On the S/W stoichiometry and triboperformance of WSxC(H) coatings deposited by magnetron sputtering

WSxC(H) coatings were deposited on single crystal silicon(100) wafers by magnetron co-sputtering and reactive sputtering at various target-substrate distances. Upon increasing the distance, the stoichiometric S/W ratio increases from 0.51 to 1.89. Also, the porosity of coatings gradually augments and a columnar microstructure tends to form. Preferential sulfur resputtering rather than contaminations primarily accounts for the low S/W ratio. TEM reveals randomly oriented WS2(002) platelets in the WSxC coatings when deposited at a large distance, which is supported by XRD. The composite coatings exhibit a decreasing hardness and elastic modulus with increasing target-substrate distance. The triboperformance is strongly affected by the coating composition, the target-substrate distance and the testing environment. Cross-sectional TEM of formed tribofilms reveals an obvious reorientation of WS2(002) basal planes parallel to the plane of sliding, leading to an ultralow friction.