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

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.