The influence of sputtering procedure on nanoindentation and nanoscratch behaviour of W-S-C film

Sulphides of tungsten with its lamellar structure - whereby weak van der Waals forces act between the layers - are commonly believed to be responsible for their excellent self-lubricating properties. The present investigation is undertaken in order to explore the possibility of using this film for MEMS application. In order to achieve this objective, W-S-C films are deposited on 100Cr6 steel using radio frequency magnetron sputtering. Carbon was incorporated in the films via three different ways: (1) using a reactive gas (CH4), (2) by co-sputtering from separate targets (WS2 and C targets) and, (3) by co-sputtering from a C target embedded with WS2 pellets. Microstructural features and mechanical properties of these films are evaluated with the help of scanning electron microscopy and nanoindentation. The topography, structural features and scratch behaviour are analysed using atomic force microscopy, X-ray diffraction and nanoindenter. It is noted that the film deposited by sputtering two targets exhibits the highest hardness due to high oxygen content. The highest elastic modulus pertains to the film deposited from the carbon target containing WS2 pellets as this film has amorphous structure and the minimum porosity. The friction coefficient under scratching is the highest for reactively sputtered film whereas it is the minimum for the film deposited from the carbon target containing WS2 pellets as this film has amorphous structure and the minimum roughness.