Effect of environment on friction and wear properties of diamond-like carbon film

Abstract

Tribological properties of diamond-like carbon (DLC) film were evaluated using a ball-on-disk tribometer in various environments (dry air, O 2, N 2 and vacuum). The DLC film was prepared on Si wafer by a plasma chemical vapor deposition (CVD) system using benzene. When tested in N 2, O 2, dry-air and vacuum environments, the DLC film showed significantly different friction and wear behavior. The lowest friction coefficient (0.06) and wear rate (2.2×10 −9 mm 3/Nm) was observed in N 2 environment, whereas the highest friction coefficient (0.17) and excellent wear resistance (1.7×10 −9 mm 3/Nm) was observed in vacuum, and the lowest wear resistance (5.2×10 −7 mm 3/Nm) in O 2 environment. Tribological properties of the DLC film were dependent on the formation of transfer layer and occurrence of tribo-chemical reactions that were mainly affected by the environment. In a vacuum, there was no transfer layer on the counterpart SiC ball or tribo-chemical reaction, resulting in the DLC film with high friction coefficient and low wear rate. However, in N 2 atmosphere the transfer layer on the counter-part ball was formed, resulting in an excellent friction coefficient and wear resistance. The active gas O 2 would appear to induce a tribo-chemical reaction on the surface of the wear track, resulting in a DLC film with low wear resistance.