Tribological properties of MoS 2 coating for ultra-long wear-life and low coefficient of friction combined with additive
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Tribological properties of MoS2 coating for ultra-long wear-life and low coefficient of friction combined with additive g-C3N4 in air Yupeng ZHANG1,3, Panpan LI1,2, Li JI1,2, Xiaohong LIU1,2, Hongqi WAN1,2, Lei CHEN1,2, Hongxuan LI1,2,*, Zhiliang JIN3,* 1
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Science， Lanzhou 730000, China
2
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Science, Beijing 100049, China
3
School of Chemistry and Chemical Engineering, North Minzu University, Yinchuan 750021, China
Received: 21 August 2019 / Revised: 15 January 2020 / Accepted: 16 February 2020
© The author(s) 2020. Abstract: The solid lubricant MoS 2 demonstrates excellent lubricating properties, but it spontaneously oxidizes and absorbs moisture in air, and thus results in poor wear resistance and short wear-life. In this study, the additive g-C3N4 (CN) was successfully combined with MoS2 via hydrothermal synthesis as a solid lubricant for the first time. Meanwhile, a low friction coefficient (COF, μ = 0.031) and ultra-long wear-life of CN/MoS2 compared to pure MoS2 in air were demonstrated. The functional groups and good crystallinity of the lubricant material were characterized via Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The formed valence states in CN/MoS2 were analyzed via X-ray photoelectron spectroscopy (XPS). The characterized results of the scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) show the morphology and interior crystal phase structure of CN/MoS2. From the cross-section analysis, the presence of iron oxide nanoparticles lubricating film is synergistic with CN/MoS2 film during the friction process, resulting in its ultra-long wear-life. In particular, the friction mechanism of interlayer sliding friction combined with energy storage friction was analyzed and proposed. Keywords: solid lubricant; CN/MoS2; friction coefficient (COF); wear-life
1
Introduction
From a tribological perspective, the lubricity and anti-wear of contact materials determine their sliding stability and wear-life [1]. Solid lubricant materials commonly used include graphene, hexagonal boron nitride (HBN), diamond, molybdenum disulfide (MoS2), and polymers [2, 3]. Among these, the well-known lamellar transition metal sulfide MoS 2, equipped with the advantages of thermal stability,
lower shear strength, and strong surface adhesion force, is a good lubricating material [4–6]. The MoS2 atomic-layered structure was formed via the strong covalent bond between Mo and S atoms (S–Mo–S), especially the single-layer MoS2 prepared using chemical vapor deposition or mechanical exfoliation exhibited the feasibility as protective or lubricant layers for micro- and nano-devices, whereas weak van der Waals force between the layers [7–9]. By easy slippage and weak interactions between
* Corresponding authors: Hongxua
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