chapter 7 - engineering ceramics

8122019 Chapter 7 - Engineering Ceramics

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Engineering Ceramics

Definition

Ceramics are inorganic non-metallicmaterials processed or consolidated at hightemperatures

2



Revision 1 April 20113

Microstructural Features Of A

Crystalline Ceramic

Grains (crystals) of the ceramic

Grain boundaries where 2

crystals meet

Pores left by processing

(1 to 1000 micro micromicro micro m)

Microcracks caused

by thermal or

mechanical stress

Particles or grains of asecond phase (in alloys)


General Properties Of Ceramics

bull High hardness

- This is largely due to the operation of the strong covalent

bonds between atoms in their crystal structures

bull Low ductility

bull Low tensile strength

- Due to the presence of micro-cracks

bull High compressive strength

bull High brittleness

bull High abrasion resistance




General Properties Of Ceramics ndash contrsquo

bull Extremely stiff and rigid

bull High melting or degradation temperature

bull Low coefficient of expansion

bull Low electrical conductivity

bull High resistance to oxidationbull High chemical (corrosion) resistance


General Properties Of Ceramics ndash contrsquod

bull Low densityhigh specific compressivestrength even at elevated temperature

(600oC ndash 1600oC) with little creep

For other temperatures the following materialsare more cost-effective

22oC ndash 300oC (Polymers)

22oC ndash 600oC (Metals alloys)




Comparison Of The Hardness Of

Ceramics To Other Materials


Comparison Of Metals With Ceramic Materials

Metals Ceramics

Crystal structure Crystal structure

Metallic bond Ioniccovalent bond

Good electrical

conductivity

Poor conductivity

Opaque Transparent (in thin

sections)

Uniform atoms Different-sized atoms

High tensile strength Poor tensile strength

Low shear strength High shear strength




Comparison Of Metals With CeramicMaterials ndash contrsquod

Metals Ceramics

Good ductility Poor ductility (brittle)

Plastic flow None

Impact strength Poor impact strength

Non porous Initial high porosity

Relatively high weight Lower weight

Moderate hardness Extreme hardness

High density Initial low density


Applications Of

Common Ceramics




Cross section of

assembledautomotive spark

plug showing

position ofceramic insulator

(in red)


Typical Machine Applications Of Ceramics

Cemented Carbide

Knives

Alumina Wear Tiles




Typical Machine Applications OfCeramics ndash contrsquod

Boron Carbide

Abrasive BlastingNozzle

Chromia Wire Guide



Cemented Carbide Die Alumina WebGuide





Alumina Shaft Sleeve Cemented CarbideTool Insert



Chromium Oxide Slurry Pump Liner






Properties Of Ceramics ndash contrsquod

bull Cermets have good ductility and toughnessat high temperatures but lack strength and

creep resistance Metal content is high (65 to75)


Applications Of Cermets

Particle

Material

Bond Structural

Type

Characteristicamp Use

Flake sliver orcopper

Graphite Laminated Current brushes 991251low friction

Alumina (70) Chromium (30) Bonded particles Very suitable for

high temperatureservice Goodresistance toimpact

Magnesia Nickel Flame sprayedheat resistant

coating

Applicable tostainless steel

alloy steel andinconel to raisethe workingtemperature byabout 80oC




Applications Of Cermets ndash contrsquod

Particle Material Bond Structural Type Characteristic amp

Use

Alumina

(40 - 70)

Iron (30 991251 60) Bonded particles Turbine blades

Molybdenum boride Nickel Bonded particles Cutting tool for

machining titanium

Titanium carbide Various alloyscontaining Mo Aland Cr

Bonded particles In aircraft engineswhere refractorinessthermal shock-

resistance andresistance to

oxidation isnecessary

Tungsten or titanium

carbide

Cobalt Bonded particles Cutting tools for

materials including

masonry glass andmetal forming dies


Properties And Applications OfIndustrial Diamonds

Properties

Diamond is the hardest ceramic material (Knoop = 7000)

Modulus of elasticity is also the highest of theceramic materials (E = 1000 GNm2) and it isabout 5 times that of most steels

Tensile strength of diamond is about 69

GNm2

The melting temperature is 4350oC and is thehighest of all the materials




Properties And Applications Of IndustrialDiamonds ndash contrsquod

bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters

Diamond grinding wheel

Diamond polishing

Lapping process

Revision 1 April 2011 24 24



Revision 1 April 20113

Microstructural Features Of A

Crystalline Ceramic

Grains (crystals) of the ceramic

Grain boundaries where 2

crystals meet

Pores left by processing

(1 to 1000 micro micromicro micro m)

Microcracks caused

by thermal or

mechanical stress

Particles or grains of asecond phase (in alloys)


General Properties Of Ceramics

bull High hardness

- This is largely due to the operation of the strong covalent

bonds between atoms in their crystal structures

bull Low ductility

bull Low tensile strength

- Due to the presence of micro-cracks

bull High compressive strength

bull High brittleness

bull High abrasion resistance
























Metals Ceramics



Good electrical

conductivity

Poor conductivity


sections)








Metals Ceramics


Plastic flow None







Applications Of

Common Ceramics




Cross section of


plug showing


(in red)



Cemented Carbide

Knives

Alumina Wear Tiles





Boron Carbide


Chromia Wire Guide






















Particle

Material

Bond Structural

Type







coating








Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process

























Metals Ceramics



Good electrical

conductivity

Poor conductivity


sections)








Metals Ceramics


Plastic flow None







Applications Of

Common Ceramics




Cross section of


plug showing


(in red)



Cemented Carbide

Knives

Alumina Wear Tiles





Boron Carbide


Chromia Wire Guide






















Particle

Material

Bond Structural

Type







coating








Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process






Metals Ceramics


Plastic flow None







Applications Of

Common Ceramics




Cross section of


plug showing


(in red)



Cemented Carbide

Knives

Alumina Wear Tiles





Boron Carbide


Chromia Wire Guide






















Particle

Material

Bond Structural

Type







coating








Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process





Cross section of


plug showing


(in red)



Cemented Carbide

Knives

Alumina Wear Tiles





Boron Carbide


Chromia Wire Guide






















Particle

Material

Bond Structural

Type







coating








Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process






Boron Carbide


Chromia Wire Guide






















Particle

Material

Bond Structural

Type







coating








Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process




















Particle

Material

Bond Structural

Type







coating








Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process







Use

Alumina

(40 - 70)



machining titanium






carbide


materials including




Properties




GNm2






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process






bull Applications

- Cutting

- Grinding

- Polishing

- Lapping

Diamond cutters


Diamond polishing

Lapping process


chapter 7 - engineering ceramics

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