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Enhancement in the tribological performance of WSx/a-C multilayer films with Al sublayers in vacuum

The manufacturing of multilayer films with improved mechanical and tribological properties has attracted attention recently for enabling their space applications. In this study, we aim to optimize the manufacturing process of WSx/a-C multilayer films by alternately depositing WS2, amorphous carbon (a-C), and Al metal on silicon substrates through magnetron sputtering. The microstructure and morphology of the multilayer films were investigated by x-ray diffractometry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The mechanical and tribological properties of the films were evaluated in vacuum using a nanoindentation tester, ball-on-disk tribometer, and scratch tester. The results showed that the addition of an Al layer with an optimal thickness refined the microstructure of the films. The tribological properties of the films deteriorated with increasing thickness of the Al single layer. When the thickness of the Al film was 1 nm, the tribological properties of the films were optimal, and the adhesion was maximum (49.1 N). Hardness of the films gradually decreased with an increase in the thickness. Wear rate of the films decreased initially and then increased, and the wear rate was lowest when the thickness of the Al single layer was 2 nm (1.41 × 10−15 m3 N−1 m−1). By manufacturing films with optimal thickness, suitable tribological properties for vacuum applications can be achieved.