Microstructure and tribological properties of pulsed laser deposited WSx/a-C composite films

Abstract:

WSx/a-C composite films with various carbon contents were prepared on monocrystalline silicon substrate by ablating a set of graphite/WS₂ combined targets with pulsed excimer laser. The composition, morphology, microstructure and chemical state of the films were characterized by energy disperse spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The hardness, adhesion to substrate and tribological properties in air (RH=50~55%) of the films were evaluated by nano-indentation, scratch tester and ball-on-disk tribometer. The results show that the S/W ratio maintains a constant value about 2.0 and a WS₂ phase with (002) preferred orientation is formed in the films. With increasing carbon content, the hardness peaks at 36.1%C, the adhesion increases and a maximum value is reached at 52.4%C, the friction coefficient decreases first and then increases and a minimum value 0.144 is reached at 41.2%C. The wear rate varies in the range of (0.91~1.61) ×10_-15 m₃N_-1m_-1 and the film with 36.1%C shows the best wear resistance.

Key words:WS₂; a-C; composite film; mechanical properties; pulsed laser deposition