Sputter deposited nanostructured Au-WS2 solid lubricant coatings

Au-WS2 nanocomposite coatings with approximately 60 at.% Au were prepared using magnetron sputtering from 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. High resolution transmission electron microscopy studies showed the presence of a two phase nanocomposite structure wherein 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 mu Omega m compared to Au and WS2 coatings which exhibited electrical resistivity values of approximately 0.04 mu Omega m and 0.057 Omega m, respectively. Ball-on-disc reciprocating tests at a load of 7 N showed that Au-WS2 nanocomposite coating exhibited a friction coefficient of 0.22 after 57,600 cycles and outperformed Au and WS2 coatings. Analyses of the ball and wear track of Au-WS2 coating using FESEM at the end of the wear test indicated formation of smooth transfer films, less accumulation of wear debris and reduced oxidation.