Tribological Behavior Of MoS₂/C Composite Films

MoS₂ solid lubricating films are widely used in the field of space and vacuum because its layered structure is easy to shear.However,the pure MoS₂ is easily oxidized by water vapor and oxygen,and the MoS₂ thin film prepared by the traditional sputtering method has a loose and porous structure,which makes the erosion more serious,thus limiting the application environment of MoS₂ solid lubricating film.In order to improve antioxidant and moisture resistance of MoS₂,doping MoS₂ with other elements is mostly chosen.A relatively successful method is the combination of MoS₂ and C,which can greatly enhance the film’s compactness,and ultimately get both mechanical properties and lubrication performance.In this paper,MoS₂ / C composite films with a Ti interlayer were prepared by DC magnetron sputtering technique and high power pulsed magnetron sputtering technique（HiPIMS）.The friction and wear behavior of the composite films under different environment and different test conditions were analyzed emphatically.The composite films with different compositions were prepared by sputtering MoS₂ and carbon composite targets.The composite films were densely amorphous.Amorphous MoS₂ was dispersed in amorphous carbon matrix.The compact structure makes the film have excellent mechanical properties.The composite film has a hardness of up to 8.7GPa with the C content of 84.3 at.%.Tribologic results showed that the films with higher carbon content in the atmosphere have better tribological properties.Based on the analysis of the worn surface and wear products,it is concluded that the synergistic effect of re-ordering of amorphous carbon,and transformation of amorphous MoS₂ into ordered MoS₂ and the releasing of amorphous carbon from transfer film was account for the low friction and wear behavior.In vacuum,the composite film with higher MoS₂ content had a lower friction coefficient because of the adhesion between the dangling bond of amorphous carbon;Stribeck curve deduced from the tribological behavior in the oil environment,showed that the composite film has lower friction and wear properties during the boundary lubrication stage,due to the excellent lubricating property of the solid lubricating film;In high temperature environment,friction coefficient of the composite film decreased with the increase of temperature.A higher temperature would promote the graphitization of amorphous carbon and the crystallization of MoS₂.But excessive high temperature would induce the oxidation of MoS₂ and accelerate the film failure.The results of different test conditions showed that the decrease of the friction coefficient of the composite film was mainly attributed to the contribution of the Hertz contact;During the tests of using different tribopairs,it found that the composite film showed low friction coefficient for ZrO2 and Al2O3,which can avoid the adhesion of amorphous carbon under the vacuum condition.Specially,the use of ZrO2 tribopair can reduce the critical content of MoS₂ of the composite film to achieve low friction in vacuum.