Extreme tribology

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Extreme tribology refers to tribological situations under extreme operating conditions which can be related to high loads and/or temperatures, or severe environments. Also, they may be related to high transitory contact conditions, or to situations with near-impossible monitoring and maintenance opportunities. In general, extreme conditions can typically be categorized as involving abnormally high or excessive exposure to e.g. cold, heat, pressure, vacuum, voltage, corrosive chemicals, vibration, or dust. [1] The extreme conditions should include any device or system requiring a lubricant operating under any of the following conditions: [2]

Contents

Operation in such extreme conditions is a great challenge for tribologists to develop tribosystems that could meet these extreme requirements. Often, only multifunctional materials fulfill such requirements. [3]

Challenges in tribology

The progression of the humanity suggested new technologies, devices, materials and surface treatments which required novel lubricants and lubrication systems. Likewise, the development of high-speed trains, aircraft, space stations, computer hard discs, artificial implants, and bio-medical and many other engineering systems, have only been possible through the advances in tribology. Challenges in tribology including sustainability, climate change and gradual degradation of the environment require new solutions and innovative approaches. [4]

Tribology at extreme temperatures

In many tribological applications, the system components are exposed to extreme temperatures (very high or ultra-low temperatures). Examples of such applications can be found in the aerospace, mining, power generation, metalworking industries, and steel plants. In tribology, an application can be considered to operate at elevated temperatures when the use of conventional lubricants, i.e. oils and greases is no longer effective due to their rapid decomposition at around 300 °C. Smart lubricating materials and multifunctional lubricating materials are developed as new class materials with increased safety, long-term durability and as less amount of repairing costs as possible. Such materials are designed to be self-diagnostic, self-repairing, and self-adjusting. These materials include structural/lubricating integrated material, anti-radiation lubricating material, conductive or insulation lubricating material, etc. At low temperatures and in cryogenic environments, liquid lubricants can solidify or become highly viscous and not be effective. On the other end, solid lubricants have usually been found to be better than liquid lubricants or greases. The most common solid lubricants for cryogenic temperature are polytetrafluoroethylene, polycarbonate, tungsten disulphide (WS2), and molybdenum disulphide (MoS2). In addition, ice could be a possible lubricant for deformation in cryogenic environments which provides a method of self-lubrication in the sense that no active mechanism is needed to supply a lubricant.

Tribology at micro/nano-scale

The fundamental difference that distinguishes micro/nano tribology from classical macro tribology is that micro/nano tribology considers the friction and wear of two objects in relative sliding whose dimensions range from micro-scales down to molecular and atomic scales. MEMS refer to micro-electromechanical systems that have a characteristic length of 100 nm to 1 mm, while NEMS are the nano-electromechanical systems that have a characteristic length of less than 100 nm. [5] There are great challenges in the development of a fundamental understanding of tribology, surface contamination and environment in MEMS/NEMS. One of these challenges in such extreme tribological situations is the adhesion force which can be up to a million times greater than the force of gravity. This is due to the fact that the adhesion force decreases linearly with size, whereas the gravitational force decreases with the size cubed. Low surface energy, hydrophobic coatings applied to oxide surfaces are promising for minimizing adhesion and static-charge accumulation. [6]

Tribology under vacuum conditions

Under vacuum environment, it is a problem to achieve acceptable endurance of tribological components due to the fact that the lubricant may either freeze, evaporate or decompose and hence become ineffective. Tribological properties of materials exhibit different characteristics at the space vacuum as compared to the atmospheric pressure. Adhesive and fatigue wear are the two important types of wear encountered in a vacuum environment. Vacuum not only radically affects the wear behavior of metals and alloys in contact, but also has a pronounced influence on nonmetals as well. [7] [8] Different new kinds of materials are developed for potentially operating in vacuum environments. For instance, CuZn
39Pb
3 and Ni
3(Si,Ti) alloys have excellent anti-wear properties in all the vacuum conditions. [9] [10] [11] Types of solid lubricants used in space applications:

The most common way to utilize a solid lubricant is to apply it to a metal surface as a film or surface coating of a thin layer of soft film, typically molybdenum disulphide, artificially deposited on the surfaces. Coatings of solid lubricant are built up atom by atom yielding a mechanically strong surface layer with a long service life and the minimum quantity of solid lubricant.

Geotribology

The term "geotribology" was first stated by Harmen Blok with no significant discussion. [12] Later, geotribology framework was employed to analyze the flow mechanics of granular sand. [13] Even though tribological concepts can be utilized to many geosciences phenomena, the two research communities are separated. In earth science, many tribological concepts were applied successively, particularly in rock friction analyses. The asperity-asperity contact mechanism was applied to rock friction experiments that led to the rate-state friction law that prevails in earthquake analyses. [14]

Tribology in high dust and dirty areas

High dust areas and dirt environments can weigh profoundly on a lubricant due to the high risk of particle contamination. These contaminants readily form a grinding paste, causing failure of tribosystems and subsequently damaging of equipment. This type of contamination most frequently takes place when airborne or stagnant particles gain access to the lubrication system through open ports and hatches, especially in systems with negative pressure. Half of a bearing loss of usefulness can be attributed to wear. This wear, which occurs through surface abrasion, fatigue and adhesion, is often the result of particle contamination.

Tribology in radiation environments

In radiation environments, liquid lubricants can decompose. Suitable solid lubricants can extend the operation of systems beyond 106 rads while maintaining relatively low coefficients of friction.

Tribology for limited weight applications

In weight-limited spacecraft and rovers, solid lubrication has the advantage of weighing substantially less than liquid lubrication. The elimination (or limited use) of liquid lubricants and their replacement by solid lubricants would reduce spacecraft weight and, therefore, have a dramatic impact on mission extent and craft maneuverability.

Related Research Articles

<span class="mw-page-title-main">Friction</span> Force resisting sliding motion

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal.

A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

<span class="mw-page-title-main">Molybdenum disulfide</span> Chemical compound

Molybdenum disulfide is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is MoS
2.

<span class="mw-page-title-main">Lubrication</span> The presence of a material to reduce friction between two surfaces.

Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology.

<span class="mw-page-title-main">Wear</span> Damaging, gradual removal or deformation of material at solid surfaces

Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical or chemical. The study of wear and related processes is referred to as tribology.

Tribology is the science and engineering of understanding friction, lubrication and wear phenomena for interacting surfaces in relative motion. It is highly interdisciplinary, drawing on many academic fields, including physics, chemistry, materials science, mathematics, biology and engineering. The fundamental objects of study in tribology are tribosystems, which are physical systems of contacting surfaces. Subfields of tribology include biotribology, nanotribology and space tribology. It is also related to other areas such as the coupling of corrosion and tribology in tribocorrosion and the contact mechanics of how surfaces in contact deform. Approximately 20% of the total energy expenditure of the world is due to the impact of friction and wear in the transportation, manufacturing, power generation, and residential sectors.

<span class="mw-page-title-main">Plain bearing</span> Simplest type of bearing, with no rolling elements

A plain bearing, or more commonly sliding contact bearing and slide bearing, is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore, the journal slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests on or the ways on the bed of a lathe.

<span class="mw-page-title-main">Galling</span> Form of wear caused by adhesion between sliding surfaces

Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, whereas the galled material may appear gouged with balled-up or torn lumps of material stuck to its surface.

Nanotribology is the branch of tribology that studies friction, wear, adhesion and lubrication phenomena at the nanoscale, where atomic interactions and quantum effects are not negligible. The aim of this discipline is characterizing and modifying surfaces for both scientific and technological purposes.

Fretting refers to wear and sometimes corrosion damage of loaded surfaces in contact while they encounter small oscillatory movements tangential to the surface. Fretting is caused by adhesion of contact surface asperities, which are subsequently broken again by the small movement. This breaking causes wear debris to be formed.

Solid film lubricants are paint-like coatings of very fine particles of lubricating pigment blended with a binder and other additives. The lubricant is applied to a substrate by spray, dip or brush methods and, once cured, creates a solid film which repels water, reduces friction and increases the wear life of the substrate to which it has been applied. Certain film lubricants also offer additional properties such as corrosion inhibition. Solid film lubricants are used in the automotive, transportation and aerospace industries. 2 commonly used ones are graphite and molybdenum disulfide.

ApNano Materials is a nanotechnology company, wholly owned and operated by Nanotech Industrial Solutions (NIS) with R&D lab, manufacturing, blending and packaging facilities in Avenel, New Jersey, United States, and Yavne, Israel. NIS is the only company in the world with an exclusive license to manufacture inorganic fullerene-like tungsten disulfide (IF-WS2) submicron (nanosized) spherical particles on a commercial scale with the patent from the Weizmann Institute. These inorganic fullerene-like tungsten disulfide-based nanomaterials opened up new possibilities for developing extreme performance industrial lubricants, coatings, and polymer composites.

Compacted oxide layer glaze describes the often shiny, wear-protective layer of oxide formed when two metals are slid against each other at high temperature in an oxygen-containing atmosphere. The layer forms on either or both of the surfaces in contact and can protect against wear.

Friction modifiers are added to lubricants in order to reduce friction and wear in machine components. They are particularly important in the boundary lubrication regime, where they can prevent solid surfaces from coming into direct contact, substantially reducing friction and wear.

<span class="mw-page-title-main">Polyphenyl ether</span> Class of polymers

Phenyl ether polymers are a class of polymers that contain a phenoxy or a thiophenoxy group as the repeating group in ether linkages. Commercial phenyl ether polymers belong to two chemical classes: polyphenyl ethers (PPEs) and polyphenylene oxides (PPOs). The phenoxy groups in the former class of polymers do not contain any substituents whereas those in the latter class contain 2 to 4 alkyl groups on the phenyl ring. The structure of an oxygen-containing PPE is provided in Figure 1 and that of a 2, 6-xylenol derived PPO is shown in Figure 2. Either class can have the oxygen atoms attached at various positions around the rings.

Oil additives are chemical compounds that improve the lubricant performance of base oil. The manufacturer of many oils can use the same base stock for each formulation and can choose different additives for each use. Additives comprise up to 5% by weight of some oils.

Dry lubricants or solid lubricants are materials that, despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid oil medium.

Chameleon coating, also known as nano composite tribological coating, is an adaptive adhesive that uses nanotechnology to adjust to environmental fluctuations to make living conditions more suitable to the object that the coat has been applied to.

Space tribology is a discipline in the field of tribology which deals with tribological systems for spacecraft applications. Research in the field aims to design reliable tribological systems that can withstand the harsh environment of space.

Tribofilms are films that form on tribologically stressed surfaces. Tribofilms are mostly solid surface films that result from a chemical reaction of lubricant components or tribological surfaces.

References

  1. ↑ "Engineering Systems for Extreme Environments". studylib.net. Retrieved 2023-10-13.
  2. ↑ Pinchuk, D., et al. Tribology and Lubrication in Extreme Environments (Two Case Studies). 2002.
  3. ↑ "Multifunctionality of Polymer Composites". 2015. doi:10.1016/c2013-0-13006-1.{{cite journal}}: Cite journal requires |journal= (help)
  4. ↑ Stachowiak, Gwidon W. (2017-09-01). "How tribology has been helping us to advance and to survive". Friction. 5 (3): 233–247. doi: 10.1007/s40544-017-0173-7 . hdl: 20.500.11937/59306 . ISSN   2223-7704.
  5. ↑ Mylvaganam, K.; Zhang, L. C. (2011-01-01), Davim, J. Paulo (ed.), "4 - Micro/nano tribology", Tribology for Engineers, Woodhead Publishing, pp. 121–160, doi:10.1533/9780857091444.121, ISBN   978-0-85709-114-7 , retrieved 2023-10-13
  6. ↑ de Boer, M.P.M., T.M. Tribology of MEMS. 2001. DOI: 10.1557/mrs2001.65
  7. ↑ Buckley, Donald H. (1974-01-01). "Adhesion, Friction, Wear and Lubrication in Vacuum". Japanese Journal of Applied Physics. 13 (S1): 297. doi:10.7567/JJAPS.2S1.297. ISSN   1347-4065.
  8. ↑ Radchik, V. and A. Radchik, About the Deformations on the Surface Layer in Sliding Friction. Rep. Acad. of Sciences, USSR, 1958. 119(5): p. 933-935.
  9. ↑ Küçükömeroğlu, Tevfik; Kara, Levent (2014-01-15). "The friction and wear properties of CuZn39Pb3 alloys under atmospheric and vacuum conditions". Wear. 309 (1): 21–28. doi:10.1016/j.wear.2013.10.003. ISSN   0043-1648.
  10. ↑ Liu, C. T.; George, E. P.; Oliver, W. C. (1996-01-01). "Grain-boundary fracture and boron effect in Ni3Si alloys". Intermetallics. 4 (1): 77–83. doi:10.1016/0966-9795(95)96901-5. ISSN   0966-9795.
  11. ↑ Niu, Muye; Zhang, Xinghua; Chen, Jiajun; Yang, Xiaoyuan (2019-03-01). "Friction and wear properties of Ni3Si alloy under different vacuum conditions". Vacuum. 161: 443–449. doi:10.1016/j.vacuum.2019.01.015. ISSN   0042-207X.
  12. ↑ Blok, H. (1963-11-01). "The flash temperature concept". Wear. 6 (6): 483–494. doi:10.1016/0043-1648(63)90283-7. ISSN   0043-1648.
  13. ↑ Dove, J.E. and J.B. Jarrett, Behavior of dilative sand interfaces in a geotribology framework. Journal of Geotechnical and Geoenvironmental Engineering. 128(1): p. 25-37.http://www.worldcat.org/oclc/926205493
  14. ↑ 20. Bowden, F.P. and D. Tabor, The Friction and Lubrication of Solids. 1950, U.K.: Clarendon Press Oxford.
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