14

CHAPTER 2

SURFACE MODIFICATION TECHNIQUES

2.1INTRODUCTION

The selection of technology to engineer the surface is an integral part

of an engineering component design. The first step in surface modification

technique to determine the surface and substrate engineering requirements which

involves one or more of the properties like wear resistance, corrosion and

erosion resistance and thermal resistance, fatigue, creep strength, pitting

resistance etc.The various surface treatments generally used in engineering

practice and presented as under.

2.2 SURFACE MODIFICATION METHODS/ TECHNIQUES

A simplified classification of various groupings of non-mechanical

surface treatments could be reduced as

1. Thermal treatments 2.Thermo-chemical treatment 3.Plating and coating

4. Implantation

The figure 2.1, illustrates different types of surface treatments and

typical thickness of engineered surface materials produced by them. The

effectiveness depends on particular surface and modification technique.

1. PVD process 2.CVD process 3.Electoless Nickel 4.Composite 5.Thermal

spraying 6. Surface welding 7. Ion Implantation 8. Anodising 9. Boronizing

10. Nitriding 11. Carbonitriding 12. Carburizing 13.Nitrocarburising 14. Surface

alloying 15. Thermal hardening.

15

Numerous processes are used for surface treatments, based on

mechanical, chemical, thermal and physical. Their principles and characteristics

are obtained as follows:

There are two categories of vapor deposition processes: physical

vapor deposition (PVD) and chemical vapor deposition (CVD). In PVD

processes, the work piece is subjected to plasma bombardment. In CVD

processes, thermal energy heats the gases in the coating chamber and drives the

deposition reaction.

Fig.2.1 Typical thickness of engineered surface layers Physical Vapour

Deposition

In this process, the work piece or substrate is subjected to high

temperature vacuum evaporation or plasma sputter bombardment to deposit thin

films by the condensation of a vaporized form of the material onto substrate

16

surfaces. This process contains the three major techniques; evaporation,

sputtering and ion plating. It produces a dense, hard coating. The primary PVD

methods are.ion plating, ion implantation, sputtering and laser surface alloying.

Fig.2.2. PVD process using Plasma Fig.2.3. PVD process using arc

evaporation sputtering

PVD is used in the manufacture of semiconductor wafers, aluminized

PET film for snack bags and balloons, cutting tools for metalworking and

generally used for extreme thin films like atomic layers and mostly for small

substrates.

Chemical Vapour Deposition (CVD)

In these processes, thermal energy heats the gases in the coating

chamber and drives the deposition reaction and then this reactant gas mixture

(mixture of gas precursors and coating material also known as a reactive vapour)

17

impinges on the substrate. CVD processes can be used to deposit coating

materials, form foils, powders, composite materials in the shape of spherical

particles, filaments, and whiskers and also in structural applications, optical,

chemical, photovoltaic and electronics.. Start-up costs are typically very

expensive. CVD includes sputtering, ion plating, plasma-enhanced CVD, low-

pressure CVD, laser-enhanced CVD, active-reactive evaporation, ion beam, laser

beam evaporation, and many other variations. These variants are distinguished by

the manner in which precursor gases are converted into the reactive gas mixtures.

It is usually in the form of a metal halide, metal carbonyl, a hydride,

or an organ metallic compound. The precursor may be in gas, liquid, or solid

form. Gases are delivered to the chamber under normal temperatures and

pressures, whereas solids and liquids require high temperatures and/or low

pressures in conjunction with a carrier gas. Once in the chamber, energy is

applied to the substrate to facilitate the reaction of the precursor material upon

impact. The ligand species is liberated from the metal species to be deposited

upon the substrate to form the coating. Because most CVD reactions are

endothermic, the reaction may be controlled by regulating the amount of energy

input.

Disadvantages of CVD, the precursor chemicals should not be toxic,

and exhaust system should be designed to handle any reacted and unreacted

vapors that remain after the coating process is complete. Other waste effluents

from the process must be managed appropriately. Retrieval, recycle, and disposal

methods are dictated by the nature of the chemical. For example, auxiliary

chemical reactions must be performed to render toxic or corrosive materials

harmless, condensates must be collected.

18

Fig.2.4. Schematic diagram of CVD process

Electroless nickel plating

Electroless nickel (EN) plating is a chemical reduction process that

depends upon the catalytic reduction process of nickel ions in solution containing

a chemical reducing agent and water and the subsequent deposition of nickel

metal without the use of electrical energy. Thus in the EN plating process, the

driving force for the reduction of nickel metal ions and their deposition is

supplied by a chemical reducing agent in solution. This driving potential is

essentially constant at all points of the surface of the component, provided the

agitation is sufficient to ensure a uniform concentration of metal ions and

reducing agents. The electro less deposits are therefore very uniform in thickness

all over the part’s shape and size. The process is advantageous when plating

complex shape devices, holes, recesses, internal surfaces, valves, threaded parts

etc. Electroless (autocatalytic) nickel coating provides a hard, uniform, corrosion,

abrasion, and wear-resistant surface to protect machine components in many

industrial environments. EN is chemically deposited, making the coating

exceptionally uniform in thickness. If carefully process is controlled good

surface finish can be produced which eliminates costly machining after plating.

19

In a true electroless plating process, reduction of metal ions occurs only on the

surface of a catalytic substrate in contact with the plating solution. Once the

catalytic substrate is covered by the deposited metal, the plating continues

because the deposited metal is also catalytic.

High corrosion resistance in the as-deposited condition; maintains

better uniform thickness and surface finish; can plate small diameters, deep bores

and intricate shapes.

Disadvantages: Requires high standards of quality control of surface

preparation and plating solution; softer than chrome plating; some metal

limitations.

Fig.2.5. Electroless Nickel plating process

Composite

A composite material is a macroscopic, physical combination of two

or more materials in which one material usually provides reinforcement.

Composites have been developed where no single, quasi-continuous material will

20

provide the required properties. In most composites one phase (material) is

continuous and is termed the matrix, while the second, usually discontinuous

phase, is termed the reinforcement, in some cases filler is applied when the

reinforcement is not a quasi-continuous fibre. Matrix-filler nomenclature is one

method of categorization. This yields the categories metal matrix (MMC),

polymer (plastic) matrix (PMC), and ceramic matrix (CMC) composites — the

major subdivisions of this section. Other categories are given the shape and

configuration of the reinforcing phase. The reinforcement is usually a ceramic

and/or glass. If it is similar in all dimensions, it is a particulate reinforced

composite; if needle-shaped single crystals, it is whisker-reinforced; if cut

continuous filament, chopped fibre-reinforced; and if continuous fibre, fibre

composite. For fibre composites configuration gives a further category. If fibres

are aligned in one direction, it is a uni-axial fibre composite; if arranged in

layers, it is a laminar composite; if a three-dimensional arrangement, it is a 3D

weave composite. Laminates and 3D weaves can be further divided by the weave

used for the fibre.

Ion Implantation

In the Ion plating (IP) process, the target material is initially melted

while the substrate is bombarded with ions before deposition to raise it to the

required temperature. The coating flux ion is attracted to the substrate by biasing

the substrate with a negative voltage. Thus sufficient ion energy is available for

good inter mixing of coating and substrate at the interfaceIon implantation is the

introduction of ionized dopant atoms into a substrate with enough energy to

penetrate beyond the surface. The most common application is substrate doping.

The use of 3 to 500 keV energy for boron, phosphorus or arsenic dopant ions is

sufficient to implant the ions from 100 to 10,000A below the silicon surface. The

depth of implantation, which is proportional to the ion energy, can be selected to

meet a particular application.

21

Implantation offers a clear advantage over chemical deposition

techniques. The major advantage of ion implantation technology is the capability

of precisely controlling the number of implanted dopant atoms. Furthermore, the

dopants depth distribution profile can be well-controlled.

Disadvantages of Ion Implantation are very deep and very shallow

profiles are difficult, not all the damage can be corrected by annealing, typically

has higher impurity content than does diffusion. Often uses extremely toxic gas

sources such as arsine (AsH3), and phosphine (PH3) and expensive

They are generally used in Doping, SIMOX, H and He isolation in

GaAs, and Smart cut technologies.

Fig. 2.6 Schematic diagram of Ion Implantation used in Doping process

Anodizing

Anodizing involves the electrolytic oxidation of a surface to produce a

tightly adherent oxide scale that is thicker than the naturally occurring film.

Anodizing is an electrochemical process during which aluminium is the anode.

22

The electric current passing through an electrolyte converts the metal surface to a

durable aluminium oxide. The difference between plating and anodizing is that

the oxide coating is integral with the metal substrate as opposed to being a

metallic coating deposition. The oxidized surface is hard and abrasion resistant,

and it provides some degree of corrosion resistance.

Anodic coatings can be formed in chromic, sulphuric, phosphoric, or

oxalic acid solutions. Chromic acid anodizing is widely used with 7000 series

alloys to improve corrosion resistance and paint adhesion, and unsealed coatings

provide a good base for structural adhesives. However these coatings are often

discolored and where cosmetic appearance is important, sulphuric acid anodizing

may be preferred.

Fig. 2.7 Anodising electrolytic bath

Boronising

Boronising is also called as boriding. It is a thermo-chemical

treatment involving diffusion of boron into the surface of a component from the

surrounding environment which results in the formation of a distinct compound

23

layer of a metal boride. The reaction takes place between boron and component,

therefore it can be generally limited to steels, titanium-based alloys and cobalt-

based hard metals. In steels, boronising is carried out in the austenite regime

(between 810–1020 °C) for several hours, resulting in the formation of layers

commonly between 60 and 165 m thick. The surface reaction layer thus formed

consists of two separate phases, namely a layer of Fe2B adjacent to the substrate

and an outer layer of FeB. The proportions of the two phases are dependent upon

the composition of the boronising environment and the alloy content of the steel

(higher alloy content favours FeB formation). Care is taken to reduce the

proportion of FeB in the boride layer since this always exists in tension; as such,

high-alloy and stainless steels are unsuitable for boronising. The hardness of the

boronised layer is dependent upon the exact composition of the steel but is

commonly in the range 16000–19000 MPa (as measured on the Vickers scale).

This is significantly higher than many commonly occurring abrasives and, as

such, boronising has been employed in situations requiring abrasive wear

resistance.

A variety of methods are employed to produce the boron-rich

environment for the boronising process such as pack boronising, paste

boronising, salt bath boronising and gas boronising. In pack boronising (the most

commonly employed method), the source of boron is B4C which is mixed with

an activator and an inert diluent to make up the pack powder.

Nitriding

Steels containing nitride-forming elements such as chromium,

molybdenum, aluminium, and vanadium can be treated to produce hard surface

layers, providing improved wear resistance. Many of the processes employed are

proprietary, but typically they involve exposure of cleaned surfaces to anhydrous

ammonia at elevated temperatures. The nitrides formed are not only hard but also

24

more voluminous than the original steel, and therefore they create compressive

residual surface stresses. Therefore, nitrided steels usually exhibit improved

fatigue and corrosion fatigue resistance. Similar beneficial effects can be

achieved by shot peening.

Fig. 2.8 Boronising process Layout

Fig. 2.9 Nitriding process in hardening.

Laser coating technology is increasingly widespread. Surface alloying

is one of many kinds of alteration processes achieved through the use of lasers. It

is similar to surface melting, but it promotes alloying by injecting another

25

material into the melt pool so that the new material alloys into the melt layer.

Laser cladding is one of several surface alloying techniques performed by lasers.

The overall goal is to selectively coat a defined area. In laser cladding, a thin

layer of metal (or powder metal) is bonded with a base metal by a combination of

heat and pressure. Specifically, ceramic or metal powder is fed into a carbon

dioxide laser beam above a surface, melts in the beam, and transfers heat to the

surface. The beam welds the material directly into the surface region, providing a

strong metallurgical bond. Powder feeding is performed by using a carrier gas in

a manner similar to that used for thermal spray systems. Large areas are covered

by moving the substrate under the beam and overlapping disposition tracks.

Shafts and other circular objects are coated by rotating the beam. Depending on

the powder and substrate metallurgy, the microstructure of the surface layer can

be controlled, using the interaction time and laser parameters. Laser surface

treatment can be controlled to achieve alloying, cladding, grain refining or

transformation hardening a metal surface without actually affecting the metal

itself. A material of poor oxidation can be modified with a surface alloy which

can show improved resistance. Laser grain refining eliminates or minimizes

surface defects such as inclusions, pores and improves grain structure.

Carburizing

Carburizing is a heat treatment process in which iron or steel is heated

in the presence of carbon material (in the range of 900 to 950 °C (1,650 to

1,740 °F)). Depending on the amount of time and temperature, the affected area

can vary in carbon content. Longer carburizing times and higher temperatures

lead to greater carbon diffusion into the part as well as increased depth of carbon

diffusion. When the iron or steel is cooled rapidly by quenching, the higher

carbon content on the outer surface becomes hard via the transformation from

austenite to martensite, while the core remains soft and tough as a ferritic and/or

pearlite microstructure.

26

Fig. 2.10. Pack Carburising process

Generally it is used for low-carbon workpiece to increase their

toughness and ductility; and it produces case hardness depths of up to 0.25 inches

(6.4 mm).

Carburization of steel involves a heat treatment of the metallic surface

using a source of carbon. Early carburization used a direct application of

charcoal packed onto the metal (initially referred to as case hardening), but

modern techniques apply carbon-bearing gases or plasmas (such as carbon

dioxide or methane). The process depends primarily upon ambient gas

composition and furnace temperature, which must be carefully controlled, as the

heat may also impact the microstructure of the rest of the material. For

applications where great control over gas composition is desired, carburization

may take place under very low pressures in a vacuum chamber.

Plasma carburization is increasingly used in major industrial regimes

to improve the surface characteristics (such as wear and corrosion resistance,

hardness and load-bearing capacity, in addition to quality-based variables) of

various metals, notably stainless steels. The process is used as it is

environmentally friendly (in comparison to gaseous or solid carburizing). It also

provides an even treatment of components with complex geometry (the plasma

27

can penetrate into holes and tight gaps), making it very flexible in terms of

component treatment.

The process of carburization works via the implantation of carbon

atoms in to the surface layers of a metal. Gas carburizing is normally carried out

at a temperature within the range of 9000 C to 950° C. In oxy-acetylene welding,

a carburizing flame is one with little oxygen, which produces a sooty, lower-

temperature flame. It is often used to anneal metal, making it more malleable and

flexible during the welding process.

A main goal when producing carbonized work pieces is to insure

maximum contact between the workpiece surface and the carbon-rich elements.

In gas and liquid carburizing, the work pieces are often supported in mesh

baskets or suspended by wire. In pack carburizing, the workpiece and carbon are

enclosed in a container to ensure that contact is maintained over as much surface

area as possible. Pack carburizing containers are usually made of carbon steel

coated with aluminium or heat-resisting nickel-chromium alloy and sealed at all

openings with fire clay.

It's possible to carburize only a portion of a part, either by protecting

the rest by a process such as copper plating, or by applying a carburizing medium

to only a section of the part.

The carbon can come from a solid, liquid or gaseous source; if it

comes from a solid source the process is called pack carburizing. Packing low

carbon steel parts with a carbonaceous material and heating for some time

diffuses carbon into the outer layers. A heating period of a few hours might form

a high-carbon layer about one millimetre thick.

28

Liquid carburizing involves placing parts in a bath of a molten carbon-

containing material, often metal cyanide; gas carburizing involves placing the

parts in a furnace maintained with a methane-rich interior.

Cyaniding

Cyaniding is a case hardening process that is fast and efficient; it is

mainly used on low carbon steels. The part is heated to 871-954 °C (1600-

1750 °F) in a bath of sodium cyanide and then is quenched and rinsed, in water

or oil, to remove any residual cyanide.

2NaCN + 2NaCNO 2NaCNO

2NaCNO + O2 NaCO3 +CO + 2N

2CO CO2 + C

This process produces a thin, hard shell (between 0.254 - 0.762 mm [0.010

and 0.030 inches]) that is harder than the one produced by carburizing, and can

be completed in 20 to 30 minutes compared to several hours so the parts have

less opportunity to become distorted. It is typically used on small parts such as

bolts, nuts, screws and small gears. The major drawback of cyaniding is that

cyanide salts are poisonous.

Fig.2.11. Hardening using Cyaniding process.

29

Carbo-nitriding

Carbo-nitriding is similar to cyaniding except a gaseous atmosphere of

ammonia and hydrocarbons is used instead of sodium cyanide. If the part is to be

quenched then the part is heated to 775–885°C (1427–1625 °F); if not then the

part is heated to 649–788°C (1200–1450 °F).

Ferritic Nitro Carburizing

Ferritic nitro-carburizing diffuses mostly nitrogen and some carbon

into the case of a workpiece below the critical temperature, approximately 650°C

(1,202 °F). Under the critical temperature the work piece’s microstructure does

not convert to an austenitic phase, but stays in the ferritic phase, which is why it

is called ferritic nitro-carburization.

Fig.2.12 Carbonitriding Process

Applications

30

Parts that are subject to high pressures and sharp impacts are

commonly case hardened, e.g. firing pins and rifle bolt faces, or engine

camshafts.

Cladding

It is the bonding together of dissimilar metals. It is distinct from

welding or gluing as a method to fasten the metals together. Cladding is often

achieved by extruding two metals through a die as well as pressing or rolling

sheets together under high pressure.

Laser Surface Treatment (LST)

It can be controlled to achieve alloying, cladding, grain refining or

transformation hardening a metal surface without actually affecting the bulk of

the metal itself. LST can be categorized into three main sections and its various

effects on a substrate can be shown as in table 1.1 [Gnanamuthu D.S., 1979].

A laser beam can enhance surface properties to a controlled, confined

extent depending on the power, dwell rime of the beam and the thermal

characteristics, i.e., heating and cooling of the surface treated. Surface treatment

prospects by lasers were observed with pulsed lasers at first. Being inertialess, it

has high processing speeds with very rapid stop and start facility. A material of

poor oxidation or corrosion or wear resistance but low cost can be modified with

a surface alloy which can show improved resistance.

Table 2.1 Effects of application of Laser beam on materials

Heating Melting Shocking

Annealing

Transformation

hardening

Alloying

Cladding

Glazing

Grain Refining

Shock hardening

31

Laser Grain refining eliminates or minimizes surface defects such as

inclusions, pores and improves the grain structure.

Laser Cladding

Laser cladding is a method of depositing material by which a

powdered or wire feedstock material is melted and consolidated by use of a laser

in order to coat part of a substrate or fabricate a near-net shape part (additive

manufacturing technology) .It is used to improve mechanical properties or

increase corrosion resistance, repair worn out parts, and fabricate metal matrix

composites to improve mechanical properties or increase corrosion resistance,

repair worn out parts, and fabricate metal matrix composites.

Fig.2.13. Laser cladding method of depositing material

Other Surface Treatment Processes

Numerous processes are used for surface treatments, based on

mechanical, chemical, thermal and physical. Their principles and characteristics

32

are obtained as follows: Short Peening, Water-Jet Peening and Laser Peening.

In short peening the surface of the work piece is hit repeatedly with

large number of cast-steel, glass or ceramic shot (size of 0.125mm to 5mm

diameter), making overlapping indentation on the surface; this action causes

plastic deformation of the surfaces. Thus improving the fatigue life of the

component. Extensively used on shafts, gears, springs, oil-well drilling

equipment, and jet engine parts.

In water-jet peening, a water jet at pressure as high as 400 MPa

impinges on the surface of the work piece, inducing compressive residual

stresses. This have been successfully used on steels and aluminum alloys.

In laser peening, the surface is subjected to laser shocks from high

powered laser up to 1KW and at energy levels of 100 J/pulse. This method has

been used on jet engine fan blades with compressive residual stresses deeper than

1mm.

Roller Burnishing (Surface Rolling)

The surface of the component is cold worked by hard and highly

polished roller or rollers; this process is used on various flat, cylindrical or

conical surfaces. Roller burnishing improves surface finish by removing

scratches, tool marks and pits.

Explosive Hardening

The surface is subjected to high transient pressures by placing a layer

of explosive sheet directly on the work piece surface and detonating it. Large

increase in surface hardness can be obtained by this method. Railroad rail

surfaces can be hardened by this method.

33

Mechanical Plating

Fine particles of metal are compacted over the work piece surfaces by

impacting them with spherical glass, ceramic, or porcelain beads. The beads are

propelled by rotary means. This process typically is used for hardened-steel parts

for automobiles.

Case Hardening

The formation of martensite in case hardening of steels causes

residual stresses on surfaces. Such stresses are desirable, because they improve

the fatigue life of components by delaying the initiation of fatigue cracks.

Hard Facing

A relatively thick layer, edge or point of wear-resistant hard metal is

deposited on the surface by any of the welding techniques. Hard coatings of

tungsten carbide, chromium and molybdenum carbide are also deposited by this

method. Typical applications for hard facing include valve seats, oil-well drilling

tools and dies for hot metal working.

Surface Texturing

Manufactured surfaces can be further modified by secondary

operations for technical, functional, optical or aesthetic reasons. These additional

processes generally consist of etching, electric arcs, laser pulses, atomic oxygen

with reacts with surfaces and produces fine, cone like surface textures.

Diffusion Coating

In this process, an alloying element is diffused into the surface of the

substrate, thus altering its properties. Such elements can be supplied in solid,

liquid or gaseous state. This process is given different names, depending on the

34

diffused element, that describe diffusion process, such as carburizing, nitriding,

and boronizing.

Electroplating

The work-piece (cathode) is plated with a different metal (anode)

while both are suspended in a bath containing a water-base electrolyte solution.

The metal ions from the anode are discharged under the potential from the

external source of electricity, combine with the ions in the solution, and are

deposited on the cathode. All metals can be electroplated, with thickness ranging

from a few atomic layers to a maximum of about 0,05mm.Typical application

include copper plating aluminum wire and phenolic boards for printed circuits,

chrome plating hardware, tin plating copper electrical terminals for ease of

soldering and plating various components for good appearance and resistance to

wear and corrosion.

Electroforming

A variation of electroplating, electroforming is actually a metal-

fabrication process. Metal is electrodeposited on a mandrel, which is then

removed; thus, the coating itself becomes the product. Simple and complex

shapes can be produced by electroforming, with wall thickness as small as

0.025mm.

Conversion Coating

In this process, also called chemical-reaction priming, a coating forms

on metal surfaces as a result of chemical or electro chemical reactions. Various

metals, particularly steel, aluminum, and zinc, can be conversion coated. Oxides

that naturally form on their surfaces are a form of conversion coating;

phosphates, chromates, and oxalates are used to produce conversion coatings.

35

These coatings are used for purposes such as pre-painting, decorative finishes,

and protection against corrosion.

Hot Dipping

In this process, the work piece, usually steel or iron, is dipped into a

bath of molten metal, such as zinc, tin, aluminum and terne (lead alloyed with

10% to 20% tin). Hot dipped coatings on discrete or sheet metal provide

galvanized pipe, plumbing supplies, and many other products with long time

resistance to corrosion. Various pre-coated steel sheets are used extensively in

automobile bodies.

Porcelain Enameling

Metals may be coated with a variety of glassy coatings to provide

corrosion and electrical resistance and for service at elevated temperatures. These

coatings are usually classified as porcelain enamels and generally include

enamels and ceramics. Enameling involves fusing the coating material on the

substrate by heating them both to 425°C to 1000°C to liquefy the oxides. Typical

application include household appliances, plumbing fixtures, chemical

processing equipment, signs, cook ware and jewelry; they are also used as

protective coatings on jet-engine components.

Organic Coatings

Metal surfaces maybe coated or pre-coated with a variety organic

coatings, films and laminates to improve appearance and corrosion resistance.

Coatings are applied to the coil stock on continuous lines, with thickness

generally of 0.0025mm to 0.2mm. Such coatings have a wide range of properties:

flexibility, durability, hardness, resistance to abrasion and chemicals, color,

texture and gloss. Application of organic coatings are coatings for naval aircraft

that subjected to high humidity, rain, sea water, pollutants, aviation fluids,

36

Deicing fluids and battery acids that are also impacted by particles such as dust,

gravel, stones and deicing salts.

Painting

Because of its decorative and functional properties, paint is widely

used as a surface coating. Paints are basically classified as enamels, lacquers and

water base paints, with a wide range of characteristics and applications. They are

applied by brushing, dipping, spraying, or electro statically.

Diamond Coating

Important advances have been made in diamond coating of metals,

glass, ceramics and plastics, using various chemical and plasma assisted vapor

deposition process and ion beam enhanced deposition techniques. Development

of these techniques, combined with important properties of diamonds, such as

hardness, wear resistance, high thermal conductivity and transparency to ultra

violet light and microwave frequencies has enabled the production of various

aerospace and electronic parts and components.

Diamond Like Carbon (DLC)

By using a low temperature, ion beam assisted deposition process, this

relatively recently developed materials is applied as a coating of a few

nanometers in thickness. Less expensive than diamond films, but with cylinder

properties as diamond, DLC has applications in such areas as tools and dies,

gears, bearing, micro electro-mechanical systems, and micro scale probes.