Revisiting the dwell effect on friction behavior of molybdenum disulfide
Revisiting the dwell effect on friction behavior of molybdenum disulfide
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DOI：
10.1016/j.wear.2023.204876
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发表时间：
2023-04
期刊：
影响因子：
5
通讯作者：
T. Babuska;B. Krick;N. Argibay;M. Dugger;M. Chandross;J. Curry
中科院分区：
文献类型：
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作者：
T. Babuska;B. Krick;N. Argibay;M. Dugger;M. Chandross;J. Curry
固体润滑剂，如二硫化钼（MoS2）经常用于空间应用，并且在使用前（即在储存、运输或在工作周期之间）组件长时间处于静止状态。当休眠后恢复滑动时，二硫化钼的摩擦行为会因各种因素而变化，如累积的吸附物和氧化。这种现象被称为停留或停止时间效应，在50多年前首次被研究，其特征是摩擦系数的增加和长时间的磨合回到稳态摩擦。近五十年过去了，人们仍然没有很好地理解驻留效应的基本驱动机制。在这项工作中，通过在7 × 10−9到2 × 10−1torr压力下的间歇滑动实验，研究了mos2涂层的驻留效应，驻留时间从30秒到48小时（172,800秒）。改变真空压力以研究表面污染物（即水）的作用。结果表明，摩擦系数的变化是由水与滑动界面的相互作用驱动的。采用纳米晶溅射沉积和高取向喷涂的mos2涂层，研究了微观结构对驻留效果的影响。结果表明，由于减少了可能与污染物相互作用的潜在边缘位置，溅射沉积涂层的剪切改性表面的停留效应比喷涂沉积表面小2倍。此外，真空退火后的间歇滑动实验表明，可以通过从涂层中去除插层水来减少潜在水的贡献。
Solid lubricants, like molybdenum disulfide (MoS2) are often used in space applications, and subject to prolonged periods where components sit stationary before use (i.e., during storage, transport or in between duty cycles). When sliding is resumed after dormancy, the friction behavior of MoS2can vary due to a variety of factors such as accrued adsorbates and oxidation. This phenomenon, referred to as the dwell or stop-time effect, was first investigated over 50 years ago, and is characterized by an increase in the coefficient of friction and a prolonged run-in back to steady-state friction. After nearly five decades, the fundamental driving mechanism for the dwell effect is still not well understood. In this work, the dwell-effect for MoS2coatings is studied through intermittent sliding experiments with dwell times ranging from 30 s to 48 h (172,800 s) at pressures from 7 × 10−9to 2 × 10−1torr. Vacuum pressure was varied to investigate the role of surface contaminants (i.e., water). Results suggest that the change in the coefficient of friction is driven by interactions of water with the sliding interface. The role of microstructure on the dwell effect was investigated using nanocrystalline sputter-deposited and highly oriented spray-deposited MoS2coatings. Results show that the shear-modified surfaces of sputter-deposited coatings have a ∼2 × smaller dwell effect than spray-deposited surfaces due to the reduction of potential edge-sites that can interact with contaminants. Additionally, intermittent sliding experiments after vacuum annealing show that the contribution of latent water can be minimized by driving intercalated water from the coating.