Structural, mechanical and tribological properties of WS2-Ti composite coating with and without hard under layer of TiN

Abstract

The present work reports on the structural, mechanical and tribological properties of WS2 and WS2-Ti composite coating with and without hard under layer of TiN. Pulsed DC closed field unbalanced magnetron sputtering was employed for deposition of the films. The films were characterised with energy dispersive X-ray microanalysis (EDX), grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scratch adhesion test, nanoindentation test and pin-on-disc tribological test. The GIXRD spectrum for WS2 film showed prominent orientation of (002) basal plane parallel to the substrate which was also supported by its morphology showing a fine granular structure. Addition of around 13at.% Ti to the WS2 matrix induced turbostratic stacking of the 10 L (L=0, 1, 2,…) planes, however, the (002) orientation was retained. The film’s hardness, adhesion to the substrate, as well as the tribological properties improved with Ti addition. Addition of a hard under layer of TiN resulted in a denser top WS2-Ti layer because of enhanced nucleation promoted by structural defects of the hard under layer. The tribological performance of the top WS2-Ti layer also improved on TiN under layer addition because of the enhanced load bearing capacity of the top layer.