Optimizing the Microstructure, Mechanical, and Tribological Properties of Si-DLC Coatings on NBR Rubber for Its Potential Applications

Guangqiao Liu,Bin Zhang,Li Qiang,Zhenlu Wang,Limei Dong,Zedong Wen,Kui Chen

doi:10.3390/coatings10070671

Abstract

Si doped diamond-like carbon (Si-DLC) films were deposited on nitrile-butadiene rubber (NBR), and the effects of deposition parameters on the mechanical and tribological properties of an Si-DLC top layer on NBR were investigated. Then, the sample with the best performance is selected to investigate its tribological behaviors and mechanism under different contact loads. The results show that the growth rate and the doped Si content are also decreased with increasing the CH4 flow rate. The Si atom exists in the form of Si-C bonds at low CH4 flow rate (≤40 sccm) and Si-C + Si-O-C bonds at high CH4 flow rate (≥60 sccm). Furthermore, the sp3 content increases monotonously, while the hardness and H3/E2 ratio firstly decreases and then increases. As a result, the friction and wear behaviors are in line with the change trend of the hardness. The lowest friction coefficient (~0.19) and a slight wear were achieved for the Si-DLC3 film under the relatively high load of 3 N. The tribological results indicate that the friction coefficient and wear increase monotonously with the increase of load, which is mainly attributed to the brittle fragmentation of films at a higher load, and thus a high strength and super toughness DLC films should be needed. Furthermore, the friction and wear behaviors of samples depend critically on its surface topography, and the wear is lower when the friction direction is parallel to the stripes.

Highlights

Nitrile-butadiene rubber (NBR) seals are subject to high friction and wear due to its adhesion-prone to the harder counterpart at a relatively high load, which lead to the loss of its function and failure of the sealing system
Martinez-Martinez et al [37] found that the crack density is directly related to the temperature difference (∆T) from the beginning to the end of deposition, and the larger the temperature difference (|∆T|) means the larger the crack density. This result indicates that the temperature difference of the films deposited at high CH4 flow rates is relatively smaller than that deposited at low CH4 flow rates, and the reasons will be discussed in more detail in the following
Si interlayer/Si doped diamond-like carbon (Si-Diamond-like carbon (DLC)) films were prepared on NBRs, and the influence of CH4 flow rate on the hardness, adhesion, and tribological behaviors of films on NBR were studied systematically, and the sample with the best performance is selected to investigate its tribological behaviors and mechanism under the different contact loads

Summary

Introduction

Nitrile-butadiene rubber (NBR) seals are subject to high friction and wear due to its adhesion-prone to the harder counterpart (ceramic, steel, etc.) at a relatively high load, which lead to the loss of its function and failure of the sealing system. Considering that the friction and wear always occur on the surface and subsurface of materials, and the surface coatings with excellent friction and wear have been suggested as protective coatings. Diamond-like carbon (DLC) film is popularly regarded as a promising protective coating because of their outstanding mechanical and tribological properties such as high hardness, low friction coefficient and high wear resistance [1,2,3,4,5,6]. Nakahigashi et al [7] claimed that a new flexible film has been applied to the rubber o-rings for zoom cameras.

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