Microstructure And Mechanical Properties Of WS₂/a-C Multilayer Films With Different Modulation Ratios

Due to the layered structure,WS₂ presents the advantages of low friction coefficient,good wear resistance and others in vacuum,and has been widely used in mechanical and aerospace fields.But the single WS₂ film shows loose structure,low hardness,and poor adhesion and is prone to be oxidated and deliquesced in moist atmosphere,which limits its application.Some researches have been made on the multilayer film to improve the lubrication performance of WS₂ films in humid air.It has shown that WS₂/C composite film presents compact morphology and good tribological properties in humid air and multilayer design can alleviate the layer stress and interfacial stress.WS₂/C multilayer films?modulation period ²0 nm?were prepared on silicon substrate by magnetron sputtering WS₂ target and C target.The relationship between modulation ratio?La-C/LWSx=1:39,1:19,1:9,1:6,1:4?and microstructure,mechanical properties of the films deposited at 80? and 200? are discussed;the tribological properties of the films deposited at different temperatures and different modulation ratios in vacuum and in air?RH?50%?are investigated.As for the films deposited at 200?,the test results show that,with the increase of modulation ratio,the S/W ratio of multilayer films is in the range of 0.88⁰.98,the film presents compact structure and more smooth surface,the WSx sublayer is defined as crystallite and the WC phase is found at the interface between WSx sublayer and a-C sublayer;the hardness of the films monotonously increases from 7.8 GPa to 9 GPa,the film tensile stress decreases first and then increases,the adhesive strength decreases and reaches the maxmium at La-C/LWSx of 1:39.In the air,the friction coefficient of multilayer film shows a trend of increase,and is higher than that of single WSx,the wear rate presents increases monotonically,when La-C/LWSx is less,the wear rate is lower than that of single WSx.When La-C/LWSx is 1:39,the friction coefficient is 0.174 and the wear rate is 6.1×10-15 m3N-1m-1,and the film presents the best tribological properties.In vacuum,the friction coefficient of multilayer film also shows an increasing tendency,and higher than that of single WSx,the wear rate increases monotonically,when La-C/LWSx is less,the wear rate is lower than that of single WSx.The minimum friction coefficient of 0.06 is reached at La-C/LWSx of 1:19 while the minimum wear rate of 2.2×10-15 m3N-1m-1 occurs at La-C/LWSx of 1:19,the film shows the best tribology.As for the films deposited at 80?,with the modulation ratio increasing,the films also present smooth surface and compact structure,the S/W ratio is in the range of 1.01¹.27,slightly higher than the films deposited in elevated temperature;the WSx sublayer is also defined as crystallite while the WC phase is absent at the interface between WSx sublayer and a-C sublayer;the hardness on the whole shows a trend of increase and runs up t o 7.87 GPa,the adhesive strength monotonically decreases,the maximum of 37 N occures at La-C/LWSx of 1:39.Both in the air and in vacuum,the friction coefficient of the films shows decreases first and then increases,and reaches the minimum at La-C/LWSx of 1:19,the wear rate of the films exhibits monotonically increases,when La-C/LWSx is 1:39,the wear rate is 3.66×10-15 m3N-1m-1 in air while in vacuum is 0.237×10-16 m3N-1m-1,the film shows best wear resistance.