Synthesis and characterization of titanium-containing graphite-like carbon films with low internal stress and superior tribological properties

Abstract

Titanium-containing graphite-like carbon films were deposited on silicon substrates by an unbalanced magnetron sputtering system. The effect of titanium concentration on the film microstructure and properties was subsequently investigated by means of different characterization techniques. It is found that the current carbon films have a graphite-like structure with some fine titanium carbide particles dispersed in an amorphous carbon matrix. With increasing titanium concentration from 0 at% to ∼9.6 at%, the sp2 concentration in the film shows a slight increase, while the hardness of the carbon films decreases evidently when a small quantity of titanium (∼2.9 at%) is introduced into the film structure, but it does not suffer an obvious change with further increase in titanium concentration until the titanium concentration is up to ∼9.6 at%. The increased hardness of the film with a titanium concentration of about 9.6 at% is probably due to the formation of specified dimension titanium carbide crystals in the amorphous carbon matrix. All the current carbon films have low internal stress and rough surface, and the doping of titanium has little influence on their internal stress and root mean square roughness. The friction coefficient of the films decreases distinctly as the titanium concentration increases from 0 at% to ∼9.6 at%, but the wear rate does not increase evidently until the titanium concentration exceeds over ∼6.2 at% in air tests. The titanium-containing graphite-like carbon films show a stable friction coefficient and extremely low wear under oil lubricated conditions. The unique graphite-like structure, the high hardness and elastic modulus ratio (H/E) and the easy formation of a transfer film are mainly responsible for the superior tribological properties of the resulting titanium-containing graphite-like carbon films.