Effect of vacuum annealing on the microstructure and tribological behavior of hydrogenated amorphous carbon films prepared by magnetron sputtering

Abstract

Hydrogenated amorphous carbon films (a-C:H) were prepared on silicon and steel substrates by medium frequency unbalanced magnetron sputtering with argon (Ar) and methane (CH4) as the source gases. The effect of annealing temperature in vacuum on the microstructure as well as mechanical properties and tribological behavior of as-prepared a-C:H films were investigated. The friction and wear behaviors of the films in different environments (vacuum, N2, and air) were evaluated with a pin-on-disk tribometer; and their sliding lifetime in vacuum was discussed in relation to friction and wear mechanisms. Results show that annealing in vacuum at a low temperature of up to 200 ℃ causes little change in the microstructure and hardness of a-C:H films but reduces their internal stress and surface roughness to some extent. These annealed films exhibit excellent antiwear ability in all test environments and show promising potential as a kind of space lubricants. The film begins to release hydrogen and increases the content of graphite-like structure at about 300 ℃. As a result, a-C:H films annealed above 200 ℃ have increased surface roughness as well as reduced hardness, internal stress, and wear resistance in all test environments.