New superhard Ti-Al-Si-N films, characterized by a nanocomposite comprising nano-sized (Ti,Al,Si)N crystallites embedded in amorphous Si3N4 matrix, could be successfully synthesized on WC-Co substrates by a hybrid coating system of arc ion plating (AIP) and sputtering method. The hardness and Young's modulus value of the Ti-Al-Si-N film increased with incorporation of Si, and had the maximum value of similar to55 GPa and similar to650 GPa at the Si content of 9 at.%, respectively. The average friction coefficient of the Ti-Al-Si-N films largely decreased with an increase of the Si content. This behavior would be attributed to the tribo-chemical reaction between Si and ambient humidity, which enabled to form SiO2 or Si(OH)(2) tribo-layer playing a role as self-lubricant. The harder Ti-Al-Si-N film was found to be more wear-resistant against steel. A systematic work on the microstructure and mechanical properties of Ti-Al-Si-N films is reported in this paper. (C) 2003 Elsevier B.V. All rights reserved.