Effect of local pressure difference caused by argon flow on properties of DLC films on rubber

Abstract

The application of a diamondlike carbon (DLC) coating on rubber surfaces is a promising method to enhance the tribological properties of rubber and alleviate its poor wear resistance. However, in the preparation of DLC films, accurate pressure detection in the sputtering region is challenging due to the single detection position in common sputtering systems. In this paper, the direct current magnetic sputtering method was used to prepare DLC films on nitrile butadiene rubber (NBR). A set of Faraday beam detection device (FBDD) was employed to monitor the current density in the sputtering region. It was found that even if the pressure at the detection position of the vacuum gauge is consistent, the actual pressure in the sputtering region may be different under different rates of argon flow based on the detection results from the FBDD. The surface energy of DLC films was also calculated and researched. According to the results of FBDD, a series of analytical characterization methods were selected to explore the influence mechanism of changing the Ar flow rate on the properties of DLC films on NBR when the initial sputtering pressure remained consistent. The results of FBDD show that the density of the beam in the sputtering region increases with the increase in the Ar flow rate introduced into the vacuum chamber. The surface energy of DLC films was also calculated and evaluated by a contact angle tester. Raman and x-ray photoelectron spectroscopy results indicate that the increase in the Ar flow rate leads to an increase in pressure, which is conducive to the formation of sp3 in DLC films, and the increase in sp3 improves the surface energy of DLC films. The highest sp3 content and surface energy among as-prepared DLC films are observed when the argon flow rate was 40 SCCM. Ball-on disk friction experiment was used to characterize the tribological performance of DLC films on NBR rubber and the adhesion between DLC films and NBR rubber was evaluated by a nanoscratching test. Combining the results of tribology and nanoscratching testing, it can be inferred that the Ar flow rate plays an important role in improving the mechanical properties of DLC films on NBR rubber. Furthermore, the results of scanning electron microscopy confirmed that the sputtering atoms can effectively fill in the grooves of the rubber substrate. This finding is of significance for controlling the sputtering process of preparing DLC on rubber and improving the frictional properties of rubber.