited by vacuum-arc method in the mode of plasma assistance

Abstract

A possibility is shown for changing the elemental and phase compositions of coatings based on molybdenum nitrides, synthesized by vacuum-arc method with plasma assistance, by varying the discharge parameters of the gas plasma source at the constant pressure and composition of gas mixture. It is shown that the coatings formed in the plasma-assisted modes do not practically contain any metallic phase. All coatings of the Mo–N system, deposited in the plasma-assisted modes, have multiphase compositions: β-Mo2N, γ-Мо2N, δ-MoN. As the nitrogen concentration is increased, the volume fraction of δ-MoN phase increases to 67%. The coatings have columnar structure, where the transverse size of the columns is within 2−113 nm. They possess a substructure: the columns consist of nanosized crystallites. The dimensions of Mo2N crystallites lie within the range of 2.1−7.0 nm, and those of MoN-crystallites – 1.7−7.4 nm. It is revealed that the formating δ-MoN phase is accompanied by an alternating plate-like structure of the MoN/Mo2N/…/MoN/Mo2N type. This structure, as the concentration of nitrogen in MoN coatings increases, prevails, and the alternating plates form packs with a transverse size of up to 200 nm. It is shown that the increase in the concentration of nitrogen and volume fraction of δ-MoN phase results in a decrease of the average transverse size of Mo2N columns from 37 to 12 nm. It is determined that formed MoN coatings possess high hardness (up to 36 GPa) and wear-resistance (wear rate ~10−7 mm3N−1m−1).