Component selection and nano-structuring of WS2/MoS2/a-C thin-film coatings for effective friction reduction in difficult conditions of sliding

Abstract

The possibility of forming new solid-lubricating thin-film coatings consisting of nanosized layers of WS2, MoS2 and amorphous carbon (a-C) with improved antifriction properties has been studied. To control the tribological properties of coatings, the conditions for obtaining layers of 2Н-WS2 and 2Н-MoS2 with a thickness of 5 – 20 nm with a crystalline laminar structure with a basal orientation to the substrate were determined. Nanolayers were created by reactive pulsed laser deposition from metal and metal oxide targets in hydrogen sulfide at elevated temperatures. It is shown that when alternating the processes of selected films deposition, no noticeable solid-phase reactions were observed at the interfaces. Tribological tests were carried out at room temperature using the method of sliding a steel ball over a coated disk without lubrication in an atmosphere enriched with nitrogen (~ 9 % relative humidity). The structural state of the coatings before and after the tribotests was studied by Raman spectroscopy. The lowest friction coefficient ~ 0,015 was found for the WS2 coatings deposited at 500 °C. The tribological properties of the MoS2 coatings turned out to be much worse. The coating, consisting of the WS2 and carbon nanolayers, showed a slightly higher friction coefficient (0,021), but it had the enhanced wear resistance.