Synthesis, Microstructural, and Mechano-Tribological Properties of Self-Lubricating W-S-C(H) Thin Films Deposited by Different RF Magnetron Sputtering Procedures

Abstract

Carbon-alloyed transition metal dichalcogenide (TMD) coatings have great potential for providing a good tribological response in diverse operating environments. There are different ways to synthesize these coatings by magnetron sputtering, with no clear indication of the best possible route for potential upscaling. In this study, tungsten-sulfur-carbon (W-S-C) coatings were deposited by radio frequency (RF) magnetron sputtering via four different methods. All coatings were sub-stoichiometric in terms of the S/W ratio, with the bombardment of the growing film with backscattered Ar neutrals being the main mechanism governing the S/W ratio. The crystallinity of the films was dependent on the C and S contents. X-ray photoelectron spectroscopy (XPS) revealed W-S and W-C bonding in all coatings. Raman spectroscopy showed the presence of an a-C phase with predominant sp2 bonding. The hardness of the coatings may be related to the C content and the S/W ratio. A friction coefficient of 0.06–0.08 was achieved during sliding in ambient air by the coatings deposited in non-reactive mode with optimal C contents. The results indicate that sputtering in non-reactive mode should be the method of choice for synthesis of these coatings.

Effect of Annealing Heat Treatment on the Composition, Morphology, Structure and Mechanical Properties of the W-S-N Coatings

“…TMDs show excellent sliding performance in a vacuum and poor performance in ambient atmospheres [14,15]. TMDs have been alloyed with different metals [16][17][18][19][20][21][22][23] and non-metals such as C and N [10,[24][25][26][27][28][29][30][31][32], to improve their sliding efficiencies in diverse environments (ambient air at room temperature, ambient air at elevated temperatures, dry N 2 and vacuum). Until now, the most successful approaches include the alloying of TMDs with non-metals (C and N).…”

“…Considering the market, universal solid lubricants that can present low COF in diverse environments (especially for the aerospace industry) are demanded. In the recent past, our group has reported various studies on the lab-scale and semi-industrial scale optimisations of different TMDs alloyed with C and N [11,[31][32][33][34]. During these studies, the sliding properties of these C-and N-alloyed coatings have been tested in ambient air at both room temperature and elevated temperatures.…”