真空宽载下二硫化钼/碳复合薄膜的超低磨损机制

Ultra-low Wear Mechanism of Molybdenum Disulfide/carbon Composite Films under Vacuum Wide Load

空间装备正朝着重载、长时间运行的方向发展,对润滑材料的性能要求日益提高。当前二硫化钼(MoS_(2))薄膜主要在真空低载下(<0.5 GPa)服役,因此须发展针对真空宽载(中高载)下服役的二硫化钼复合薄膜。通过非平衡磁控溅射技术制备MoS_(2)/DLC复合薄膜,利用SEM、AFM、XRD、XPS、Raman、TEM、真空摩擦试验机等分析薄膜结构、形貌、摩擦学性能及磨损机制。结果显示:DLC的加入能够改善MoS_(2)柱状结构,使复合薄膜更加致密,并且能够促进薄膜以(002)晶面择优取向生长。复合薄膜在真空宽载(0.73~1.27GPa)下均能保持稳定的低摩擦因数(0.02~0.06)和低磨损率(10-10mm^(3)·N^(-1)·m^(-1)),与MoS_(2)相比降低了三个数量级。通过对磨屑进行分析,发现复合薄膜在摩擦过程能发生石墨化转变,形成有序的石墨结构以及润滑性能优良的(002)取向的MoS_(2),同时在MoS_(2)催化作用及接触应力诱导下,形成的层间低剪切力的石墨结构及层状的MoS_(2)有利于实现低摩擦因数和低磨损率。非晶碳的加入使得复合薄膜在真空环境下能够保持低摩擦因数和超低磨损率。通过复合结构设计实现了二硫化钼/碳复合薄膜在真空宽载条件下的超低磨损,可为空间超低磨损薄膜的设计、开发和应用提供一定的实验基础和理论指导。

The evolution of space equipment has been progressing to support heavier loads and longer durations of operation,necessitating the advancement of higher-performance lubricating materials.Currently,molybdenum disulfide(MoS_(2))films are predominantly used under low vacuum loads(<0.5 GPa),underscoring the urgent need for developing MoS_(2)composite films that can perform under a wider range of vacuum loads,including medium and high loads.In this study,MoS_(2)/diamond-like carbon(DLC)composite films were carefully fabricated using non-equilibrium magnetron sputtering technology.A variety of analytical methods,such as scanning electron microscopy(SEM),atomic force microscopy(AFM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy,transmission electron microscopy(TEM),and vacuum friction testing,were utilized to thoroughly assess the structure,morphology,tribological properties,and wear mechanisms of the films.The SEM images clearly show that the DLC film's surface is densely structured,consisting of closely packed small particles of similar sizes,without noticeable defects such as cracks or holes.Conversely,the surface of the MoS_(2)film features a worm-like structure,leading to a surface that is not smooth.When comparing the surface morphology of the MoS_(2)/DLC composite film to that of the DLC film,it is observed that both surfaces are composed of uniform small particles;however,the composite film’s particles create a rough,island-like structure.This is attributed to the amorphous growth of the DLC film,which disrupts the one-dimensional growth pattern of MoS_(2).Compared to the MoS_(2)film,the cross-sectional organization of the composite film shows an improvement,with a less pronounced columnar structure leading to a denser film structure.The presence of amorphous carbon prevents the formation of the columnar structure in MoS_(2),effectively mitigating the issues of pores,cracks,and other defects in the MoS_(2)film.Notably,the XRD diffraction peaks of the composite film were primarily observed at the(002)crystal face,with amorphous carbon aiding the film's growth and promoting a preferred orientation on this crystal face,which enhances its lubrication effectiveness.The hardness of the composite film increased significantly to 8.13 GPa,marking an eightfold improvement over the pure MoS_(2)film.Additionally,the surface roughness of the composite film was significantly reduced to 1.66 nm,in contrast to the higher surface roughness of 5.89 nm exhibited by the pure MoS_(2)film.The hardness of the MoS_(2)/DLC film also showed a significant increase when compared to the MoS_(2)film.The inherent low hardness of the MoS_(2)film,which leads to high wear rates,is effectively countered by the addition of carbon,increasing the composite film's hardness and thereby reducing its wear rate.The elastic recovery rate of the composite film was also found to be improved over the MoS_(2)film.The integration of DLC with MoS_(2)modifies the MoS_(2)film's structure,incorporating the DLC film's high hardness advantage into the composite,enhancing its performance under medium to high loads.XPS analysis confirmed that the composite film is predominantly composed of 2H-MoS_(2),favoring effective lubrication.To evaluate the tribological properties of the composite film,comprehensive testing was conducted under a wide range of vacuum loads,from 0.73 GPa to 1.27 GPa,showing the film's ability to consistently maintain a low friction coefficient(0.02–0.06)and a low wear rate 10-10 mm^(3)·N^(-1)·m^(-1).Comparative analysis has shown that,relative to MoS_(2)alone,the composite film significantly lowers both the friction coefficient and wear rate by three orders of magnitude.Further detailed examination revealed that the composite film is capable of undergoing a graphitization transformation,which leads to the creation of ordered graphite structures.These structures effectively lubricate MoS_(2)with a(002)orientation,a process induced by both the catalytic effect of MoS_(2)and contact stress.The development of layer-intercalated low shear stress graphite structures and layered MoS_(2),facilitated by the catalytic influence of MoS_(2)and contact stress,was identified as crucial for attaining both a low friction coefficient and wear rate.The incorporation of amorphous carbon into the composite film plays a significant role in enabling it to sustain a low friction coefficient and an ultra-low wear rate,even within a vacuum environment.Moreover,this study not only contributes practical insights but also offers valuable theoretical guidance for the future application,design,and development of MoS_(2)/carbon composite films.