Tribological behavior of plasma-enhanced CVD a-C:H films. Part II: multinanolayers

The tribological behavior of multinanolayered amorphous hydrogenated carbon (a-C:H) films was investigated. The multilayered films were synthesized by depositing soft/hard a-C:H alternating nanolayers, using dc plasma-enhanced CVD in a CH4/Ar discharge. The soft and hard nanolayer components were produced by changing the CH4/Ar ratio. Multilayered films with the same or variable thickness of the soft and hard nanolayer were synthesized. The mechanical properties were studied by nanoindentation, intrinsic stresses by profilometry and tribological behavior by pin-on disk experiments. In general, the multilayered films exhibited lower intrinsic stresses, higher hardness and elastic modulus than the respected average values of their two constituent films. Furthermore, the multilayers were found to possess both, low friction and high wear resistance. The tribological properties were enhanced by decreasing interlayer thickness with the 50 nm/50 nm multinanolayered film exhibiting the best tribological performance. This behavior is attributed to a correlation between the thickness of the nanolayer constituent and properties of the transfer layer.