Friction and wear performance of multilayered a-C:H:Al coatings

• a-C:H:Al films were produced by PECVD/magnetron sputtering in an industrial coater.
• Influence of the rotation of substrates on the coatings properties was studied.
• Rotation of the substrates led to a multilayered structure with 40 nm thick periods.
• The introduction of aluminum in a-C:H led to a significant decrease in friction.
• Rotation of substrates preserved the structural, mechanical and tribological properties.

Hydrogenated amorphous carbon thin films containing aluminum (a-C:H:Al) have been produced by a hybrid technique using plasma enhanced chemical vapor deposition and magnetron sputtering of an aluminum target. Various sputtering powers were used in order to explore different Al/(Al + C) ratios. Two deposition configurations for the substrates were tested: a dynamic and a static. The dynamic mode led to a multilayered structure made of alternating Al-rich and Al-poor layers with a total thickness of about 40 nm for each period. Regardless of the deposition mode, nanoindentation showed that an increase in Al concentration resulted in a decrease in hardness compared to the pure a-C:H coatings. Moreover, the hardness of the dynamic a-C:H:Al films was less affected and seemed to be weighted between the power-equivalent static Al-doped DLC and the pure a-C:H. The results of tribological characterization in dry conditions indicated that the friction coefficient was significantly reduced by the introduction of Al from 0.2 to less than 0.1 for all of the Al-doped films. However, the wear resistance was also affected by the doping. Nevertheless, Al doping compatible with industrial purpose (i.e. dynamic mode) can be considered at moderate sputtering power in order to obtain a-C:H:Al coatings that exhibit low friction coefficient and moderate wear rate in relation with good hardness and H/E ratio.