Nanocrystalline WC and nanocomposite WC/a-C:H coatings were deposited using pulsed reactive magnetron sputtering of tungsten target under argon/acetylene atmosphere on steel substrates held at a temperature below 423 K. In the range of carbon content of 40-45 at.%, formation of WC chemical bonding and nanocrystalline cubic beta-WC1-x structure was observed. Coatings containing more than 48 at.% of carbon have a two phase nanocomposite structure, composed of nanocrystalline beta-WC1-x grains dispersed in an amorphous carbon (a-C:H) matrix. Nanocrystalline WC coatings show hardness in the range of 36-41 GPa. The hardness of nanocomposite WC/a-C:H coatings decreases continuously from 32 to 15 GPa as the carbon content increases from 48 to approximately 90 at.%, respectively. WC/a-C:H nanocomposites show higher fracture toughness than nanocrystalline WC coatings. The lowest friction coefficient (f less than or equal to 0.1) and high wear resistance (k(vc) <2X10(-7) mm(3) N-1 m(-1)) was achieved by coatings containing approximately 90 at.% of carbon. (C) 2003 Elsevier Science B.V. All rights reserved.