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  1. 1. RECENT ADVANCES IN TRIBOLOGY Page 1 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 1. INTRODUCTION 1.1BACKGROUND Tribology in a traditional form has been in existence since the beginning of recorded history. There are many well documented examples of how early civilizations developed bearings and low friction surfaces. The scientific study of tribology also has a long history, and many of the basic laws of friction, such as the proportionality between normal force and limiting friction force, are thought to have been developed by Leonard0 da Vinci in the late 15th century. However, the understanding of friction and wear languished in the doldrums for several centuries with only fanciful concepts to explain the underlying mechanisms. For example it was proposed by Amonton in 1699 that surfaces were covered by small spheres and that the friction coefficient was a result of the angle of contact between spheres of contacting surfaces. A reasonable value of friction coefficient close to 0.3 was therefore found by assuming that motion was always to the top of the spheres. The relatively low priority of tribology at that time meant that nobody really bothered to question what would happen when motion between the spheres was in a downwards direction. Unlike thermodynamics, where fallacious concepts like 'phlogiston' were rapidly disproved by energetic researchers such as Lavoisier in the late 18th century, relatively little understanding of tribology was gained until 1886 with the publication of Osborne Reynolds' classical paper on hydrodynamic lubrication. Reynolds proved that hydrodynamic pressure of liquid entrained between sliding surfaces was sufficient to prevent contact between surfaces even at very low sliding speeds. His research had immediate practical application and lead to the removal of an oil hole from the load line of railway axle bearings. The oil, instead of being drained away by the hole, was now able to generate a hydrodynamic film and much lower friction resulted. The work of Reynolds initiated countless other research efforts aimed at improving the interaction between two contacting surfaces, and which continue to this day. As a result journal bearings are now designed to high levels of sophistication. Wear and the fundamentals of friction are far more complex problems, the experimental investigation of which is dependent on advanced instrumentation such as scanning electron microscopy. Therefore, it has only recently been possible to study these processes on a microscopic scale where a true understanding of their nature can be found. Tribology is therefore a very new field of science, most of the knowledge being gained after the Second World War. In comparison many basic
  2. 2. RECENT ADVANCES IN TRIBOLOGY Page 2 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki engineering subjects, e.g. thermodynamics, mechanics and plasticity, are relatively old and well established. Tribology is still in an imperfect state and subject to some controversy which has impeded the diffusion of information to technologists in general. The need for information is nevertheless critical; even simple facts such as the type of lubricant that can be used in a particular application, or preventing the contamination of oil by water must be fully understood by an engineer. As our technological civilization expands, material and energy conservation is becoming increasingly important. Wear is a major cause of material wastage, so any reduction of wear can effect considerable savings. Friction is a principal cause of energy dissipation and considerable savings are possible by improved friction control. Lubrication is the most effective means of controlling wear and reducing friction. Thus tribology, which is the science and technology of wear of friction, lubrication and wear, is of considerable importance in material and energy conservation. The history of this relatively new science which is concerned with problems that have always presented man with a challenge has been recorded, and the fundamentals reviewed. 1.2 MEANING OF TRIBOLOGY Tribology, which focuses on friction, wear and lubrication of interacting surfaces in relative motion, is a new field of science defined in 1967 by a committee of the Organization for Economic Cooperation and Development. Tribology’ is derived from the Greek word ‘tribos’ meaning rubbing or sliding. After an initial period of scepticism as is inevitable for any newly introduced word or concept, the word ‟tribology‟ has gained gradual acceptance. As the word tribology is relatively new, its meaning is still unclear to the wider community and humorous comparisons with tribes or tribolites tend to persist as soon as the word „tribology‟ is mentioned. Wear is the major cause of material wastage and loss of mechanical performance and any reduction in wear can result in considerable savings. Friction is a principal cause of wear and energy dissipation. Considerable savings can be made by improved friction control. It is estimated that one third of the world‟s energy resources in present use is needed to overcome friction in one form or another. Lubrication is an effective means of controlling wear and reducing friction. Tribology is a field of science which applies an operational analysis to
  3. 3. RECENT ADVANCES IN TRIBOLOGY Page 3 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki problems of great economic significance such as reliability, maintenance and wear of technical equipment ranging from household appliances to spacecraft.
  4. 4. RECENT ADVANCES IN TRIBOLOGY Page 4 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 2.PRACTICAL OBJECTIVES OF TRIBOLOGY Film formation between any pair of sliding objects is a natural phenomenon which can occur without human intervention. Film formation might be the fundamental mechanism preventing the extremely high shear rates at the interface between two rigid sliding objects. Non-mechanical sliding systems provide many examples of this film formation. For example, studies of the movement between adjacent geological plates on the surface of the earth reveal that a thin layer of fragmented rock and water forms between opposing rock masses. Chemical reactions between rock and water initiated by prevailing high temperatures (about 6OOOC) and pressures (about 100 [MPa]) are believed to improve the lubricating function of the material in this layer 131. Laboratory tests of model faults reveal that sliding initiates the formation of a self-sliding layer of fragmented rock at the interface with solid rock. A pair of self-sealing layers attached to both rock masses prevent the leakage of water necessary for the lubricating action of the inner layer of fragmented rock and water [31. Although the thickness of the intervening layer of fragmented rock is believed to be between 1 - 100 [m] , this thickness is insignificant when compared to the extent of geological plates and these layers can be classified as „films‟. Sliding on a geological scale is therefore controlled by the properties of these „lubricating films‟, and this suggests a fundamental similarity between all forms of sliding whether on the massive geological scale or on the microscopic scale of sliding between erythrocytes and capillaries. The question is, why do such films form and persist? A possible reason is that a thin film is mechanically stable, i.e. it is very difficult to completely expel such a film by squeezing between two objects. It is not difficult to squeeze out some of the film but its complete removal is virtually impossible. Although sliding is destructive to these films, i.e. wear occurs, it also facilitates their replenishment by entrainment of a 'lubricant' or else by the formation of fresh film material from wear particles. Film formation between solid objects is intrinsic to sliding and other forms of relative motion, and the study and application of these films for human benefits is the raison d 'etre of tribology.
  5. 5. RECENT ADVANCES IN TRIBOLOGY Page 5 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki In simple terms it appears that the practical objective of tribology is to minimize the two main disadvantages of solid to solid contact: friction and wear, but this is not always the case. In some situations, as illustrated in Figure 1.1, minimizing friction and maximizing wear or minimizing wear and maximizing friction or maximizing both friction and wear is desirable. For example, reduction of wear but not friction is desirable in brakes and lubricated clutches, reduction of friction but not wear is desirable in pencils, increase in both friction and wear is desirable in erasers.
  6. 6. RECENT ADVANCES IN TRIBOLOGY Page 6 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 3. FRICTION The friction force is the resistance encountered when one body moves relative to another body with which it is in contact. The static friction force is how hard you have to push something to make it, whilst the dynamic friction force is how hard you push to keep it moving. The ratio of the frictional force F to the normal force W is called the co-efficient of friction and given the Greek symbol m (pronounced mew). Friction is the dissipation of energy between sliding bodies. Four basic empirical laws of friction have been known for centuries since the work of da Vinci and Amonton: the tangential friction force is proportional to the normal force in sliding; there is a proportionality between the maximum tangential force before sliding and the normal force when a static body is subjected to increasing tangential load; friction force is independent of the contact area; friction force is independent of the sliding speed. In the early studies of contacts between the real surfaces it was assumed that since the contact stresses between asperities are very high the asperities must deform plastically . This assumption was consistent with Amonton's law of friction, which states that the friction force is proportional to the applied load, providing that this force is also proportional to the real contact area. However, it was later shown that the contacting asperities after an initial plastic deformation attain a certain shape after which the deformation is elastic. It has been demonstrated on a model surface made up of large irregularities approximated by spheres with superimposed smaller set of spheres which were supporting an even smaller set , that the relationship between load and contact area is almost linear despite the contact being elastic. It was found that a nonlinear increase in area with load at an individual contact is compensated by the increasing number of contacts. A similar tendency was also found for real surfaces with random topography. It therefore became clear that Amonton‟s law of friction is also consistent with elastic deformations
  7. 7. RECENT ADVANCES IN TRIBOLOGY Page 7 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki taking place at the asperities providing that the surface exhibits a complex hierarchical structure so that several scales of microcontact can occur. The proportionality between friction force and normal load has lead to the definition of ‘kinetic’ and ‘static’ coefficients of friction. In many reference books, coefficients of friction are quoted as ‟properties‟ of certain combinations of materials. This approach, however, is very simplistic since the coefficients of friction are dependent on parameters such as temperature and sliding speed and in some instances there is no exact proportionality between friction force and normal load. The underlying reasons for the laws of friction listed above have only recently been deduced. It has been found that much of the characteristics of friction are a result of the properties of rough surfaces in contact.
  8. 8. RECENT ADVANCES IN TRIBOLOGY Page 8 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 4.WEAR Wear may be defined as the undesired displacement or removal of surface material, although under some circumstances, the initial stages of wear or mild wear which tends to smooth surfaces, may be beneficial for the running-in of mechanisms. The economic implications of wear cause concern in industry, as a reasonable life is required of mechanical equipment to cover capital and maintenance costs. It certainly causes a great deal of expenditure on maintenance t h a t must take place; such maintenance is costly in itself , but also costly in lost productivity whilst it is being carried out. Progress i n wear control and prevention can be made only after a better understanding of the mechanisms by which it occurs and of the controlling factors has been acquired. TYPES OF WEAR ABRASIVE WEAR EROSIVE WEAR CAVITATION WEAR 1. ABRASIVE WEAR It was originally thought that abrasive wear by grits or hard asperities closely resembled cutting by a series of machine tools or a file. However, microscopic examination has revealed that the cutting process is only approximated by the sharpest of grits and many other more indirect mechanisms are involved. The particles or grits may remove material by microcutting, microfracture, pull-out of individual grains or accelerated fatigue by repeated deformations as illustrated.
  9. 9. RECENT ADVANCES IN TRIBOLOGY Page 9 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki Fig :- Mechanisms of abrasive wear: microcutting, fracture, fatigue and grain pull-out. 2. EROSIVE WEAR Erosive wear involves several wear mechanisms which are largely controlled by the particle material, the angle of impingement, the impact velocity, and the particle size. If the particle is hard and solid then it is possible that a process similar to abrasive wear will occur. Where liquid particles are the erodent, abrasion does not take place and the wear mechanisms involved are the result of repetitive stresses on impact. The term 'erosive wear' refers to an unspecified number of wear mechanisms which occur when relatively small particles impact against mechanical components. This definition is empirical by nature and relates more to practical considerations than to any fundamental understanding of wear. The known mechanisms of erosive wear are illustrated.
  10. 10. RECENT ADVANCES IN TRIBOLOGY Page 10 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki Fig :- Possible mechanisms of erosion; a) abrasion at low impact angles, b) surface fatigue during low speed, high impingement angle impact, c) brittle fracture or multiple plastic deformation during medium speed, large impingement angle impact, d) surface melting at high impact speeds, e) macroscopic erosion with secondary effects, f) crystal lattice degradation from impact by atoms.
  11. 11. RECENT ADVANCES IN TRIBOLOGY Page 11 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 3. CAVITATION WEAR The characteristic feature of cavitation is the cyclic formation and collapse of bubbles on a solid surface in contact with a fluid. Bubble formation is caused by the release of dissolved gas from the liquid where it sustains a near-zero or negative pressure. Negative pressures are likely to occur when flow of liquid enters a diverging geometry, i.e. emerging from a small diameter pipe to a large diameter pipe. The down-stream face of a sharp sided object moving in liquids, e.g. ship propeller, is particularly prone to cavitation. The ideal method of preventing cavitation is to avoid negative pressures close to surfaces, but in practice this is usually impossible. When a bubble collapses on a surface the liquid adjacent to the bubble is at first accelerated and then sharply decelerated as it collides with the surface. The collision between liquid and solid generates large stresses which can damage the solid. Transient pressures as high‟as 1.5 [GPa] are possible. The process of bubble collapse together with experimental evidence of a hole formed in a metal surface by bubble collapse are shown in Figure. Fig :- Mechanism of cavitation wear; mechanism of bubble collapse
  12. 12. RECENT ADVANCES IN TRIBOLOGY Page 12 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 5. LUBRICATION Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity. Types of lubrication :- HYDROSTATIC LUBRICATION ELASTOHYDRODYNAMIC LUBRICATION EXTREME PRESSURE LUBRICATION SOLID LUBRICATION HYDROSTATIC LUBRICATION In hydrostatic lubrication the bearing surfaces are fully separated by a lubricating film of liquid or gas forced between the surfaces by an external pressure. The pressure is generated by an external pump instead of by viscous drag as is the case with hydrodynamic lubrication. As long as a continuous supply of pressurized lubricant is maintained, a complete film is present even at zero sliding speed. Hydrostatic films usually have a considerable thickness reaching 100 [pm] and therefore prevent contact between the asperities of even the roughest surfaces. This ensures a complete absence of sticking friction. Furthermore, the friction generated by viscous shear of the lubricant decreases to zero at zero sliding speed. Hydrostatic bearings can support very large masses and allow them to be moved from their stationary positions with the use of minimal force. These extraordinary features of zero static friction and high load capacity were applied, for example, in the 5.08 [ml diameter Mount Palomar telescope and in many radar installations. With other types of bearing, starting friction is inevitable and can cause distortion and damage to large structures. This problem is critical to the design of large telescopes which rely on extreme accuracy of telescope positioning. ELASTOHYDRODYNAMIC LUBRICATION Elastohydrodynamic lubrication can be defined as a form of hydrodynamic lubrication where the elastic deformation of the contacting bodies and the changes of viscosity with pressure play
  13. 13. RECENT ADVANCES IN TRIBOLOGY Page 13 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki fundamental roles. The influence of elasticity is not limited to second-order changes in load capacity or friction as described for pivoted pad and journal bearings. Instead, the deformation of the bodies has to be included in the basic model of elastohydrodynamic lubrication. The same refers to the changes in viscosity due to pressure. Elastohydrodynamic lubrication can be defined as a form of hydrodynamic lubrication where the elastic deformation of the contacting bodies and the changes of viscosity with pressure play fundamental roles. The influence of elasticity is not limited to second-order changes in load capacity or friction as described for pivoted pad and journal bearings. Instead, the deformation of the bodies has to be included in the basic model of elastohydrodynamic lubrication. The same refers to the changes in viscosity due to pressure. EXTREME PRESSURE LUBRICATION In many practical applications there are cases where the operating conditions are such that neither hydrodynamic nor EHL lubrication is effective. The question then is, how are the interacting machine components lubricated and what is the lubrication mechanism involved? The traditional name for this type of lubrication is 'boundary lubrication' or 'boundary and extreme-pressure lubrication'. Several specialized modes of lubrication such as, adsorption, surface localized viscosity enhancement, amorphous layers and sacrificial films are commonly involved in this lubrication regime to ensure the smooth-functioning and reliability of machinery. Boundary and E.P. lubrication is a complex phenomenon. The lubrication mechanisms involved can be classified in terms of relative load capacity and limiting frictional temperature. These lubrication mechanisms are usually controlled by additives present in the oil. Since the cost of a lubricant additive is usually negligible compared to the value of the mechanical equipment, the commercial benefits involved in this type of lubrication can be quite large. SOLID LUBRICATION Solid lubricants have many attractive features compared to oil lubricants, and one of the obvious advantages is their superior cleanliness. Solid lubricants can also provide lubrication at extremes of temperature, under vacuum conditions, or in the presence of strong radioactivity. Oil usually cannot be used under these conditions. Solid lubrication is not new, the use of graphite as a
  14. 14. RECENT ADVANCES IN TRIBOLOGY Page 14 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki forging lubricant is a traditional practice. The scope of solid lubrication has, however, been greatly extended by new technologies for depositing the solid film onto the wearing surface. The lubricant deposition method is critical to the efficiency of the lubricating medium, since even the most powerful lubricant will be easily scraped off a wearing surface if the mode of deposition is incorrect. Specialized solid substances can also be used to confer extremely high wear resistance on machine parts. The economics of manufacture are already being transformed by the greater lifetimes of cutting tools, forming moulds, dies, etc. The wear resistant substances may be extremely expensive in bulk but when applied as a thin film, they provide an economical and effective means of minimizing wear problems. Fig :- Mechanism of lubrication by lamellar solids RECENT ADVANCES IN TRIBOLOGY The below mentioned advances are the most recent developments achieved in the field of tribology which will be discussed in detail later in this report
  15. 15. RECENT ADVANCES IN TRIBOLOGY Page 15 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 1. SOYBEAN OIL AS FUTURE LUBRICANT FOR IC ENGINES. 2. CHEMICAL VAPOR DEPOSITION (CVD) 3. CHEMICAL VAPOR DEPOSITION (CVD) 4. TRIBOLOGY CONCERNS IN MEMS DEVICES 5. DIAMOND COATING 6. ULTRANANOCRYSTALLINE DIAMOND (UNCD) 7. SELF ASSEMBLED MONOLAYERS (SAMS) 8. CANTILEVER BEAM ARRAY TECHNIQUE 1. SOYBEAN OIL AS FUTURE LUBRICANT FOR IC ENGINES Using plant-derived oils like soybean oil as a form of lubrication is nothing new to companies that operate and maintain machinery. The idea of using soy as a replacement for petroleum has been around for decades and is becoming increasingly important due to volatile petroleum prices and heightened concern with dependency on foreign sources of petroleum. Soy also adds natural lubrication to machinery and enhances engine performance. Soybean oil is a vegetable oil extracted from soybean seeds. It is easily available at low prices. PROPERTIES OF SOYBEAN OIL It has a high viscosity index up to 223. Has comparatively high flash point 610°F. Has good fire point about 650°F. It has high pour point, it can be reduced by winterizing the soybean oil. MERITS OF SOYBEAN OIL Soybean oil is biodegradable, in general it is less toxic. It is a renewable oil, so it reduces dependency of foreign petroleum products. Ease of processing. 2. CHEMICAL VAPOR DEPOSITION
  16. 16. RECENT ADVANCES IN TRIBOLOGY Page 16 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki Chemical vapor deposition (CVD) is a chemical process used to produce high-purity, high- performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or morevolatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. CVD is practiced in a variety of formats. These processes generally differ in the means by which chemical reactions are initiated. 1. Classified by operating pressure: Atmospheric pressure CVD (APCVD) – CVD process at atmospheric pressure. Low-pressure CVD (LPCVD) – CVD process at sub-atmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer. Ultrahigh vacuum CVD (UHVCVD) – CVD process at very low pressure, typically below 10−6 Pa (~10−8 torr). Note that in other fields, a lower division between high and ultra-high vacuum is common, often 10−7 Pa. Most modern CVD processes are either LPCVD or UHVCVD. 2. Classified by physical characteristics of vapor: Aerosol assisted CVD (AACVD) – A CVD process in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically. This technique is suitable for use with non-volatile precursors. Direct liquid injection CVD (DLICVD) – A CVD process in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors (typically car injectors). The precursor vapors are then transported to the substrate as in classical CVD process. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique. APPLICATION
  17. 17. RECENT ADVANCES IN TRIBOLOGY Page 17 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki Integrated circuits, electronic devices and sensors. Catalysts Micromachines, fine powder and ceramic powder protective coatings. Thin film is formed from gas phase components
  18. 18. RECENT ADVANCES IN TRIBOLOGY Page 18 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki
  19. 19. RECENT ADVANCES IN TRIBOLOGY Page 19 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 3. PHYSICAL VAPOR DEPOSITION Physical vapor deposition (PVD) is a variety of vacuum deposition methods used to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces (e.g., onto semiconductor wafers). The coating method involves purely physical processes such as high temperature vacuum evaporation with subsequent condensation, or plasma sputter bombardment rather than involving a chemical reaction at the surface to be coated as in chemical vapor deposition. The term physical vapor deposition originally appeared in the 1966 book Vapor Deposition by C. F. Powell, J. H. Oxley and J. M. Blocher Jr., (but Michael Faraday was using PVD to deposit coatings as far back as 1838). Variants of PVD include Cathodic Arc Deposition: In which a high power electric arc discharged at the target (source) material blasts away some into highly ionized vapor to be deposited onto the workpiece. Electron beam physical vapor deposition: In which the material to be deposited is heated to a high vapor pressure by electron bombardment in "high" vacuum and is transported by diffusion to be deposited by condensation on the (cooler) workpiece. Evaporative deposition: In which the material to be deposited is heated to a high vapor pressure by electrically resistive heating in "low" vacuum. Pulsed laser deposition: In which a high power laser ablates material from the target into a vapor. Sputter deposition: In which a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor for subsequent deposition.
  20. 20. RECENT ADVANCES IN TRIBOLOGY Page 20 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki APPLICATIONS Aerospace Automotive Surgical/Medical Dies and moulds for all manner of material processing Cutting tools Fire arms
  21. 21. RECENT ADVANCES IN TRIBOLOGY Page 21 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 4. TRIBOLOGY CONCERNS IN MEMS DEVICES Because of large surface-to-volume ratios and low restoring forces, unwanted adhesion and friction can dominate the performance of microelectromechanical systems (MEMS) devices. To guarantee the function and reliability of MEMS devices, tribologists must understand the origins of adhesion, friction, and wear over a broad range of length scales from the macroscopic to the molecular. In this article, we present an overview of challenges, successes, and initial steps toward a fundamental understanding. Since failure of MEMS devices is dependent on the tribology of the structures in the system. To decrease the occurrences of failures from these means, materials considerations are described that reduce the adhesion and friction to the system structures. This helps to decrease the wear and asperity formation at the surfaces in the devices. There are two ways that materials can be utilized in this manner. One is to use new materials in the fabrication steps that are tough and resilient, whereby helping to prevent material failure. There are many materials that fall into this category, such as diamond like carbon (DLC), tungsten and titanium carbide. The second way is to coat the silicon based structures with organic molecules that act as a barrier between the structures and help to create a lubricating layer so that the structures don‟t wear away as quickly. The most typical organic layer is a self assembled monolayer (SAM) that covalently bonds to the silicon. These new materials will help to correct many of the MEMS failure issues and produce more applications for them. Friction and Wear are the biggest issues in blocking advances of MEMS technology. Once SAMS and Diamond Coatings are more fully developed, MEMS technology will be able to more completely realize its potential.
  22. 22. RECENT ADVANCES IN TRIBOLOGY Page 22 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 5. DIAMOND COATINGS QQC, a revolutionary process, can deposit a uniform layer of diamond on almost any type of material ranging from glass and plastic to metals. It is done using the carbon dioxide from the air as the carbon source and subjecting it to a combination of lasers to do in seconds what takes conventional chemical vapor deposition (CVD) processes hours. This relatively new laser process creates pure diamond and bonds it to a surface of a material with the ease of paint on a brush. BREAKTHROUGH IN DIAMOND COATING A major breakthrough in diamond deposition technology occurred when Pravin Mistry, a metallurgist was doing independent materials research and consulting to industries requiring better tooling for metal forming and extrusion. He was working towards fabricating hard materials, using lasers to synthesize ceramics and metal-matrix composites (MMC) on aluminium extrusion dies to improve their performance and longevity. In a fortunate misstep during laser synthesis of titanium diboride, Mistry switched carbon dioxide for nitrogen and produced a coating speckled with some black particulate inclusions. Analysis of the coating's surface indicated the presence of polycrystalline diamond. The QQC Diamond coating process uses the carbon dioxide from the atmosphere as
  23. 23. RECENT ADVANCES IN TRIBOLOGY Page 23 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki the carbon source and subjects it to multiplexed lasers to produce diamond film that can be deposited ontoalmost any material. THE QQC PROCESS Briefly describing the process it consists of:  Laser energy directed at a substrate to mobilize, vaporize and react a constituent (primary) element (e.g., carbon) contained within the substrate. This changes the crystalline structure of the basic element, and spreads a coating on the material. This results in diffusion bonding of the coating to the material.  The laser energy is provided by a combination of different lasers. The output beams are directed through a nozzle delivering the secondary element to the reaction zone. The reaction zone is shielded by a non-reactive shielding gas delivered through the nozzle. A flat plasma is created by the lasers, constituent element and secondary element on the surface of the substrate to create the coating. Certain advantageous metallurgical changes are created in the substrate due to the pretreatment. The processes are suitably performed in ambient, without preheating the substrate and without a vacuum. The QQC approach creates diamond in an ordinary atmosphere, not the high-temperature vacuum used in standard diamond manufacture. Multiple laser beams are directed through a cloud of carbon dioxide at a tungsten carbide surface. The lasers break the carbon dioxide into oxygen and carbon. Diamond is formed from the bonding of this carbon with carbon atoms that the laser energy has put into motion from the rotating surface of the object. ADVANTAGES OF QCC PROCESS
  24. 24. RECENT ADVANCES IN TRIBOLOGY Page 24 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki Key advantages of the QQC system's process over existing technology include: • Superior adhesion and reduced stress result from a metallurgical bond between the diamond and substrate. • The process is carried out in atmosphere, without the restrictions of a vacuum chamber. Almost any size or shape can be coated by controlling movements of the lasers or workpiece. • Pretreatment and/or preheating of the substrate is not required, permitting coating of the substrate of as-manufactured components and elimination of wet chemistry pretreatment. • Only carbon dioxide is used as a primary/secondary source for carbon with nitrogen acting as a shield and possible stockpiling process ingredient. This replaces the use of dangerous gases such as hydrogen and methane, critical ingredients in the CVD process. • Deposition rates are dramatically increased, with linear growth rates exceeding 1 micron per second as opposed to 1 to 5 microns per hour by CVD. • The process can be applied to almost any substrate such as stainless steel, high-speed steel, iron, plastic, glass, copper, aluminum, titanium and silicon.
  25. 25. RECENT ADVANCES IN TRIBOLOGY Page 25 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki
  26. 26. RECENT ADVANCES IN TRIBOLOGY Page 26 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 6. ULTRANANOCRYSTALLINE DIAMOND (UNCD) UNCD Wafers are wafer-scale diamond products used for MEMS development, tribological testing, and unique nano-scale processing applications. UNCD Wafers offer the ability to create and experiment with the extraordinary properties of diamond using the award winning family of UNCD materials. UNCD Wafers meet a set of baseline wafer-level specifi cations for thickness and property uniformity, wafer bow, and particle counts suitable for direct insertion into a MEMS foundry process sequence. It is a better method of producing diamond-like films of grain size 2- 5nm. Unlike conventional diamond film CVD, C60 is introduced into the reaction along with CH4. C60 collides with itself, creating C2 (carbon “dimers”) These C2 molecules enter the diamond lattice. An abundance of C2 is the goal of the UNCD creation process.
  27. 27. RECENT ADVANCES IN TRIBOLOGY Page 27 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 7. SELF ASSEMBLED MONOLAYERS (SAMS) Self assembled monolayers are recent additions to the family of molecular films. These films are different from L–B films because they are self assembled to form an ordered molecular film, unlike L–B where they are transferred from the air-liquid interface to the surface. The SA monolayers are thus defined as molecular assemblies which form spontaneously by the immersion of a surface into a solution of surfactant. Thus depending on the surfactant and the substrate, monolayers vary. The most common monolayers are formed with organosilicon derivatives, alkane thiols, dialkylsulphides, alcohols, amines and carboxylic acids on different surfaces. All molecules will not self organise on all substrates. The affinity between the molecule and the surface is an important factor. From a number of investigations, it is now clear that the first event in self organisation is the chemical bonding of the surface active group (the head group) to a surface site. It so happens that since the chemical formation reaction is highly exothermic, all the available surface sites are occupied. Since the kind of binding brings the molecules close to each other, the short range van der Waals forces become important. These interactions make the molecular chains attached to the head group stand up vertically, although with a tilt. An assembly of these molecules can extend over several hundreds of angstroms and an ordered oriented monomolecular layer results.  Two Types • Silane – deposits on silicon
  28. 28. RECENT ADVANCES IN TRIBOLOGY Page 28 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki • Thiol – deposits on gold  Deposition Formations • Densely Packed • Amorphous Structure  Functional group determines: • applications • hydrophilicity/hydrophobicity  Used as: • binders for subsequent molecules • lubricants  Common hydrophobic SAMS: • OTS (long chain hydrocarbon) • FDTS (long chain fluorocarbon)
  29. 29. RECENT ADVANCES IN TRIBOLOGY Page 29 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki
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  31. 31. RECENT ADVANCES IN TRIBOLOGY Page 31 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 8. CANTILEVER BEAM ARRAY TECHNIQUE • Cantilever beams are fabricated of different lengths • Cantilevers are put into contact with surface • Longer beams adhere to surface • Longest beam that does not stick signifies adhesion force • SAM coated beams adhere after longer lengths than oxide surface 9. ECONOMIC ASPECTS OF TRIBOLOGY
  32. 32. RECENT ADVANCES IN TRIBOLOGY Page 32 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki The Lubrication Report estimated, within an error of twenty-five per cent, that an amount exceeding five hundred million pounds per annum can be saved in the civilian sector of the UK economy by improvements in education and research in tribology . Such improvements are significant , not merely in cost savings, but are crucial to technological progress and have doubly significant implications for the economic well-being of the nation and the reputation of its engineering products. The ASME Research Committee on Lubrication in their "Strategy for Energy Conservation through Tribology" reported the magnitudes of energy conservation that can potentially be obtained in the four major areas of road transportation , power generation, turbo machinery and industrial processes through progress in tribology . The estimated 11 per cent total savings in annual US energy consumption is equivalent to some sixteen billion US dollars by an expenditure in research and development of an estimated twenty-four million dollars. A techno-economic study concluded that the application of tribological principles and practices can effect national energy savings of considerable magnitude in the United Kingdom, in the areas covered which comprise the major parts of 87% of energy consumption. These savings are estimated at €468 to f700 million per annum. Erosion can be expensive and it has been reported that the ingestion of dust clouds can reduce the lives of helicopter engines by as much as 90 per cent; local stall can be caused by removal of as little as 0.05 mm of material from the leading edges of compressor blades. In pneumatic transportation of material through pipes, the erosive wear a t bends can be up to fifty times more than that in straight sections. Even wood chips can cause such wear. Analyses of the failure of boiler tubes indicate that about one third of all occurrences were due to erosion. Although abrasive wear is useful to shape and Polish engineering components, its unwanted occurrence is probably the most serious industrial wear problem. In the agricultural industry as many as forty percent of the components replaced on equipment have failed by abrasive wear. The wear of tools used for cutting metals is of considerable importance to the economics o f the engineering industry, It was estimated in 1971 that forty billion dollars was spent in the USA on the machining of metal parts. In the UK about twenty million carbide cutting tools are used per year at a cost of fifty million pounds.
  33. 33. RECENT ADVANCES IN TRIBOLOGY Page 33 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki Several estimates have been made on the cost of friction and wear. Jost stated that friction and wear in the USA accounted for an expenditure of one hundred billion dollars per annum. A Committee of the Ministry of Research and Technology of F.R.G. estimated that friction and wear caused a national economic waste of ten billion OM per annum of which about fifty per cent is due to abrasive wear. Rabinowicz has estimated that about ten per cent of all energy generated by man is dissipated in friction processes. Tribological failures are in variably associated with bearings and to illustrate the costs which can be involved it has been reported that a simple bearing failure in a fully integrated steel mill can lead to a total shut down which at full output rate may cost one hundred and fifty to three hundred pounds per minute. A similar bearing failure on a modern generator set could involve the Central Electricity Generating Board in a loss of one to twenty pounds sterling per minute till the set was again operational . A similar bearing failure in the USA has been quoted to cost twenty - five thousand dollars per day. It has been reported that the total cost of wear for a US naval aircraft amounted to two hundred and forty three dollars per flight hour.
  34. 34. RECENT ADVANCES IN TRIBOLOGY Page 34 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki 10.IMPACT OF TRIBOLOGY Since the publication of the Lubrication Report there has been an increasing awareness throughout industry of the subject of tribology .In the UK the National Centre for Tribology and Industrial Units of Tribology have been set up to provide advice to industry on the utilisation of existing knowledge. These are now viable establishments operating as contract research organisations selling their services at commercial rates. Over thirty universities polytechnics and technical colleges have incorporated courses on various aspects of tribology into their syllabuses. A basic tribology module for undergraduate mechanical engineering courses has been drawn up. Tribology is an elective subject for the higher national certificate (H.N.C.) in engineering in the United Kindom and a tribology content is included in some committee for national academic awards (C.N.N.A.) courses. Post-graduate research in tribology , leading to higher degrees is carried out at several universities ; three have chairs in tribology. Various courses and training programmed are also available to industry. Tribology is now recognized u n i v e r s a l l y and President Carter of U.S.A. Declared it to be a generic technology underlying many industrial sections and the prospectus for an Industrial Tribology Institute at Rensselaer Technology Center has been presented. Numerous papers on tribology are published annually and many report research directed towards a better understanding of the fundamental principles governing interacting surfaces. Unfortunately, most of the information provided is not suitable for direct use by designers and engineers as research workers generally find it more convenient to express results in terms of non-dimensional parameters rather than as the specific data required for design purposes. A tribology handbook has been produced with the object of providing information to industry in a form that is readily accessible and understood by engineering designers, draughtsmen and works engineers. A synoptic journal has been introduced to reduce time spent in literature perusal.
  35. 35. RECENT ADVANCES IN TRIBOLOGY Page 35 of 35 Department of Mechanical Engineering Bheemanna Khandre Institute Of Technology, Bhalki

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