二硫化钼溅射膜在潮湿空气中贮存后润滑性能的退化与失效机理

Study on the Mechanism of Lubrication Degradation and Failure of MoS2 Sputtered Films Stored in the Moist Air

为了探讨ＭｏＳ＿２溅射膜在潮湿空气中贮存期间所发生的化学变化这个长期争议未了的问题，以空间机械常用的９Ｃｒ１８轴承钢为底材，利用ｒｆ溅射法沉积ＭｏＳ＿２薄膜，并且利用Ｘ射线光电子能谱仪、俄歇电子能谱仪和Ｘ射线衍射仪等对这种薄膜在室温（１１－１５℃）下于相对湿度为１００％的潮湿空气中贮存不同时间后的组成、元素价态和晶体结构进行了分析，考察了它在潮湿贮存过程中所发生的化学变化及其润滑性能的退化与失效机理，检测发现，ＭｏＳ＿２溅射膜经潮湿贮存一天就有少量的Ｍｏ￣（４＋）氧化生成了Ｍｏ￣（６＋），在潮湿贮存５天时又发现有少量的ＳＯ生成，随着贮存时间的延长，不仅膜中Ｍｏ￣（６＋）／Ｍｏ￣（４＋）之比在不断地增大，表明有更多的Ｍｏ￣（４＋）发生了深度氧化，而且Ｓ￣（２－）发生氧化生成的ＳＯ之含量也越来越大。由此可见，ＭｏＳ＿２溅射膜在室温下于潮湿空气中贮存期间与氧和水发生了化学反应，生成物是ＭｏＯ＿３和Ｈ＿２ＳＯ＿４．Ｈ＿２ＳＯ＿４的生成致使薄膜表面的凝聚水呈现出ｐＨ值为１．５－２．０的强酸性，从而造成了金属底材的腐蚀。ＭｏＳ＿２的深度氧化和金属底材的腐蚀是导致ＭｏＳ＿２溅射膜在潮湿环境中润滑性能退化与失效的主要原因。

The mechanism of lubrication degradation and failure of MoS2 stored in the moist airfor a given period is a difficult problem which has been disputed internationally for 30 years.Because of the lack of enough experimental data,no unanimous conclusion has been drawn.The MoS2 film was deposited on the substrate 9Cr18 bearing steel which used for spacemechanism by rf sputtering deposited method in this paper. Under room temperature(11-15℃)and stored for different period in the moist air with relative humidity of 100%,the composition,element valence and crvstal structure of MoS2 film was analyzed using X-ray photoelectronspectrometry(XPS).Auger electron spectroscopy(AES) and X-ray diffraction(XRD ),and thenrevealed the various changes degradation of lubrication and failure mechanism during storing processin the moist air. The results shown that a small amount of Mo4+ was oxidized into Mo6+ whenMoS2 sputtered film is stored in the moist air for one day, whereas stored for five days,a fewamount of SO was produced.With still longer storing time,not noly the ratio of Mo6+ to Mo4+ infilm increased continuously, from the deeper oxidation of Mo4+ but also the SO content which isresulted from S2- oxidation increased gradually.Thus,it is suggested that the main chemicalreaction of MoS2 sputtered film in the moist air is as follow:The production of H2SO4 leads to the pH value decreasing to 1.5-2.0 and presenting strongacidity,so the substrate is eroded. The conclusion is that the deep oxidation of MoS2 and erosion of substrate is the main reason oflubrication degradation and failure of MoS2 sputtered film stored in the moist air.