Nanostructured Cr-WS2 Solid Lubricant Coating for Space Applications

Abstract

Abstract Tungsten disulphide (WS2) is one of the widely used intrinsic low friction materials, which is commonly used in the form of coating. WS2 offers very low coefficient of friction only in non humid conditions. Presence of humidity destroys this property and restricts its utility. Modifying the structure of WS2 by adding certain metals helps in overcoming this limitation and in addition improves the mechanical properties. Further, deposition technique and processing parameters play a critical role in deciding the properties of a coating. In this work, Cr-WS2 coatings were deposited on silicon and stainless steel substrates using a fourcathode direct current (DC) unbalanced magnetron sputtering system. Effect of substrate bias and WS2 top layer on the lubricating behavior of coatings has been studied. Deposited coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), nanoindentation, and tribometry techniques to analyze the structure, morphology, mechanical and tribological properties. Optimized coating showed a sharp reflection from (101) hexagonal WS2 phase along with broad (002) and (103) reflections, which signifies a combination of nanocrystalline and amorphous behavior. Surface morphology of the coating revealed typical acicular features along with small clusters of cauliflower-like microstructure. For the coating without top WS2 layer, only cauliflower-like features were observed. It has been found that the applied substrate bias significantly affects the lubricating properties. The coating which consists of top WS2 layer deposited at zero bias voltage exhibited the best lubricating properties with co-efficient of friction (COF) of 0.07 till 1300 cycles and an average value of 0.10 till 1800 cycles for the tests conducted in ambient air atmosphere.

Keywords: Magnetron sputtering, solid lubricant coating, Cr-WS2, Co-efficient of friction

Cite this Article: M. Jeevitha, Srinivas G., Praveen Kumar V., Jakeer Khan G.H., Siju, K. Niranjan, Harish C. Barshilia. Nanostructured CrWS2 Solid Lubricant Coating for Space Applications. Journal of Instrumentation Technology & Innovations. 2019; 9(1), 12– 18p