Effect of Rubber Surface Roughness on the Tribological Properties of DLC Film

Rubber have usually been used as seals to prevent lubricant leakage and contaminants from entering the machine. However, rubber seals can easily fail under harsh conditions, resulting in fluid leakage or intrusion of contaminants into the lubricant. Depositing DLC carbon-based films on rubber surfaces can extend rubber life and enhance its wear resistance. In this paper, the effect of surface roughness of Ethylene Propylene Diene Monomer (EPDM) rubber on the microstructure, adhesion and tribological properties of DLC film and Cr/DLC film was investigated, and the effect of Cr interlayer on the DLC film on the rubber surface was clarified. The EPDM rubbers were cut into 30 mm × 25 mm rectangular blocks, and they were sanded with different types of sandpaper to obtain new rubber substrates with an average surface roughness of 3 600 nm, 2 300 nm, 1 100 nm and 900 nm, respectively. These rubber substrates were cleaned using a hot soap solution and distilled water to remove dust. Subsequently, DLC and Cr/DLC films were deposited on the rubber substrates with different roughness by unbalanced magnetron sputtering. The substrates were etched with Ar plasma to remove the oxides on the surface of the samples before depositing the films at a bias voltage of ‒300 V, the etching time of 15 min. Subsequently, the Cr interlayer with a thickness of about 200 nm was deposited on the surface of the sample with a Cr target current of 3 A and deposition time of 12 min. Finally, the DLC layer was deposited with a deposition current of 3.5 A and a deposition time of 2 h. The surface roughness of the substrates and DLC films were obtained by a two-dimensional profiler. Scanning electron microscope and Raman spectroscopy were used to characterize the surface morphology and structural composition of the film. The adhesion force, tribology and wear resistance of DLC film were evaluated by the X-cut test and the friction and wear test respectively. The surface roughness of the substrate had no significant effect on the microstructure of the film, but had a greater impact on the film adhesion and tribological properties. The film adhesion initially increased and then decreased with the increase of the substrate roughness. When the roughness of the substrate was smaller, the locking effect between the film and the substrate was weakened due to the smoother rubber substrate. When the substrate was larger, the surface of the rubber substrate was damaged, resulting in uneven distribution of stress on the rubber surface and concentrated in the raised parts, the film was easy to peel off. When the substrate surface roughness was 1 100 nm, the DLC film had the strongest adhesion and the best tribological properties. Moreover, the introduction of the Cr interlayer played a positive role in improving the film adhesion and load-bearing capacity. An appropriate increase in substrate surface roughness can enhance the adhesion of DLC film and improve the tribological properties of the film. The Cr interlayer can improve the load-bearing capacity of the film, thereby improving the wear resistance of the film. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.