In the past years many research works have been performed on the deposition of hard coatings (>40 GPa). Besides the mechanical properties, the thermal stability and the oxidation resistance at high temperatures have also been driving forces for the development studies. The addition of different elements, such as Al, Cr or Si, to transition metal nitrides has been one of the solutions to reach simultaneously very high hardness and excellent behavior at high temperatures. The aim of this research work was to deposit by sputtering amorphous W-Si-N coatings and to crystallize them by thermal annealing in Ar+H-2 atmospheres. The coatings were characterized before and after thermal annealing and the chemical composition and structure were co-related with the mechanical properties. All the coatings crystallized at temperatures lower than 1000degreesC, depending on their Si and N contents, with the formation of the bcc W-phase and/or silicide phases (W3Si, W5Si3 or WSi2). For the highest annealing temperatures, other phases containing elements from the substrate were also detected due to inter-diffusion between the films and the substrates. After thermal annealing a strong increase in the hardness of the films was registered in comparison to the as-deposited state. Values as high as 40 GPa were reached in some cases. However, a decrease in the hardness was observed after annealing at 1000degreesC due to the formation of phases with elements from the substrate and/or by the structural recovery of the films, including grain growth. Ratios H/E higher than 0.1 were reached envisaging a good tribological behavior for the W-Si-N films. (C) 2003 Elsevier B.V. All rights reserved.