TRIBOLOGICAL PROPERTIES AND CHARACTERIZATION OF DIAMOND-LIKE CARBON COATINGS WITH SILICON PREPARED BY PLASMA-ASSISTED CHEMICAL VAPOR-DEPOSITION

Amorphous C-Si coatings containing hydrogen (a-C-Si-H) were formed by a d.c. glow discharge method from reactant gases of CH4, SiCl4, H2, and argon. Coatings with a smooth surface, a hardness of HV 2000 and adhesion to steel substrates were obtained below 550-degrees-C at a deposition rate of 1-4-mu-m h-1. The ball-on-disk test, against steel with no lubricant in ambient atmosphere, revealed that the friction coefficient-mu of the a-C-Si-H coatings changed markedly with the carbon content. Mu-abruptly decreased from 0.43 to 0.16 at around 60 at.% C (composition excluding hydrogen) and reached a minimum value as low as 0.04 in a range of about 75-85 at.% C content. Laser Raman spectroscopy indicated that the low-friction a-C-Si-H coatings consisted of diamond-like carbon with silicon (DLC-Si). The mu-value of 0.04 was below one-third that of DLC coatings without silicon, where mu = 0.12-0.20. The wear of both the DLC-Si and the counter steel ball was very small.