Vacuum are deposition of TiN, NbN and TiN/NbN multi-layer coatings

Single-layer coatings of TiN and NbN, and multi-layer coatings of TiN/NbN, were deposited onto WC-Co substrates using a triple-cathode vacuum are plas ma gun connected to a cylindrical plasma duct onto which an axial magnetic field was imposed. Additional magnetic fields were applied by two beam stee ring coils orientated normal to the duct axis. The magnetic field produced by the steering coils directed the plasma beam onto a substrate placed on t he system axis, increasing the plasma flux to the sample. The single-layer coatings were produced by generating Ti or Nb plasmas in a nitrogen backgro und at a pressure P in the range of 0.67 to 2.67 Pa. Multi-layer coatings w ith 20, 50 and 100 layers were deposited by alternately switching the arcs on Ti and Nb cathodes. Coating structure and composition were studied by me ans of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Micr ohardness and adhesion to the substrate were studied by Vickers' micro-inde ntation and scratch tests, respectively. It was shown that the phase composition of the NbN coatings depended on the deposition rate and P. The coatings deposited at low deposition rate (i.e. without the beam steering field) exhibited a single-phase cubic delta-NbN structure at P greater than or equal to 0.67 Pa, whereas the coatings depos ited with application of the beam steering field, at P=0.67 and 1.33 Pa, we re composed of a mixture of cubic delta-NbN and hexagonal NbN0.95, while at P=2 and 2.67 Pa, the hexagonal phase was not found. The phase composition of the TiN coatings was independent of the deposition rate and P in the ran ge 0.67-2.67 Pa. The highest microhardness (up to 38 GPa) and scratch criti cal load (80-95 N) were obtained for single-phase delta-NbN coatings deposi ted at P=0.67-1.33 Pa and at low deposition rate. The microhardness of mult i-layer TiN/NbN coatings of 3.2-3.6 mu m total thickness increased with inc reasing number of alternating layers, but did not exceed that of the pure d elta-NbN observed in this study. (C) 1999 Elsevier Science S.A. All rights reserved.