Conductive and tribological properties of TiN-Ag composite coatings under grease lubrication
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Conductive and tribological properties of TiN–Ag composite coatings under grease lubrication Feihu LIN, Yanqiu XIA*, Xin FENG School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China Received: 26 September 2019 / Revised: 15 November 2019 / Accepted: 16 February 2020
© The author(s) 2020. Abstract: TiN–Ag composite coatings were prepared by pulsed bias arc ion plating. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) were applied to analyze the compositions of the coatings. Tribological properties of the coatings were studied using an MFT-R4000 ball-on-disk friction tester in the presence of lubricating greases containing multilayer graphene. Scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to analyze the worn surface compositions of the lubricating films. The results show that with the decrease in Ag in the film, hardness increased but electrical conductivity decreased. The coating with 10 at% Ag content shows the best friction-reducing and anti-wear properties, which can be attributed to the moderate content of Ag embedded in the TiN crystal gap that enhanced the grain bonding force to improve the anti-wear and self-lubricating ability. Graphene can be adsorbed on the coating as a solid lubricant. Keywords: silver; tribology; contact resistance; lubricating grease
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Introduction
Owing to the rapid development of technology, electrical contacts are ubiquitous in various devices [1]. In a power and signal transmission system, the reliability, stability, accuracy, and service life of the system depend on the electrical contact materials [2, 3]. Most of the electrical contacts are permanent connections, however, the relative motion of the contacts still occur owing to changing vibrations and temperatures because of the different thermal expansion coefficients of the electrical contacts [4–6]. Researchers have focused on the electrical conductivity and wear resistance of sliding contact components. However, the wear process between electric contacts is much more complicated when current-carrying occurs because it is not only affected by mechanical factors, such as hardness and roughness, but also
by current-thermal effects and operating conditions. In terms of tribology, the lubrication and wear resistance of electrical contact materials are two important factors that determine the long-term stable operation of sliding connections [7, 8]. When current carrying occurs, the heat caused by the combination of current-thermal effects and friction can significantly damage the contact pair, resulting in increased friction coefficient (COF) and wear rate [9]. Ag-based materials exhibit high conductivity, selflubricating, anti-oxidation, anti-sulfuration, and antifusion welding properties. However, owing to high temperature and its low hardness, the Ag layer suffers from severe wear, plastic deformation, and surface oxidation during the cur
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