Hardness versus structure in W-Si-N sputtered coatings

In this research work the influence of the addition of Si on the structure, morphology and hardness of W-(N) coatings was studied. The films were deposited by reactive sputtering from a W target superimposed with increasing number of Si small plates. The partial pressure ratio between nitrogen and argon was varied in the range 0-2. Thus, nitrogen content was in the range 0-60 at.%, and the silicon-to-tungsten contents ratio reached, for the greatest number of silicon plates, 0.5. Depending on the nitrogen content, the structure of the films varies from the single b.c.c. tungsten phase to the f.c.c. NaCl-type W2N. The synergistic action of both Si and N can originate the formation of amorphous structures. The hardness of the films was determined by ultramicroindentation technique by using either low loads (70 mN) and/or an empirical model which allows to eliminate the influence of the substrate on the measured values. Hardness values as high as 50 GPa was obtained. Generally, the films containing amorphous phases present lower hardness values than crystalline ones. (C) 1999 Elsevier Science S.A. All rights reserved.