Preparation Of W-Ti/MoS₂ Composite Coating And Its Anti-corrosion And Wear-resistant Propertie

MoS₂ layered solid lubricant has excellent lubricating properties in space environment,but it is easily affected by water vapor and oxygen in ordinary atmospheric environment,resulting in the decline of lubricity and wear resistance.By adding metal dopants with excellent oxidation resistance can improve the performance limitations of MoS₂ in aerospace and other applications.However,in practical application,the wear resistance of MoS₂coating prepared by spraying method still need to be improved due to its loose structure and poor adhesive strength.What’s more,the aerospace components used in naval aircraft has to face a more demanding and complex service environment.Based on the problems MoS₂coating facing in industrial application,the W-Ti/MoS₂composite coating with different W-Ti content of 1.82,6.0,8.0,10.4 and 11.0 at.%was prepared by magnetron sputtering process via controlling the co-sputtering power.Meanwhile,the pure MoS₂ thin layer was designed on the top to further improve its lubrication performance.By means of EDS,XRD,SEM,3D morphology test,nano indentation and scratch,the relationship between the content of W-Ti and the crystal growth,microstructure and mechanical properties of the coatings was discussed.The influence of metal doping on hydrophilicity and hydrophobicity and corrosion resistance of the coatings was studied by means of contact angle test,electrochemical corrosion test and salt spray corrosion test.The tribological properties of the coatings were studied in ordinary atmospheric environment and simulated marine atmospheric environment（salt spray environment）,and the wear products in salt spray environment were analyzed by XPS.The microscopic characterization and mechanical properties testing results of the coatings show that the W-Ti doping changes the growth mode of MoS₂:the pure MoS₂coating are randomly oriented and dominated by（100）edge planes,while W-Ti/MoS₂composite coatings exhibit a highly ordered preferred orientation along the（002）basal plane,and MoS₂ gradually becomes amorphous from the polycrystalline state with increasing W-Ti doping content.Appropriate content of W-Ti doping（8.0 at.%）makes the composite coating have a denser microstructure,lower surface roughness and better film-matrix bonding strength,and the hardness and elastic modulus are also changed from 0.32GPa and56.2GPa of the pure MoS₂ to 6.94GPa and 92.28GPa of the WT80 composite coating.In addition,the hardness of the coating generally increases with increasing W-Ti doping content.According to the hydrophilic and hydrophobic properties of prepared coatings,the pure MoS₂ coating has a contact angle of 84.4°and the hydrophobic properties were improved obviously by W-Ti metal doping.In addition,the contact angle increased first and then decreased with the increase of doping content and the maximum contact angle was 130.7°for the optimal content of 8.0 at%.The results of electrochemical corrosion study showed that the addition of W-Ti metal dopant leads to a negative shift of the open circuit potential of the coatings.However,according to the quantitative results of Tafel and EIS,the dopant could significantly improve the corrosion resistance of MoS₂coating by improving its microstructure.The corrosion resistance of composite coating with 8.0 at.%W-Ti higher than that of pure MoS₂ coating by two orders of magnitude.The results of salt spray corrosion show that the corrosion resistance of the composite coating with the best doping content（8.0at.%）higher than that of the pure MoS₂ coating without salt spray by one order of magnitude though after 16 days of salt spray corrosion.The wear test results of the coatings show that W-Ti/MoS₂ composite coating with dense orientation along（002）base plane has better lubricity and wear resistance than pure MoS₂ coating.The friction coefficient and wear rate of pure MoS₂ coating are 0.125～0.15and（6.21±0.35）×10-5mm³/Nm,respectively.However,the friction coefficient of W-Ti/MoS₂ composite coating with different doping content is 0.05～0.10,and the wear rate is10^-6 magnitude.The composite coating with 11.0 at%doping has the lowest stable friction coefficient（～0.05）,and the composite coating with 8.0 at.%doping has the lowest wear rate（～1.11×10-6mm³/Nm）.Due to the influence of water vapor and/or oxygen,the friction coefficient and wear rate of the MoS₂ coatings in the salt spray environment increased to a certain extent compared with them in common environment.The XPS analysis results show that the oxides ware the main wear products of the coatings in the salt spray environment.Compared with pure MoS₂ coating,the W-Ti/MoS₂ composite coating can effectively slow down the oxidation of MoS₂ due to the exist of W-Ti.But,according to the XPS results,the anti-oxidation protection performance of Ti element on MoS₂ is better than that of W element.