Tribological behaviour of diamond coatings obtained by combustion flame process

The friction and wear behaviour of diamond coatings have been investigated by several authors. The studied diamond coatings were mainly produced by CVD assisted by microwave, hot filament and Radio Frequency techniques (hydrogen dominated system). The dangling bonds of the carbon atoms on the surface of these films are terminated by hydrogen. This paper presents a study of the friction behaviour of diamond coatings produced by combustion flame method (oxygen dominated system). In that case, the surface of these films is terminated by oxygen. Various types of diamond coatings were deposited on carbide tungsten pins sliding against aluminium, copper, HSS steel and XC48 steel rotating discs. The friction experiments were conducted in vacuum and under active gaseous species, such as molecular oxygen, hydrogen and water vapour. The experimental results show that their friction coefficient is strongly affected by gaseous environment. Under vacuum, when the surface of the coating is terminated by oxygen, the friction coefficient is lower than the one obtained in gaseous environment and in ambient air. Machining tests realised with the different diamond coated discs have also been carried out. Results obtained with high rates of diamond deposition encourage to apply these films to cutting tools.