Tribological behavior of O2 and CF4 plasma post-treated diamond-like carbon films under dry air and in a high relative humidity environment

•Influences of plasma treatment on tribological properties in different environments.•The tribochemical effects on friction and wear mechanism.•The passivation of plasma molecules to the free σ-bonds of surface carbon atoms.•Considerable differences on the accumulated debris and wear scar.

In this article, the results obtained from a study of the plasma post-treatment of diamond-like carbon (DLC) films using O2 and CF4 plasma are reported. The friction and wear behaviors of the films in dry air and a high relative humidity environment were characterized using ball-on-disk friction testing and an optical microscope. The results indicated that both O2 and CF4 plasma post-treatments of DLC films had strong influences on the friction coefficient measured under dry air, which were compared with the result of the as-deposited DLC film. This effect was due to the passivation of free σ-carbon bonds with hydroxyl (OH) and fluorinated (F) groups on the unoxidized surfaces of the DLC films. Furthermore, the O2 plasma post-treated DLC films exhibited the lowest specific wear rates both in dry air and at high relative humidity, as evidenced by their small wear scars. Therefore, O2 plasma post-treatment can be considered beneficial for improving tribological performance.