Structure and Tribological Properties of Medium Frequency Magnetron Sputtered WS_x Films with Different S/W Ratios

WS_x films on Si (100) wafer and 9Cr18 steel substrates were deposited by medium frequency magnetron sputtering. The structure of the films was characterized by X-ray diffraction, field emission scanning electron microscope, atomic force microscope and X-ray photoelectron spectroscope. The mechanical and tribological properties were investigated using triboindenter and vacuum ball-on-disk tribometer, respectively. The results show that the S/W ratio raised with increasing working pressure, and increased firstly and then decreased with increase in sputtering power density, that was ascribed to the different oxidation degree of the deposited films and the selective sputtering. When the S/W ratio was low, the films were compact and hard, but exhibited high friction and wear due to the high content of W. As the S/W ratio was raised, the films showed an increase in WS₂ content, along with a lower and more stable friction and better wear resistance.