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Friction and Wear Properties of Selected Solid Lubricating Films: Case Studies
Published in Kazuhisa Miyoshi, Solid Lubrication Fundamentals and Applications, 2019
Molybdenum disulfide is unsuitable as a dry lubricant in air because its reacts with oxygen and/or water vapor to form corrosive products [6.40, 6.41]. The ambient atmosphere in near Earth orbit consists of atomic oxygen and outgassing products from the spacecraft at pressures in the range 10−7 to 10−4 Pa [6.42, 6.43]. However, there is no evidence that these conditions are unsuitable for the use of MoSx films. On the contrary, Dimigen et al. [6.44] observed that the coefficient of friction of magnetron-sputtered MoSx films was substantially less when run in 10−6 to 10−4 Pa of oxygen than when run in ultrahigh vacuum (see dashed line in Fig. 6.18). Dimigen et al. measured the coefficient of friction for a range of rotational speeds and oxygen gas pressures on an MoS1.4 film by using a pin-on-disk tribometer. The dashed line in Fig. 6.18 is an attempt to represent the results of their tests at 50 rpm. They attributed these results to an adsorption-desorption phenomenon at the sliding interface rather than to a change in the chemistry or morphology of the material itself. However, the evidence for this conclusion was not clear, and the investigation of the oxygen effect was only a peripheral part of that work.
Optical Instrument Structural Design
Published in Paul Yoder, Daniel Vukobratovich, Opto-Mechanical Systems Design, 2017
Both gold and silver metallic platings are used to reduce friction coefficients. Silver in particular is common and is often used in both bearing and fastener applications. Some dry film lubricants, such as molybdenum disulfide, have a laminar structure with very low shear strength, again reducing the friction coefficient. A disadvantage of molybdenum disulfide is that the surface film may generate particulate contamination under sliding motion; this is overcome by special burnishing techniques prior to use.
Properties and Applications of Molybdenum
Published in C. K. Gupta, Extractive Metallurgy of Molybdenum, 2017
In a small number of applications of considerable technical significance, molybdenum is used directly in the purified form of its sulphidic mineral, molybdenum disulfide. The antiwear properties of molybdenum disulfide are well known. It is used as a dry lubricant. More extensive is its utilization as a lubricant additive in oils, greases, pastes, solid films, and other types of lubricants. The most widely recognized application is in the automobile industry, though. Moly sulfide lubricants have found use in almost every segment of industry. A low coefficient of friction (about 0.05) over a wide range of temperature (from cryogenic temperatures to 400°C or so in air and still higher temperatures in nonoxidizing atmospheres), retention of lubricating characteristics in vacuum, and efficiency under high load bearing application are some of the important properties of molybdenum disulfide which have accounted for its extensive use as lubricants either alone or in partnership with others (as additives to lubricants).
Friction-Induced Hardening Behaviors and Tribological Properties of 60NiTi Alloy Lubricated by Lithium Grease Containing Nano-BN and MoS2
Published in Tribology Transactions, 2019
Chao Yan, Qunfeng Zeng, Youchang Hao, Yating Xu, Ming Zhou
MoS2 nanoparticles also have a lamellar structure similar to that of h-BN (Demas, et al. (23)). Within the layers, each Mo atom is coordinated by six S atoms in a trigonal prismatic arrangement by strong S-Mo-S bonds. The nearest layers are connected by van der Waals bonds, which results in easy slippage or breakage by simply “pulling off” the MoS2 layers (Benavente, et al. (16)). However, molybdenum disulfide is fragile during the friction process, and the fragmented particles are easily deteriorated by chemical reaction with the surrounding atmosphere, which will reduce its friction reduction performance (Guo (24)).
Deep learning-based supervised and unsupervised neural networks for analysing the characteristics of powder composite preforms
Published in International Journal of Modelling and Simulation, 2021
Radha Pavanasam, Chandrasekaran G., N. Selvakumar
Atomised aluminium powder of – 150 μm size was used with initial aspect ratio values in the range 0.50, 0.75 and 1.00. The load (L) was applied from 5 to 120. The given load is directly proportional to deformation and strain-hardening properties. Molybdenum disulphide (MoS2) is used as lubricant to prepare the composite. The partial database of input features used in this work is shown in Table 1, and partial database of output data is given in Table 2.
Performance Evaluation of a Hard Composite Solid Lubricant Coating When Dry Machining of High-carbon Steel
Published in Tribology Transactions, 2018
S. Gangopadhyay, D. Bhaduri, A. K. Chattopadhyay, S. Paul
Molybdenum disulfide (MoS2) is a widely accepted solid lubricant coating that has been extensively used for components subject to friction and wear (Wang, et al. (10); Luo, et al. (11)). The superlubricity behavior of MoS2 fostered its implementation in machining and the coating has been mainly employed in drilling and milling operations (Renevier, et al. (12)). Rechberger and Dubach (13) showed that MoS2-coated high speed steel (HSS) end mills provided better workpiece surface finish and a twofold higher productivity compared to the uncoated cemented carbide counterparts. However, due to its low hardness and poor resistance to oxidation under a humid environment, MoS2 has been applied in machining either as a top coat with a hard underlayer (Settineri and Levi (14)) or as a multilayer (Kustas, et al. (5)) or a non-multi-layer composite coating (Teer, et al. (15)). Further, MoSx-based coatings could not be successfully implemented in turning steel materials due to the high machining temperatures encountered. Liu, et al. (16) stated that MoS2 coatings were not useful for all machining conditions; its effectiveness depended on the appropriate matching of cutting tools and workpieces that were related to the cutting temperature. MoSx-Ti composite coating with hard underlayers such as TiC, TiCN, and TiN did not exhibit any improvement in tool life compared to that obtained with the monolayer hard coatings when turning 34CrNiMo6 steel (Renevier, et al. (17)). Deng, et al. (18) and Song, et al. (19) reported that MoSx-Zr composite-coated carbide turning tools led to a reduction in cutting force and improved tool life compared to those obtained with the uncoated inserts when the cutting velocity was lower than 120 m/min. However, the same coating did not exhibit any improvement in performance at cutting velocities greater than 120 m/min. More recently, Ilyuschenko, et al. (20) demonstrated that drills coated with alternating layers of chromium, nanodiamond, and MoS2-Cr were capable of restricting burr and built-up edge (BUE) formation and consequently augmenting the tool life when machining AlSi9Cu3(Fe) aluminum alloy, in comparison to the uncoated counterparts. A minority of papers also detailed use of tungsten disulfide (WS2) as a soft lubricating coating when dry turning of quenched and tempered AISI 1045 steel, with results indicating a reduction in cutting force and temperature at a high cutting speed of 200 m/min with respect to the uncoated carbide insert (Lian, et al. (21)).