Preparation And Tribological Properties Study Of MoS₂/WS₂ Based Films With Controllable Structure

The lubrication system of the aerospac will inevitably contact with extremely harsh and complex environment such as high humidity and heat,high and low temperature alternation,and marine water vapor in the whole service life including test,storage,flight and launch.Although the traditional MoS₂/WS₂ based films have excellent vacuum lubrication performance,they can not meet the lubrication requirements of storage and flight in high temperature,high humidity and corrosion environment.In order to maintain the long-term stability of aerospace system,it is necessary to explore new MoS₂/WS₂ based films.In this thesis,MoS₂-W composite films with（002）crystal plane preferred orientation were successfully prepared by unbalanced closed field magnetron sputtering and the influence of W content on structure and high temperature tribology was investigated.Then,another kind of transition metal disulfide（WS₂）was introduced to prepare MoS₂/WS₂ composite and multilayer films.The effects of structure on tribological properties and multilayer interface on the diffusion barrier of corrosion particles were explored.In addition,MoS₂/WS₂-Ta films were also prepared and the influence of Ta on the structure,corrosion resistance and high temperature tribology of MoS₂/WS₂ multilayer films were investigated.The main conclusions were as follows:（1）W doping can inhibit the（100）and（110）orientations,but promote the（002）preferred orientation.Moreover,the hardness,elastic modulus and tribological properties were significantly improved and the sensitivity of MoS₂ tribological properties to temperature reduced.At 25℃,the reason for the poor tribology properties of MoS₂films was the physical adsorption of H₂O.At 300℃,the poor tribology properties resulted from serious oxidation.However,at 100℃,all the films exhibited the best tribological properties due to the significant reduction of H₂O adsorption.Optimized MoS₂-W composite films embraced better properties of tribology than pure MoS₂ when temperature varied from 25℃to 300℃.Especially,MoS₂-8.2 at%W film had the least wear rate and almost lowest coefficient of friction due to compacted microstructure,high hardness and good oxidation resistance,which became self-adaptive to temperature variations.（2）For MoS₂/WS₂ multilayer film,the alternate growth of MoS₂ and WS₂ single layer can interrupt the continuous growth of the same component film and promote the regular stacking growth of（002）plane parallel to the substrate.This kind of growth mode was beneficial to the formation of compact structure and the reduction of oxidation active sites,which made the tribological properties of MoS₂/WS₂multilayer film much better than MoS₂/WS₂ composite film.In addition,the interfaces in MoS₂/WS₂ multilayer film can not only enhance the mechanical properties by interface reinforcement effect,but also effectively prevent the diffusion of H₂O,O₂,Cl^-and Na⁺corrosion particles.Consequently,the oxidation resistance and corrosion resistance of MoS₂/WS₂ multilayer film were better than MoS₂/WS₂composite films.（3）Ta doping can optimize the structure of MoS₂/WS₂ multilayer film from incomplete to complete multilayer alternate structure and improve compactness,mechanical properties and corrosion resistance of MoS₂/WS₂ multilayer film.In addition,proper amount of Ta can improve the temperature adaptability of MoS₂/WS₂multilayer film and obtain the best comprehensive lubrication properties such as MoS₂/WS₂-1.8 at.%Ta.However,excessive Ta will cause more hard oxides phase to badly inhibit the formation of the transfer film and make wear sharply increase during the friction process,which will deteriorate the tribological properties.