THE ROLE OF INTERFACIAL FILMS IN THE FRICTION AND WEAR PROPERTIES OF W-CO-C SPUTTERED COATINGS

W-Co-C amorphous coatings with cobalt content between 18 and 30 at.% w ere deposited by r.f. sputtering on M2 (AISI) high-speed steel (HSS) d isks. They were tribologically tested by pin-on-disk against uncoated mild steel pins with a sliding speed of 0.5 m s-1 and normal load of 4 N. Friction coefficients ranged from 0.38 to 0.49. Wear coefficients between 1 and 2 x 10(-15) m(2) N-1 were measured on the coated surface s. Very low wear (2 to 20 x 10(-17) m(2) N-1) was obtained on the stee l pins. This was related to the formation of a transfer film on the un coated surfaces. Transmission electron microscopy analysis of this tra nsfer film revealed the presence of various crystalline phases (WC, W2 C, WC1-x and CoWO4) in addition to amorphous phase. Formation of the t ransfer films is discussed in terms of film composition and stress-ind uced crystallization.