High throughput deposition of hydrogenated amorphous carbon coatings on rubber with expanding thermal plasma

Flexible hydrogenated amorphous carbon (a-C:H) thin film coated on rubbers has shown outstanding protection of rubber seals from friction and wear. This work concentrates on the potential advances of expanding thermal plasma (ETP) process for a high throughput deposition of a-C:H thin films in Ar/C2H2 plasma on nitrile butadiene rubber (NBR). The effect of the arc current on the microstructure, interfacial adhesion and tribological properties of the deposited a-C:H films on NBR is scrutinized. The temperature variation during the short ETP process is small and only yields sub-millimeter segmented a-C:H films, in consistence with a previously developed model. Increasing the arc current from 30 A to 75 A leads to smaller sizes of film patches (reduced from 940 µm to 125 µm), enhanced adhesion strength from 20.4 MPa to 91.8 MPa and higher hardness (from 5.5 GPa to 8.9 GPa) of the deposited a-C:H films on rubber. The tribological performance of the ETP a-C:H coated NBR is a compromise between the adhesion strength and hardness of the a-C:H films, with the coefficient of friction being reduced from about 1 (uncoated NBR rubber) to less than 0.25 of a-C:H film coated NBR.