MS₂（M=Mo，W） Composite Coatings Design And Investigation Of The Tribological Behavior

In this thesis,Mo S₂and WS₂coatings were prepared by a closed-field unbalanced magnetron sputtering system.The fretting and sliding friction properties of the coatings were investigated under different humidity conditions,finding that the coatings had high humidity sensitivity under sliding conditions.In order to improve the moisture resistance of Mo S₂and WS₂coatings,Mo S₂/Si and WS₂-W-DLC composite coatings were successfully prepared.The tribological properties of the composite coatings in the atmospheric environment were tested through friction and wear tests.The effects of doping elements on the microstructures,mechanical properties and tribological behaviors of the composite coatings were investigated in detail by using advanced characterization test methods such as FESEM,AFM,HRTEM,XRD and Raman spectroscopy.The main research results are as follows:（1）Under fretting conditions,the friction coefficient and wear rate of Mo S₂and WS₂coatings change to a small degree with the increasing of humidity;under sliding conditions,the friction coefficient is significantly increased as the humidity increases.The experiment results have shown that Mo S₂coatings are oxidized to formα-Mo O₃andβ-Fe Mo O₄during the friction process,while the oxidation products of WS₂coatings are mainly WO₂and WO₃.These hard particles cause abrasive wear of the coatings.In sliding conditions,due to the large displacement amplitude and grinding,the surface of wear track produces a larger area of?fresh surface.These fresh surfaces will be oxidized and produce more hard particles when exposed to a humid environment,and the as-produced hard particles can further intensify the abrasive wear and cause a significant decrease in the tribological performance;in the fretting conditions,due to the lower displacement amplitude,the coatings produce fewer hard particles during friction,leading to the slight wear.（2）The humidity sensitivity of Mo S₂coatings during sliding friction is decreased by doping Si element,and the effect of doping Si element on the structure and tribological properties of the coatings are systematically studied.The studies show that the doping of Si element change Mo S₂coatings from a columnar porous structure to an amorphous structure.When the Si content further increases to 17.3at.%,a multilayer nanostructure appears in the composite coatings.The introduction of Si improves the hardness of the coatings,and the doped Si element has an oxygen absorption effect during the friction process,which effectively improves the oxidation resistance of Mo S₂coatings in the atmospheric environment.Therefore,when the Si content increases from 0 to 14.7 at.%,the tribological properties of Mo S₂/Si coatings increase.However,excessive Si will also hinder the formation of the transfer film and lead to abrasive wear.Thus,Mo S₂/Si coatings with Si content of 17.3 at.%can hardly form a transfer film on the surface of the dual ball during the friction process,resulting in relatively bad tribological properties.（3）WS₂-W-DLC coatings were prepared by co-deposition of W-DLC and WS₂to decrease the humidity sensitivity of WS₂coatings during sliding friction,and the influence of doping elements on the structure and tribological properties of the coatings were investigated in detail.The experiment results have found that the doped C element does not react with WS₂,and the doping of W and C can significantly increase the hardness of the WS₂coatings.Therefore,the appropriate amount of W and C elements can effectively improve the anti-friction and anti-wear properties of the composite coatings in the atmospheric environment.However,with the increase of the C content,the ratio of sp³/sp²in the composite coatings also increases.Increasing the internal stress level of the coatings can reduce the film-base bonding force,resulting in a decrease in the wear resistance of the coatings.In addition,the composite coatings with C content greater than 9.94 at.%will form a double-layer graphite structure during the friction process.Because the number of graphite layers is few,the overall stiffness is small.It is easy to produce bulgy wrinkles under the action of shearing force,thereby hindering slide behavior.