Nanostructured Au-WS2 solid lubricant coatings prepared by magnetron sputtering

Deepthi, B and Siju, John and Srinivas, G and Praveen, Kumar and Jakeer, Khan and Barshilia, Harish C (2011) Nanostructured Au-WS2 solid lubricant coatings prepared by magnetron sputtering. In: National Conference on Chemistry of Materials (NCCM-2011), September 28, 2011, Tumkur University. (Unpublished)

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Low friction applications in space and aerospace sectors have attracted the use of solid lubricants which overcome the limitations of liquid lubricants in extreme environments and facilitate dry lubrication. Solid lubricant coatings of transition metal dichalcogenides such as MoS2 and WS2 have been studied extensively since they provide low friction under high vacuum conditions and inert gas environments. In order to extend their use in ambient conditions, metal doped transition metal dichalcogenides have been explored. In the present study, Au-WS2 nanocomposite coatings (approximately 2 m thick) were prepared with 60 at.% Au by magnetron sputtering using high purity Au and WS2 targets. Structural characterization of the coatings using X-ray diffraction indicated the presence of (111), (200) and (220) peaks of cubic Au and broad bands corresponding to (002) and (004) planes of hexagonal WS2. Surface morphology of Au-WS2 coatings was studied using field emission scanning electron microscopy (FESEM) and atomic force microscopy which showed formation of uniformly distributed interconnected ligament-like features. X-ray photoelectron spectroscopy data indicated the presence of metallic Au, and W in the form of WS2 and some amount of WO3. Transmission electron microscopy (TEM) studies showed the presence of a two phase nanocomposite structure that resulted in regions of high and low electron intensity and the two phases were uniformly distributed in the coating. The ring pattern with a halo in the electron diffraction data of Au-WS2 coating confirmed the presence of nanocrystalline and amorphous phases in the coating. High resolution TEM studies confirmed that nanocrystalline Au was dispersed in a matrix of nanocrystalline and amorphous WS2. The electrical resistivity of Au-WS2 coating measured using four-point-probe method was approximately 0.2 m compared to Au and WS2 coatings which exhibited electrical resistivity values of approximately 0.04 m and 0.057 m, respectively. Ball-on-disc reciprocating wear tests were carried out using a 4 mm diameter WC ball in air at 60% relative humidity to study the wear behavior. Au-WS2 coating exhibited a friction coefficient of approximately 0.22 after 57,600 cycles at a load of 7 N whereas, WS2 coating showed friction coefficient of 0.36. Analyses of the ball and wear tracks using FESEM at the end of the wear test indicated formation of smooth transfer films, less accumulation of wear debris and reduced oxidation in the case of Au-WS2 coatings whereas WS2 coatings exhibited formation of brittle cracks, accumulation of large amount of wear debris and severe oxidation. Therefore, Au-WS2 nanocomposite coatings clearly perform better than WS2 coatings in terms of frictional stability over a long duration and have great potential for solid lubricant applications in ambient conditions. Further, the excellent electrical conductivity of Au-WS2 nanocomposite coatings compared to WS2 coatings makes them suitable for electrical contact applications.

Item Type: Conference or Workshop Item (Paper)
Subjects: CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
Depositing User: Dr. Harish C. Barshilia
Date Deposited: 06 Jan 2012 05:13
Last Modified: 06 Jan 2012 05:13

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