Effect of substrate rotational speed during deposition on the microstructure, mechanical and tribological properties of a-C:Ta coatings

Rotational speed has an important influence on the performance of coating materials. The a-C:Ta composite coatings were prepared by controlling the substrate rotational speed during deposition process using PVD technique. The results showed that the coating transformed from dense structure to columnar structure. Due to the changes of deposition time and the vapor incident angle of the sputtering ions, the sp2 hybrid structure increased and the C-Ta bonds contents decreased as a function of the rotational speed, which led to the improvement of adhesion force. The average friction coefficient of the composite coatings did not fluctuate significantly for the amorphous carbon matrix and the transfer films formed during friction, while the wear rates were gradually increased. The sample at 0.5 rpm possessed the lowest wear rate, which was mainly associated with the cooperative behavior of the dense structure and the formation of TaC nanoclusters in the composite coating.