Abstract
Diamond-like carbon (DLC) films directly deposited on rubber substrate is undoubtedly one optimal option to improve the tribological properties due to its ultralow friction, high-hardness as well as good chemical compatibility with rubber. Investigating the relationship between film structure and tribological performance is vital for protecting rubber. In this study it was demonstrated that the etching effect induced by hydrogen incorporation played positive roles in reducing surface roughness of DLC films. In addition, the water contact angle (CA) of DLC-coated nitrile butadiene rubber (NBR) was sensitive to the surface energy and sp2 carbon clustering of DLC films. Most importantly, the optimum tribological performance was obtained at the 29 at% H-containing DLC film coated on NBR, which mainly depended on the following key factors: (1) the DLC film with appropriate roughness matched the counterpart surface; (2) the contact area and surface energy controlled interface adhesive force; (3) the microstructure of DLC films impacted load-bearing capacity; and (4) the generation of graphitic phase acted as a solid lubricant. This understanding may draw inspiration for the fabrication of DLC films on rubber to achieve low friction coefficient.
Highlights
Reducing the friction and wear of dynamic rubber seals can greatly prevent leakage, maintain gas pressure, and exclude dirt, thereby benefiting to energy conservation and environmental protection [1,2,3]
In the mixed working atmosphere of methane (10 sccm, 99.99%) and argon (100 sccm, 99.99%), a buffer layer of thin carbon film was prepared at negative voltage of 800 V for 10 min to guarantee the fine adhesion of Diamond-like carbon (DLC) films with different hydrogen contents on nitrile butadiene rubber (NBR)
The sp2/sp3 ratio in hydrogenated amorphous DLC films can be derived from ID/IG ratio and the G peak position [27]
Summary
Reducing the friction and wear of dynamic rubber seals can greatly prevent leakage, maintain gas pressure, and exclude dirt, thereby benefiting to energy conservation and environmental protection [1,2,3]. The alteration of rubber surface properties such as hydrophobicity and roughness will inevitably lead to the change of friction behavior, which provides an opportunity to govern friction behavior with regard to dynamic rubber seals [8]. A variety of techniques, including chemical and physical techniques, have been developed to modify the rubber surface. Chemical techniques, such as surface halogenation, sulfonation, and oxidation, are often applied to change the compositions on rubber surface [9]. Unlike the carbide and nitride coating that possessed high friction under unlubricated conditions, DLC films show low friction when sliding against most counterpart surfaces. This work explores the governing factor to friction properties of DLC-coated rubber by introducing the hydrogen plasma to manipulate film structures and morphologies, aiming to produce high-performance dynamic rubber seals
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