Report on advances in tribology

RECENT ADVANCES IN TRIBOLOGY Page 1 of 35

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

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



problems of great economic significance such as reliability, maintenance and wear of technical

equipment ranging from household appliances to spacecraft.



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.

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.

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

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.



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.

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.



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.



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



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

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

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

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

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


http://en.wikipedia.org/wiki/Semiconductor_industry

http://en.wikipedia.org/wiki/Chemical_process


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

Integrated circuits, electronic devices and sensors.

Catalysts


http://en.wikipedia.org/wiki/Ultra-high_vacuum

http://en.wikipedia.org/wiki/Torr

http://en.wikipedia.org/wiki/Pascal_(unit)

http://en.wikipedia.org/wiki/By-product

http://en.wikipedia.org/wiki/Chemical_decomposition

http://en.wikipedia.org/wiki/Chemical_reaction

http://en.wiktionary.org/wiki/precursor

http://en.wikipedia.org/wiki/Volatility_(chemistry)

http://en.wikipedia.org/wiki/Wafer_(electronics)

http://en.wikipedia.org/wiki/Thin_film


Micromachines, fine powder and ceramic powder protective coatings.

Thin film is formed from gas phase components



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.


http://en.wikipedia.org/wiki/Cathodic_Arc_Deposition

http://en.wikipedia.org/wiki/Michael_Faraday

http://en.wikipedia.org/wiki/Chemical_vapor_deposition

http://en.wikipedia.org/wiki/Evaporation

http://en.wikipedia.org/wiki/Wafer_(electronics)

http://en.wikipedia.org/wiki/Semiconductor

http://en.wikipedia.org/wiki/Thin_film

http://en.wikipedia.org/wiki/Vacuum_deposition


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.

APPLICATIONS

Aerospace

Automotive

Surgical/Medical

Dies and moulds for all manner of material processing

Cutting tools

Fire arms


http://en.wikipedia.org/wiki/Sputter_deposition

http://en.wikipedia.org/wiki/Pulsed_laser_deposition

http://en.wikipedia.org/wiki/Evaporation_(deposition)

http://en.wikipedia.org/wiki/Electron_beam_physical_vapor_deposition


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.

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

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

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.



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.



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

• 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)




O O O OSi Si Si SiO O O OSi Si Si SiO O OO O O OSi Si Si SiOHOHOHOH

Deposition






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



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.



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.



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.


