Microstructure and Tribological Properties in Atmosphere of WS_x/Ni/a-C/Ni Multilayer Films Deposited by Sputtering

WS_x/Ni/a-C/Ni multilayer films with different Ni layer thicknesses were successfully prepared by alternate depositing WS₂, Ni and amorphous carbon (a-C) layer on silicon substrate with magnetron sputtering technique. The composition and microstructure of the films were investigated by using scanning electron microscopy, X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. The mechanical and tribological properties of the films in air were evaluated by using nano-indentation tester, scratch tester and ball-on-disc tribotester. The results show that the density of WS_x/Ni/a-C/Ni multilayer films decreased and the value of n_s/n_w (the atomic fraction ratio of S to W) dropped from 0.84 to 0.73 as increasing the Ni layer thickness, the WS₂ layer was microcrystalline or amorphous. With the increase of Ni layer thickness, the hardness and wear rate of the multilayer film decreased first and then increased, but the friction coefficient increased from 0.22 to 0.38, the adhesion increased first and then decreased. The multilayer film with Ni layer thickness of 6 nm exhibited the hardness of 13.4 GPa, the excellent antioxidant properties and the best wear resistance, wear rate is 9.47×10^–14 m³/(Nm).