Study Of Preparation,Structure And Tribological Properties Of MoS₂ Based Composite Films

Over the past years,there was increasing demand for solid lubrication materials in space area alongside the development of science and technology,especially the rapid development of technology and the needs of aerospace technology.As a solid lubricant,MoS2 film plays a significant role in target application of friction mitigation in space,especially in strict requirements of special conditions such as high speed,high load,high/low temperature,high vacuum and space radiation and many other conditions.MoS2 has good tribological performance in vacuum and inert environment owing to its layered structure.But it was easily oxidized and affected the tribological performance when exposed to the air.Therefore,it is of great significance in improving the tribological and wear performance of MoS2 film test in humidity environment.In order to improve the friction and wear properties of MoS2 film in humid conditions,the Mo-S-C,Mo-S-N and Mo-S-C-N composite films were prepared by magnetron sputtering,the pure MoS2 film was prepared as the contrast.The composition,microstructure and morphology of the composite films were investigated with energy-dispersive X-ray spectroscopy(EDS),X-ray diffractometer(XRD),Raman spectrometer,X-ray photoelectron spectroscopy(XPS),scanning electron microscope(SEM),high-resolution transmission electron microscope(HRTEM).The mechanical and tribological properties of the films were analyzed by nanoindentation and ball-on-disk friction tester.The results were as follows:The Mo-S-C composite films were synthesized by r.f.sputtering of MoS2 and graphitetargets,and the influence of C dopant on the structure,morphology,mechanical and the tribological properties of composite films in vacuum,ambient air and mutually alternated atmospheres were discussed in detail.The results show that increasing the sputtering power applied on graphite target from 0 to 400 W,the crystallinity of MoS2 decreased gradually,and the structure of the film was compact.What's more,the film hardness increases significantly by one order of magnitude and the optimized lubricant performance were obtained at 300 W.The friction coefficient of the composite film was stable at 0.04~0.07,and varied from 0.05 to 0.25 in the ambient air atmosphere.The results also reveal that the adaptive release of non-lubricant phase from tribofilm is a critical issue for determining the tribological performance of Mo-S-C composite films in different sliding atmospheres.More interestingly,the lubricant mechanism of tribofilms formed in alternated atmospheres is partially affected by their initial composition established at the beginning of sliding.The composite Mo-S-N solid lubricant films are synthesized by magnetron sputtering of molybdenum disulphide(MoS2)target in nitrogen and argon atmosphere.The results show that with the increase of the nitrogen content,the nitrogen concentration in the deposited films increases from 0 to 9.07 at.%,and the corresponding S/Mo atomic ratio reduces below to 1.20.Introducing nitrogen into films leads to the formation of amorphous structure and chemical bonds between nitrogen and molybdenum.The hardness and elastic modulus of Mo–S–N films increase more than one order of magnitude higher than that of pure MoS2 films with increasing the N2 flow rate,reaching to the maximum of 12.25 and 135.12 GPa,respectively.The tribological properties of the prepared films tested by a ball-on-disc tribometer under a low-pressure vacuum exhibit that the incorporation of a suitable content of N dopant could significantly reduce the wear rate,however,both friction coefficient and wear rate increase dramatically in excess a certain amount of N dopant.The C/N co-doping MoS2 composite films(Mo-S-C-N)with different sputtering power applied on graphite target were deposited by radio frequency magnetron sputtering of graphite and MoS2 targets in argon and nitrogen atmosphere.The influence of C/N co-doping on microstructure,mechanical and tribological properties of deposited films was analyzed using the various analytical techniques.The results show that increasing the sputtering power applied on graphite target leads to the increase of carbon concentration in the Mo-S-C-N composite films,resulting in the formation of dense structure and smooth surface.When the graphite target sputtering power reaches to 350 W,a self-assembled multilayer structure with periodicity in the nanometer scale formed.Benefiting from the compact and self-assembled multilayer structure,the maximum hardness of Mo-S-C-N film reaches up to 9.76 GPa,and corresponding friction experiment indicates that comparing to pure MoS2 film the composite films shows lower friction coefficient and high wear resistance both in high vacuum and ambient air conditions.