MF9111 - ADVANCE MATERIALS TECHNOLOGY

ASSIGNMENT

SELECTION OF MATERIALS FOR CUTTING TOOLS

CBN & PCD

PREPARED BY,

KARTHICK.N

2009606001

M.E. MANUFACTURING ENGG

ANNA UNIV – MIT, CHROMPET.

CONTENTS

1. CUBIC BORON NITRIDE 1.1. INTRODUCTION

1.2. ORIGIN

1.3. GENERAL DETAILS

1.4. PROPERTIES

1.4.1. CRYSTALLOGRAPHIC PROPERTIES

1.4.2. MECHANICAL PROPERTIES

1.4.3. THERMAL PROPERTIES

1.4.4. THERMODYNAMIC PROPERTIES

1.4.5. ELECTRIC PROPERTIES

1.4.6. CHEMICAL REACTIVITY

A. WITH METALS

B. WITH OXIDES

C. WITH ACIDS AND BASES

D. WITH BIOLOGICAL SYSTEMS

1.5. APPLICATIONS

1.5.1. CUTTING TOOL APPLICATIONS

1.5.2. OTHER APPLICATIONS

1.6. CBN TYPICAL MACHINING PARAMETERS

1.7. ADVANTAGES

1.8. DIFFERENT OPERATIONS USING CBN

1.9. POSSIBLE CRYSTAL STRUCTURES OF CBN

1.10. STRUCTURE OF A CBN WHEEL OF AN ESTABLISHED COMPOSITION

1.11. RELATIVE STRENGTH OF THREE REPRESENTATIVE CBN GRADES

AFTER HEAT TREATMENT AT DIFFERENT TEMPERATURES

1.12. SPLINTER SIZE OF THREE REPRESENTATIVE CBN GRADES

AFTER HEAT TREATMENT AT DIFFERENT TEMPERATURES

1.13. DIFFERENT GRADES OF CBN

1.14. COMPARISONS OF SOME CBN PRODUCTS AVAILABLE IN MARKET

2. POLY-CRYSTALLINE DIAMONDS

2.1. INTRODUCTION

2.2. NATURAL PCD

2.2.1. PROPERTIES

2.3. ARTIFICIAL PCD

2.3.1. FABRICATION

2.3.2. PROPERTIES

2.4. APPLICATIONS

2.5. MANUFACTURING DIFFERENT SHAPES OF PCD

2.6. DIFFERENT SIZES OF PCD IN USED VARIOUS APPLICATIONS

2.7. PHYSICAL PROPERTIES OF SOME PCD PRODUCTS

2.8. ADVANTAGES

2.9. DISADVANTAGES

3. REFERENCES

1. CUBIC BORON NITRIDE 1.1. INTRODUCTION:

The second hardest material, Cubic Boron Nitride (CBN), is created by man, using temperatures and pressures similar to those for diamond synthesis. Used in the correct manner CBN offers cost-effective rapid stock removal and finishing of hardened steels and certain softer ferrous materials. The lattice structure is hexagonal similar to that of graphite.

Engineers throughout the world are improving productivity and quality, and reducing grinding cost per piece, by replacing Al2O3 wheels with CBN (cubic boron nitride) wheels made with porous vitrified bonds.

1.2. ORIGIN:

The cubic form was only realised after the discovery, in 1957, by R. H.

Wentorf Jr. of the General Electric Company, USA, that the hexagonal form

could be transformed to the cubic by the use of high temperatures and

pressures.

1.3. GENERAL DETAILS:

TABLE - 1

Formula BN

Essentially stoichiometric but, Small amounts (generally < 1%) of impurities C, O, Li, Be, S,P &

others may be present depending on chemistry of

growth system.

Molecular Weight 24.8177 43.6 wt% B; 56.4 wt% N

Name

Cubic boron nitride Cubic BN;

CBN; BORAZON

β-BN Elbor

Cubonite

General Electric Co. trademark for abrasive Grain.

Russian scientific literature Russian abrasive Russian abrasive

1.4. PROPERTIES:

Properties of all the materials arise from their structure, i.e., from the

manner in which their atoms aggregate into hierarchies. Let us see the various

properties of cubic boron nitride here.

1.4.1. CRYSTALLOGRAPHIC PROPERTIES:

Crystal morphology is a determining factor for the physical, thermal

and chemical properties of the CBN grit. TABLE - 2

Colour

Colourless (rare);

Generally, yellow (amber, honey, cinnamon), orange,

black (B-doped),

brown, deep blue (Be-doped).

Yellow and orange crystals are thermo chromic and become opaque about 450 °C.

Crystal system Cubic

Structure type Zinc blende

Atoms/unit cell 4B, 4N

Lattice constant (25 °C) [nm] 0.3615 ± 0.0001

Ionic distance (B-N) [nm] 0.157

Density [g/cm3] 3.48 calculated from X-ray data

3.45 measured data

Crystal habit

truncated tetrahedra or octahedra {111} hexagonal plates {111}

{111} and {100} {111} and {110}

crystals twinned on {111} irregular blocky forms

Twinning growth twinning on {111}

Cleavage perfect on {011}

1.4.2. MECHANICAL PROPERTIES:

Mechanical properties determine the strength related factors of the

materials.

TABLE - 3

Hardness [HK]

4366,

4695 (undoped);

4572 (Be-doped)

4500 on {111} in <110>

~ 4500

Elastic constants [Pa]

C11 = 7.12 · 1011 calculated from C11/Co

C12 = 0.8 · 1011 estimated

C44 = 3.34 · 1011 calculated from C44/Co

Bulk modulus K = (C11 +2C12)/3 ≈ 2.9X1011

Compressibility [cm2 10 µN−1]

0.24 - 0.37 · 10−12 calculated range from various relationships

0.34 · 10−12 calculated from elastic constants (1/K)

Temperature for dislocation mobility [°C] > 1300

Fracture mode Cleaves easily on the 6 {011} planes Some crystals crack on heating to about 900 °C

Note: 1.The accepted hardness value is 4500 HK (about half that of diamond).

Surface microstructure (as grown)

triangular and hexagonal steps triangular etch pits

twin planes

Internal microstructure

Alternating color zones probably due to differential impurity adsorption during growth.

Zones revealed by contrast in secondary electron scattering in scanning electron

microscope; also by polishing.

1.4.3. THERMAL PROPERTIES: Cubic boron nitride is extremely stable in air, nitrogen or vacuum -

temperatures ca. 1400 - 1550 °C have to be exceeded before any change in stability occurs. This is in marked contrast to diamond which starts to form a graphite surface film at temperatures ca. 650 °C in the presence of oxygen.

The specific heat values are approximately twice that for diamond, whilst the thermal conductivity value is much lower than that of diamond. The values for thermal expansion between 430 °C and 1160 °C are slightly higher than those for diamond.

TABLE - 4

Specific heat

[J/(mol K)]

12.55 at 300 K

25.1 at 600 K

Debye temperature

[K]

1700 from IR spectra

1900 from extrapolated elastic constants

Thermal conductivity

[W/(m K)] (25 °C)

200 measured on dense polycrystalline compacts 1300 calculated 87.5 by extrapolation of data from porous compacts

Linear thermal

expansion

[10−6/K]

4.80 at 430 °C

4.30 at 700 °C

5.60 at 900 °C

5.80 at 1160 °C

Thermal stability

at < 1 atm

at high pressure

Air, oxygen: B2O3 protective layer prevents further oxidation to ~ 1300 °C; no conversion to hexagonal form at 1400 °C.

Nitrogen: some conversion to hex at 1525 °C in 12 h, vac.

Vacuum (10−5 Pa): threshold temperature for conversion to hex, 1550 - 1600 °C.

3125 - 3225 °C, threshold conversion temperature for flash heating at 5 - 9 GPa.

1.4.4. THERMODYNAMIC PROPERTIES:

TABLE - 5

Melting point at triple point[K] ~ 3500 at 10.5 GPa

Heat of formation [kJ mole−1]

−251 value for the graphitic layer lattice form at 298 K −266 calculated value for CBN

Entropy S [J mol−1 K−1]

0.58 calculated at 298 K

Cubic - hex

transformation

p = (0.0037 T [K] −1.8 ) [GPa], applicable from ~ 4.5 to

7.5 GPa with solvent catalyst such as Li3BN2

Lattice energy, U [kJ mol−1]

22608 14319

Cohesive energy, ∆Gs [kJ mol−1]

1214 spectroscopic analysis

1315 calculated

Surface energy [J cm−2]

σ111 (free specific surface energy) 4720 x 10−7 (calculation)

1.4.5. ELECTRIC PROPERTIES:

One of the important characteristics of the materials is their ability to permit or resist the flow of electricity. RESISTIVITY[Ω Cm]: p-type (Be-doped) 102– 104 0.19 - 0.23 eV (activation energy for conduction) n-type (B, S, Si, CN-doped) 103 - 107 0.05 - 0.41 eV (activation energy for conduction) 1010 undoped; resistance of undoped yellow crystals decreases from ~1010 to ~ 107 from 25 °C to 500 °C (colour change accompanies resistance decrease).

DIELECTRIC CONSTANT: ε0= 7.1 ε∞ = 4.5

1.4.6. CHEMICAL REACTIVITY: Study of chemical properties of materials is necessary because most of

the engineering materials, when they come in contact with other substances

with which they can react, tend to suffer from deterioration.

Let us see the chemical reactivity of CBN with various substances.

TABLE - 6

A. WITH METALS: B. WITH OXIDES:

Mo - in 10−2 Pa vacuum - reaction with CBN - 1360 °C

Ni - in 10−2 Pa vacuum - wets CBN at 1360 °C

Fe, Ni, Co - Ar, reaction with CBN begins -1350 - 1400 °C

Fe, Ni, Co - in 10−3 Pa vacuum - wetting of hex BN

Fe and/or Ni-based alloys containing Al - reaction with CBN 1250 - 1300 °C

Al in 10−3 Pa vaccum, 1050 °C - marked wetting and reaction with CBN and hex BN

Si in 10−3 Pa vacuum, 1500 °C - wetting of CBN

Fe, Co, Ni, Si in 10−3 Pa vacuum, 1550 °C - wet hex BN work of wetting - 1000 - 3500 erg/cm2

Cu, Ag, Au, Ga, In, Ge, Sn - 10−3 Pa vacuum, 1100 °C - no

wetting of CBN or hex BN

work of wetting = 60 - 350 erg/cm2 B - does not wet hex BN even at 2200 °C; addition of 0.1

- 1% Ti or Cr increases wetting

ZnO-PbO-B2O3-SiO2 - glasses used as binder for Cubonite tool – wetting Indicated

1.5. APPLICATIONS:

1.5.1. CUTTING TOOL APPLICATIONS:

Typically they are used for hard ferrous materials (Rc 45 or harder) that are difficult to machine with carbide or ceramic or that require time consuming grinding operations.

• Automotive engine blocks - Cylinder Boring

• Brake rotors - O.D. Facing and Chamfer

• Transmission gears - I.D. Boring

• Steel mill rolls - O.D. Turning

• Cylinder head - Milling

C. WITH ACIDS AND BASES: D. WITH BIOLOGICAL SYSTEMS:

Na2O-CaO-B2O3-SiO2 - argon 800 °C, cubic BN wetted by liquids in this system.

ZrO2 , V2O5 and TiO2 and K2O additions decrease wetting

Li-Al silicate plus fireclay fired at 905° - 1000 °C to bind CBN grains in grinding wheel - suggests wetting by

molten silicate.

Li2O - B2O3 liquid wets CBN at 5 GPa and 1400 - 1700 °C

insoluble in usual acids

soluble in alkaline molten salts, LiOH, KOH, NaOH-Na2CO3, NaNO3.

These are used for etchants. Soluble in molten nitrides such as Li3N, Mg3N2, Sr3N2,

Ba3N2, Li3BN2.

BN (along with Si3N4, NbN, and BNC) are reported to show weak fibri-genic activity & cause pneumoconiosis. Maximum concentration recommended for nitrides of

nonmetals is 10 mg/m3; for AlN, 4; for ZrN, 4.

1.5.2. OTHER APPLICATIONS:

High temperature lubricants Mold release agents Insulating filler material in composites Filler for silicone rubber Additive in silicone oils and resins Filler for tubular heaters and neutron absorbers

1.6. CBN TYPICAL MACHINING PARAMETERS :

TABLE - 7

Material Speed (sfpm)

Feet Rate (inch/rev)

D.O.C. (inches)

Gray Cast Iron (180-270 BHN) 2000-4000 .005-.025 .005-.100

Hard Cast Iron (>400 BHN) 250-500 .005-.025 .005-.100

Hardened Steel (>45 Rc Roughing)

225-350 .005-.020 .030-.100

Hard Facing Alloys 300-700 .005-.010 .005-.050

Powder Metal 300-600 .004-.010 .004-.040

Superalloys 500-1000 .004-.010 .004-.040

Thermal Spray - N. Based 300-1000 .003-.008 .004-.040

Thermal Spray - C. Based 400-1000 .002-.006 .004-.040

1.7. ADVANTAGES:

ROUGHING : • Efficient machining of pearlitic gray cast iron • Turning hard facing alloys • Machining of powder metal alloys • Turning of superalloys

FINISHING : • High speed finish machining of hardened steel (>45 Rc) • Suitable for continuous machining of hardened steels • Replace grinding operations.

1.8. DIFFERENT OPERATIONS USING CBN:

Turning with CBN Machining Case Hardened Steel Gear

Rough and semi-finish turning, milling,

Grooving and boring Machining White Iron Roll with CBN

Through Hardened EN31

Bearing Steel Machining Boring Nitrided Aero Engine Bearing Cage

1.9. POSSIBLE CRYSTAL STRUCTURES OF CBN:

FIGURE - 1

1.10. STRUCTURE OF A CBN WHEEL OF AN ESTABLISHED COMPOSITION:

FIGURE - 2

1.11. RELATIVE STRENGTH OF THREE REPRESENTATIVE CBN GRADES AFTER HEAT TREATMENT AT DIFFERENT TEMPERATURES:

FIGURE - 3

1.12. SPLINTER SIZE OF THREE REPRESENTATIVE CBN GRADES AFTER HEAT TREATMENT AT DIFFERENT TEMPERATURES: FIGURE - 4

1.13. DIFFERENT GRADES OF CBN:

H.C. Starck Grade A 01 Boron Nitride, BN

H.C. Starck Grade B 50 Boron Nitride, BN

H.C. Starck Grade B 100 Boron Nitride, BN

H.C. Starck Grade C Boron Nitride, BN

H.C. Starck Grade F 15 Boron Nitride, BN

1.14. COMPARISONS OF SOME CBN PRODUCTS AVAILABLE IN MARKET:

(NOTE: a )Trade names and trademarks of De Beers Industrial Diamond Division, S. Africa.)

Following table illustrates some of the important properties of Amborite - AMB90 , DBC 50 and DBA80 and compares them with those of an aluminum oxide ceramic cutting tool material.

TABLE - 8

Property Amboritea) Amboritea)

DBC50 Amboritea)

DBA80 Al2O3+ TiC

AMB90

Density [g/cm3] 3.42 4.28 3.52 4.28

Compressive strength [GPa]

2.73 3.552 - 4.5

Fracture toughness [MPa m1/2]

6.4 3.7 5.9 2.94

Knoop hardness [HK]

31.5 27.5 30 17

Young’s modulus [GPa]

680 587 649 390

Thermal expansion

[10−6/K] 4.9 4.7 4.6 7.8

Thermal conductivity

[W/(m K)] 100 44 85 9

Wear Coefficient

1.9 1.34 1.76 0.92

2. POLY-CRYSTALLINE DIAMONDS

2.1. INTRODUCTION:

Diamond is the hardest, most abrasive-resistant, material known to man. These properties make diamond an ideal cutting tool. Within the crystal structure, however, fracture planes, used by the diamond cutter to produce the gem diamond from the rough, can cause catastrophic breakage of the tool edge, when subjected to impact.

PCD tools incorporate Polycrystalline Diamond blanks produced under conditions of high pressure (1 million PSI) and temperature (1700 Degrees C), similar to those of diamond synthesis. Randomly orientated, carefully selected synthetic diamond crystals are grown together on a hard metal substrate.

This results in a material with the hardness, abrasive resistance and high thermal conductivity of diamond with the toughness of hard metal. Using the hard metal substrate the PCD blank is brazed to a carrier, either steel or hard metal, and machined by grinding or E.D.M to produce the cutting edge.

When compared to other cutting tool materials, there are three main reasons for using PCD tools:-

Increased tool life results in reduced tool cost per component and less idle machine time.

Increasing cutting speed improves productivity through reduced cycle times.

Grinding and other less productive machining methods can be replaced by PCD milling and turning.

PCD (Polycrystalline Diamond) has been available for milling non-ferrous abrasive materials for many years. The common method of tool production has been grinding using Diamond grinding wheels.

The forces required to grind PCD with Diamond are extremely high. This means that it has been very difficult to produce cutting tool inserts accurately enough to work properly in the fixed pocket milling cutters commonly available. Cutters with adjustable pockets for the inserts were developed, but these require care and patience to set up and are expensive to buy and repair.

Poly – Crystalline Diamonds exist both in nature and also can be manufactured artificially using man-made diamond particles.

2.2. NATURAL PCD:

Carbonado, commonly known as the "Black Diamond", is a natural polycrystalline diamond found in alluvial deposits in the Central African Republic and Brazil. Its natural colour is black or dark grey, and it is more porous than other diamonds.

TABLE - 9

CHEMICAL FORMULA C

MOLAR MASS 12.01 U

COLOR TYPICALLY BLACK

CRYSTAL HABIT POLYCRYSTALLINE

CRYSTAL SYSTEM ISOMETRIC-HEXOCTAHEDRAL (CUBIC)

FRACTURE CONCHOIDAL (SHELL-LIKE)

MOHS SCALE HARDNESS 10

STREAK WHITE

SPECIFIC GRAVITY 3.52±0.01

DENSITY 3.5–3.53 G/CM3

POLISH LUSTER ADAMANTINE

The most characteristic carbonados have been found only in the Central African Republic and in Brazil, in neither place associated with kimberlite, the source of typical gem diamonds.

Lead isotope analyses have been interpreted as documenting crystallization of carbonados about 3 billion years ago. The carbonados are found in younger sedimentary rocks.

2.2.1. PROPERTIES:

1. Carbonado diamonds are typically pea-sized or larger porous aggregates of many tiny black crystals.

2. Carbonado exhibits strong luminescence (photoluminescence and cathodoluminescence) induced by nitrogen and by vacancies existing in the crystal lattice.

3. Isotope studies have yielded further clues to carbonado genesis. The carbon isotope value is very low (little carbon-13 compared to carbon-12, relative to typical diamonds).

Mineral grains included within diamonds have been studied extensively for clues to diamond origin:

1. Some typical diamonds contain inclusions of common mantle minerals such as pyrope and forsterite, but such mantle minerals have not been observed in carbonado.

2. In contrast, some carbonados do contain inclusions of minerals characteristic of the Earth’s crust: these inclusions do not necessarily establish formation of the diamonds in the crust, however, because these obvious crustal inclusions occur in the pores that are common in carbonados. These inclusions within pores may have been introduced after carbonado formation. Inclusions of other minerals, rare or nearly absent in the Earth’s crust, are found at least partly incorporated in diamond, not just in pores: among such other minerals are those with compositions of Si, SiC, and Fe-Ni. No distinctive high-pressure minerals, including the hexagonal carbon polymorph, lonsdaleite, have been found as inclusions in carbonados, although such inclusions might be expected if carbonados formed by meteorite impact.

2.3. ARTIFICIAL PCD:

In 1976, the Baker Hughes Inc. company introduced bits with synthetic

diamond cutters called polycrystalline diamond compact (PDC) bits.

2.3.1. FABRICATION:

It is manufactured using man-made diamond particles that are grown together in a high pressure, high temperature process. At the same time, these particles are integrally bonded to a cemented tungsten carbide substrate for mechanical strength and impact resistance.

2.3.2. PROPERTIES:

Poly-crystalline diamond bits (PCD) offer hardness, strength and abrasion resistance of natural diamond without its susceptibility to fracturing.

TABLE - 10

Properties Metric UNITS Comments

Vickers Micro hardness

25.0 - 98.0 GPa

Modulus of Elasticity

749 - 953 GPa

Compressive Strength

1900 - 6900 MPa values depend on grain size and Co

content

Poisson’s Ratio

0.0700 - 0.200

Fracture Toughness

6.00 - 8.80 MPa-m½ values depend on grain size and Co

content

Density 3.00 - 4.00 g/cc

Thermal Conductivity

1200 W/m-K Thick film diamond made by SP3. 1800 W/m-K De Beers thermal thick film synthetic diamond.

Descriptive Properties

Colour Clear Impurities (i.e. Nitrogen) and irradiation can change color to yellow, green, blue,

pink, or brown. Crystal

Structure Cubic Diamond - Space Group Fd3m

2.4. APPLICATIONS:

1. It can be inserted into PCD cutting tools, PCD drilling bits/core bits,

PCD wire drawing dies, reamers and other wear resistant components.

2. Poly-crystalline diamond bits are well suited to high speed cutting of aluminium, particularly when good surface finishes are mandatory.

3. Often, poly-crystalline diamond bits are recommended for cutting high content silicon aluminium alloys.

4. These diamond bits are also used on brass, copper, carbide and bronze in applications including turning, boring, profiling, grooving, milling and hole making.

5. Used for oil field drilling and coal mining.

2.5. MANUFACTURING DIFFERENT SHAPES OF PCD:

TSP can be manufactured into a variety of sizes and shapes (Cubes,

cylinders, Discs, Rectangles, Triangles, spheres , etc.,).

TSP/PCD mining and oil drilling bits are best suited for more abrasive or

broken formations. PCD drill bits are suitable for drilling in soft rocks with

hardness below 7 degrees such as lime rock, marble, shale, etc., and in

medium to hard rocks with coarse grains such as sedimentary rock.

FIGURE - 5

2.6. DIFFERENT SIZES OF PCD IN USED VARIOUS APPLICATIONS:

TABLE - 11

2.7. PHYSICAL PROPERTIES OF SOME PCD PRODUCTS:

(NOTE: a )Trade names and trademarks of De Beers Industrial Diamond Division, S. Africa.)

Following table illustrates some of the important properties of Syndite a) CTB 010, Syndrill a) SRC, Syndax a) 3 and compares with the mono crystalline diamond.

TABLE - 11

Property Syndite a) CTB 010

Syndrill a) SRC

Syndax a) 3

Mono-crystalline diamond

Hardmetal

WC-6 Co

Density [g/cm3] 4.12 3.99 3.42 3.52 14.7

Compressive strength [GPa] 7.60 7.61 4.192 8.68 4.438

Fracture toughness [MPa m1/2]

8.81 9.80 6.89 3.46 10.48

Knoop hardness [HK] 50 50 50 57 - 104 17

Young’s modulus *GPa+ 776 810 925 1141 593

Thermal expansion [10−6 K−1]

4.2 4.6 3.8 1.5 - 4.8 5.4

Thermal conductivity [W/(m K)] 540 760 120 500 - 2000 100

Wear coefficient 3.89 3.97 2.99 2.14 - 5.49 1.15

2.8. ADVANTAGES:

Poly-crystalline diamond bits offer a number of advantages to manufacturing operations in terms of application range and productivity.

1. The results obtained in drilling medium to hard rocks and non – uniform abrasive formations are much better than those obtained with drill bits impregnated or surface-set with single natural diamond crystals.

2. A factor that improves the toughness of poly-crystalline diamond is the presence of cobalt in the microstructure along with the random orientation of the diamond particles. The tungsten carbide substrate also provides mechanical support for the diamond abrasive layer, increasing impact resistance and making it easier for braze attachment in tool fabrication.

3. Another benefit of poly-crystalline diamond bits is the range of diamond grades available to fit any nonferrous application.

Typically, fine-grain diamond is used for less abrasive applications requiring an excellent surface finish. Medium-grain diamond is considered a general-purpose machining grade. Coarse-grain diamond is used in rough machining and in extremely abrasive materials where surface finish may not be as important.

4. It also excels in machining highly abrasive work pieces.

2.9. DISADVANTAGES:

Because of a chemical interaction between diamond and iron, poly-crystalline diamond bits are not typically used to cut ferrous materials. However, diamond bits can be used to tackle bimetal applications involving aluminium and cast iron.

3. REFERENCES

1. http://www.springerlink.com/content/x584423376016731/fulltext.pdf

2. http://www.cutting-

tool.americanmachinist.com/guiEdits/Content/bdeee15/bdeee15_1.aspx

3. http://www.meister-abrasives.ch/en/technology/abrasive_materials/cbn

4. http://www.china-superabrasives.com/Cubic_Boron_Nitride.htm

5. http://www.wwsuperabrasives.com/Cubic_Boron_Nitride.html

6. http://china-superabrasives.com/PCD_polycrystalline_diamond.htm

7. http://www.xinruitools.com/sl_001.html

8.http://pubs.acs.org/action/doSearch?action=search&searchText=cubic+boro

n+nitride&qsSearchArea=searchText&type=within&publication=40026050

9. http://drengus.com/featured/what-is-pcd/