TiN, NbN, and TiN/NbN polycrystalline nanostructured multilayer films were deposited on high speed steel substrates by unbalanced reactive magnetron sputtering of Ti and Nb targets in Ar-N-2 discharges. Two techniques were used for obtaining a series of multilayers with compositional modulation period, Lambda, in the range 3.8-100 nm; rotation of a cylindrical substrate holder between two opposing cathodes or by positioning inclined cathodes above the substrate and using shutters. For the two setups, ions were accelerated from the discharge by a negative substrate bias V-s = 120-150 V and V-s= 100 V, respectively, with an ion-to-metal arrival rate ratio of similar to 1. The nanoindentation hardness and abrasive wear resistance by dimple grinding test of the coatings were compared between the sample series and related to the microstructure, phase composition, and residual stress sigma(res) obtained by transmission electron microscopy, x-ray diffraction, and substrate curvature technique, respectively. All films exhibited a dense and columnar microstructure with 20-90 nm grain sizes. Nanoindentation test of the high-V-s series showed similar hardness for TiN/NbN nanostructured multilayers and homogeneous films in the range of 32-34 GPa. For the low-V-s series, mixed-phase hexagonal beta-Nb2N/cubic delta-NbN films exhibited the highest hardness of 39 GPa, TiN had the lowest hardness with 26 GPa, and TiN/NbN multilayers had values in between. The absence of superlattice hardening in the polycrystalline TiN/NbN nanostructured multilayer is suggested to be due to microcracking at grain boundaries under the indentor tip. For both series, sigma(res) was lower for the multilayers than the corresponding homogeneous films. The low-V-s multilayers exhibited sigma(res) less than or equal to 1.6 GPa for Lambda less than or equal to 16.6 nm, more than a factor of 2 smaller than for homogeneous TiN, NbN, and TiNbN-alloy films. High-V-s multilayers had sigma(res) similar to 4 GPa. The abrasive wear resistance of films between sample series showed a negative correlation with grain size. Films of the high-V-s series exhibited higher wear resistance compared to the corresponding films of the low-V-s series. Wear constants of high-V-s beta-Nb2N films and TiN/NbN multilayers were as low as 28 and 40 mu m(3) mm(-1) N-1, respectively. (C) 1998 American Vacuum Society. [S0734-2101 (98)03605-7].
