Ceramic Materials Chapter 4: Four Examples for Structural Ceramics

Material Science I

Ceramic Materials

Chapter 4: Four Examples for Structural Ceramics F. Filser & L.J. Gauckler ETH-Zürich, Departement Materials [email protected]

HS 2007

Ceramics: Four Examples for Structural Ceramics, Chap 4

1

Material Science I

Goal for your Understanding •

Four Examples: – – – –

-Al2O3 t & c + t - ZrO2 -SiC  -Si3N4

•

Important ceramics which may be applied in structural applications

•

We take a look at

•

–

their composition (chemical and phases)

–

their processing

–

their microstructure

–

their properties

The mechanical properties of these ceramic materials served also as

the basis for the development of our today’s picture of failure mechanics of brittle materials and its basic mathematical description. (see chapter 6, in spring term) Ceramics: Four Examples for Structural Ceramics, Chap 4

2

Material Science I

Recommended Reading General •

Verband der Keramischen Industrie e.V, Brevieral Technical Ceramics, ISBN 3924158-77-0, Fahner Verlag, 2004

•

G. Kostorz (ed), High-Tech Ceramics: Viewpoints and Perspectives, Academic Press, 1989

•

Ichinose Wataru, Introduction to Fine Ceramics, Wiley, 1987

Alumina

•

Dorre, E.; Hubner, H., Alumina: Processing, Properties, and Applications, SpringerVerlag, 1984, pp. 329, 1984 9

Zirconia •

Stevens, R, Zirconia and Zirconia Ceramics, Second Edition, Magnesium Elektron Ltd., 1986, pp. 51, 1986

•

RC Garvie, Stabilization of the tetragonal structure in zirconia microcrystals, The Journal of Physical Chemistry, 1978

•

HGM Scott, Phase relationships in the zirconia-yttria system, Journal of Materials Science, Springer, 1975


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Material Science I

Recommended Reading Silicon based Ceramics (SiC, Si3N4)

•

Stephen C. Danforth (Editor), Brian W. Sheldon, Silicon-Based Structural Ceramics (Ceramic Transactions), American Ceramic Society, 2003,

•

Shigeyuki Somiya (Editor), M. Mitomo (Editor), M. Yoshimura (Editor), Silicon Nitride-1, Kluwer Academic Publishers, 1990

SiAlON •

Thommy Ekström and Mats Nygren, SiAION Ceramics, J Am Cer Soc Volume 75 Page 259 - February 1992

•

Boskovic and L.J. Gauckler, Formation of beta -Si3N4 solid solutions in the system Si, Al, O, N by reaction sintering--sintering of an Si3N4 , AlN, Al2O3 mixture, La Ceramica (Florence), Vol. 33, no. N-2, pp. 18-22. 1980


4

Material Science I

Overview on the Properties ALUMINA

ZIRCONIA

NITRIDE

Al2O3

ZrO2 (3m YTZP)

Si3N4

CARBIDE SiC

Boroncarbide

Boronnitride

Wolframcarbide

hp

B4C

BN(hex) hp

WC/Co

2.52

2.3

15.8

Materials Properties 3

Density

g/cm

3.8

6

3.3

3.2

Porosity

Vol-%

0

0

0

0

Hardness HV

MPa

2000

1200

1600

2500

3200

Compressive strength

MPa

1700-2500

2000

2800

2500

2760

E-modulus

GPa

300-350

200

275

410-450

450 - 470

4

9-15

6-7

3-4

2.9 -3.7

300 -340

800 -1400

750 -850

300 -550

Mechanical Properties

Fracture toughness

MPa m

Bending strength

MPa

1/2

2400

20 -100

700

50 -100

400 – 600

Thermal Properties Melting Point

°C

Max. use temperature

°C

Thermal expansion Thermal conductivity

2450

3000 (diss)

1650-1900

900-1200

10 K

7.0-9.0

8.0-11.0

3.0-4.0

4.0

5

1–4

W/(m K)

20-30

2-3

35

110

30 -42

20 - 30

-6

-1

1000-1400 1400-1600

85

Electrical Properties Resistivity

cm

> 1014

>1010


102 –1012

0.3-0.8

1013-109

Resistivity as f(T)

10-5

5

Material Science I

Engineering Ceramics, Structural Ceramics, High-Tech Ceramics (4 Examples)

• -Al2O3 • t & c + t - ZrO2 • -SiC •  -Si3N4 - modifications - properties - processing


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Material Science I

Aluminiumoxid - Al2O3 (Alumina)


7

Material Science I

Characteristic Properties:  - Al2O3 Specific weight (Density)

Elastic Modulus



Stress intensity Factor (Toughness)

E [GPa]

 g   cm3    3.98

400

Hardness [HV10]

 [10-6K-1]

2100

5.5-10

KIC

MPa m    3.4-4 

 W  m K   

36 (RT)

Bend Strength

Weibull Modulus (Reliability)

B [MPa]

m [1]

400

10

Melting temperature [°C]

2050

For Comparison: Metals Ceramics: Four Examples for Structural Ceramics, Chap 4

Weibull Modulus

8

Material Science I

Al2O3: Crystal Structure

Structure of -Al2O3: large circles represent oxygene, kleine black circles are aluminium, small empty circles are nonoccupied octahedral interstices


9

Material Science I

-Al2O3: Structure


10

Material Science I

Bauxite Resources on Earth

oxygen silicon aluminium iron magnesium copper zinc tin


11

Material Science I

Bauxite Resources on Earth


12

Material Science I

Aluminium Production Process Aluminium metal (fluid)

precipitator anode crushing mill

agitator

calcining furnace

filter press

digestor cathode

Bauxite

Alumina


Aluminium Melting

Aluminium

Bayer Process in detail

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Material Science I

Al2O3 and Al(OH)3

Transformation Scheme for Al-Hydroxides and Aluminiumoxides Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Microstructure of - Al2O3

• normal grain size of good and pure Al2O3: 5-10 m • Al2O3 with glass phase may possess up to 100 m grain size and a second phase in the grain boundaries Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Microstructure of - Al2O3

micro-crystalline Al2O3

granular crystalline Al2O3

Al2O3 - ceramics differentiate in its microstructure, and therefore in its properties Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

ZTA: Zirconia toughened Alumina

4 m ZTA with 4 weight-% ZrO2. In the SEM pictures the ZrO2 grains show up bright due to the atomic weight difference.

(http://www.keramverband.de/brevier) Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Properties of Zirconia Toughened Alumina (15% zirconia-85% alumina) in comparison to Al2O3

Properties

ZTA Al2O3

Density (g.cm-3)

4.1

3.98

Elastic Modul (GPa)

310

400

Bend strength (MPa)

760

400

Stress Intensity Factor Kic (MPa.m0.5)

6 – 12

3-4

Vickers Hardness (Hv)

1750

2100

Thermal Expansion Coefficient (x10-6/C)

8.1

5.5 - 10

Thermal Conductivity (W/m.K)

23

Max. Temperature of Use (C)

1650

The addition of zirconia to the alumina matrix increases fracture toughness easily by two times and can be improved by as high as four times, while strength is more than doubled. Key Properties

• excellent mechanical properties • wear resistance

36

• high temperature stability • corrosion resistance


1650

• slow crack growth 18

Material Science I

Hip Joint Prosthesis – Femoral Head made of Al2O3

Modular hip joint system : acetabulum socket (left) and femoral heads (middle) made of alumina. Right side shows sockets made of polyethylen, and in between two different types of metal stems. Note the components have different size and shape to fit best the individual situation. Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Products made of Al2O3

Lining for a drum mill, up to 300 liters, D1 up to 800 mm, height up to 1000 mm, weight 250 kg

Pyrometer Tubes

Crucibles

Ball Valve Ceramics: Four Examples for Structural Ceramics, Chap 4

Linings, Supports, Heat Shields

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Material Science I

Alumina Fibers – Insulation Use

Alumina Papers • flexible and rigid grades of high alumina fiber paper in sheets, full rolls and die cut parts • useful to temperatures as high as 1650°C.

Alumina Mat • layered, low density flexible mat • 100% polycrystalline alumina fiber • useful up to temperatures as high as 1650°C • used as fill between rigid insulation materials

Alumina Blanket • quilted alumina fiber blanket • good handleability, easily cut • very low thermal conductivity. • max temperature of use is 1600° C

(from http://www.zircarceramics.com) Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

General Typical Properties and Use of Al2O3 •

• • •

high strength and hardness, temperature stability, high wear resistance at high temperatures, and good corrosion resistance at high temperatures


• • • •

• • • •

in the sanitary industry as a sealing element, in electrical engineering as insulation, in electronics as a substrate, in machine and plant construction as wear protection in the chemical industry as corrosion protection in instrumentation as a protective tube for thermocouples used for high temperature in human medicine as an implant, and in high temperature applications as a burner nozzle or as a support tube for heat conductors.

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Material Science I

Zirconoxide ZrO2 (Zirconia)


23

Material Science I

Characteristic Properties: ZrO2 Specific Weight (Density)

Elastic Modulus

Stress Intensity Factor (Toughness)

Bend Strength




E [GPa]

KIC

B [MPa]

m [1]

60-1000

15-25

 g   cm3   

5.89

200

Hardness [HV10]

 [10-6K-1]

1300

10


MPa m   

6-10   W  m K   

Melting Temperature [°C]

2

2680

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Material Science I

Phase Transformations of ZrO2 as function of temperature Melt ↓

2680°C

cubic

↓

2370°C

tetragonal ↓

1170°C

monoclinic


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Material Science I

ZrO2 : Structures

V ~ 5%

The three phases of zirconoxide. Ceramics: Four Examples for Structural Ceramics, Chap 4

26

Material Science I

ZrO2 : Structures

The three phases of zirconoxide.

(www.hardmaterials.de , Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000) Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Crystal System

Space group

Lattice Parameters [Å]

Density [g.cm-3]

cubic

Fm3m

a = 5.124

6.090 (calculated)

P42/nmc

a = 5.094 c = 5.177

6.100 (calculated)

P21/c

a = 5.156 b = 5.191 c = 5.304  = 98.9

5.830

a=b=c ===90

tetragonal a=bc ===90

monoclinic abca

==90 >90

V ~ 5%

ZrO2 : Lattice Parameters

Structural data of ZrO2 phases. The transformation cubic – tetragonal causes a small change in lattic parameters, however the transformation tetragonal – monoclinic the density and lattice parameters change significantly.


28

Material Science I

Re-inforcement Mechanisms in zirconoxide derived ceramic materials

• stress-induced transformation re-inforcement • stress-induced Micro Crack re-inforcement • spontaneous micro crack re-inforcement • crack deflection / deviation


29

Material Science I

Re-Inforcement by Micro Cracks

progressing crack

energy is absorbed

critical crack

The energy of a progressing crack is absorbed at the micro cracks in the microstructure.


30

Material Science I

Stress-Induced Re-Inforcement

metastabile ZrO2 grains (tetragonal)

martensitic transformed grain (monoclinic) stress field in the vicinity of a crack tip

Stress induced transformation of meta-stable ZrO2 grains in the stress field of a crack Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Phase Diagram of the Binary System ZrO2-Y2O3 cubic

tetragonal

monoclinic

Y2O3


32

Material Science I

ZrO2: Partial Stabilized Zirconia

PSZ - tetragonal segregation in a cubic matrix


33

Material Science I

ZrO2: Tetragonal Zirconia Polycrystals

200 nm

SEM image of 3 mol% Y2O3 stabilised TZP


TEM image of 3 mol% Y2O3 stabilised TZP

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Material Science I

Critcal Nucleus Radius for the tm ZrO2 transformation vs Critical Grain Size

r critical < GS grain t-m transforms



r critical kritisch

r critical > GS grain doesn‟t t-m transform

r critical kritisch



m t

m t

rcritical: critical nuclation radius GS: critical grain size Ceramics: Four Examples for Structural Ceramics, Chap 4

G Nucleation Energy,( free energy)

G

GSurface =4 r2tm

r

G Volume =4/3r3 Gtm 35

Material Science I

Examples of Typical Components

milling balls with a diameter of 50 m to 25 mm


36

Material Science I

Zirconia in Fiber Optics Application

ferrules and ferrule Assemblies for fiber optic connectors or other applications

split sleeves are used in adapters and other fiber optic components for fiber alignment to get minimal insertion loss of the transmitted light signal.

http://www.swiss-jewel.com Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

ATZ – Alumina Toughened Zirconia name elements composition density open porosity grain size (mli) Vickers hardness Mohs hardness compaction strength bend strength elastic modulus stress intensity factor K1C Poisson number max. temperature of use mean TEC (20-1000°C) * thermal conductivity specific heat capacity

*) mean thermal expansion coefficient


38

Material Science I

General Typical Properties of Zirconia

• • • • • • •

high fracture toughness, thermal expansion similar to cast iron, extremely high bending strength and tensile strength, high resistance to wear and to corrosion, low thermal conductivity oxygen ion conductivity and very good tribological properties


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Material Science I

Siliconcarbide SiC


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Material Science I

Comparison of different Silicon Compounds

SiO2

Si3N4

SiC

Difference of Electronegativity

1.54

1.14

0.65

Amount of covalent Bonding [%]

68

75

85

Enthalpy of Formation Hf° [kcal/mol]

-217

-178

-15


41

Material Science I

SiC: Structure

Cubic structure: Zinc blende


Phase diagram SiC (www.hardmaterials.de , Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000)

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Material Science I

Polytypes of SiC

Unit cell of hexagonal Polytypes of SiC: a1=a2=a3


Atomic positions and bondings for the 2H-SiC unit cell.

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Material Science I

Stacking variants of SiC


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Material Science I

SiC Processing

SiO2 + C  1SiC + 2CO 1t + 1.4t Mostly production of CO with an additional product SiC!!!!!


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Material Science I

SiC: Acheson-Process

11 Ofenbett furnace bed 22 Ofenkopf furnace head 33 Stromzuführung electricity inlet 44 Isolierschüttung insulating fill 55 Seitensteine side walls 66 Kohlenstoffkörper graphite rod

Acheson-furnace prior the addition of petroleum coke. Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

SiC: Acheson-Process during the processing

prior the processing

petroleum coke & quartz

SiC-rich layer

graphite core Mixture of quartz and petroleum coke

radially grown graphite core

Cross section of an Acheson-furnance prior and after the processing reaction.


47

Material Science I

Further Processing Methods for SiC

Pyrolysis of methyltrichlorsilan

Reaction in the gas phase

CH3 SiCl3     SiC  3HCl

SiCl4  CH 4     SiC  4HCl

• These routes are very expensive and have a high enviromental impact

• but they produce powders which are factor 10 smaller than the Acheson process does.


48

Material Science I

SiC: Properties spec. weight (density)

Elastic Modulus

  g   cm3   

3.2

Stress Intensity Factor

E [GPa]

KIC MPa m   

370

3.5

Hardness [HV10]

 [10-6K-1]

9500

4.3

  W  m K   

100

Bend Strength


B [MPa]

m [1]

390

13

Pyrolysis [°C]

2300

SiC is semiconducting! • n-conducting by means of N-dopant • P-conducting by means of (B, Al)-dopant Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

SiC Materials and Solidification Methods

Siliconcarbide with open porosity:

dense Siliconcarbide:

• Silicate bonded SiC (microstructure)

• reaction-bonded SiC (RBSIC)

• recrystallized SiC (RSIC) (microstructure)

• Silicon-infiltrated SiC (SISIC) (microstructure)

• nitride- bzw. oxynitride bonded SiC (NSIC) (microstructure)

• sintered SiC (SSIC) (microstructure) • hot- [isostatic] pressed SiC (HPSIC [HIPSIC]) (microstructure) • liquid-phase sintered SiC (LPSIC) (microstructure)

nützlicher Link: http://www.keramverband.de/ Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

SiC: Liquid Phase Sintered SiC (LPSIC)

Liquid Phase Sintered SiC, etched. The amorphous phase in the grainboundaries is bright color, hence is Al or Si-rich silicat Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

SiC: Silicon Infiltrated SiC (SISIC)

SiSiC. The metallic Silicon in the grain boundaries and pores is bright Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

SiC: Comparison of different Modifications Reaction bonded SiC

Si inflitrated SiC

Sintere d SiC

HP SiC

HIP SiC

Density [g/cm3]

2.5-2.9

3.10

3.15

3.20

3.21

Bend Strength [MPa]

80-100

400

500

600-700

600-700

240

370

390

420

450

Stress Intensity Factor KIC MPa m1/2

-

3-4

4-5

5-6

5-6

Weibull Modulus [1]

-

10

10

10

10-15

Heat conduction [W/mK]

-

120

70

90

90-120

Thermal Expansion Coeff. [10-6K-1]

4.5

4.4

4.5

4.6

4.5

Spec. Electrical Resistance cm-1

1011

10

103

105

105

25

0

1

0

0

2000

1400

1700

1300

1300

Elastic Modulus [GPa]

Open Porosity [%] Max. Temperature of Use [°C]


53

Material Science I

Bend Strength as Function of the Temperature

hot pressed

Bend Strength

sintered

reaction-sintered (contains free metallic Si)

“re-crystallized” ceramic bound

Temperature


54

Material Science I

SiC as a Semiconductor Properties

Unit

Si

AsGa

3C-SiC

4H-SiC

6H-SiC

GaN

Lattice constant

Â

5.43

5.65

4.36

3.073

3.08

4.51

Band gap

eV

1.1

1.4

2.4

3.3

3.0

3.4

Saturation electron velocity

106 cm / s

10

10

22

20

20

22

Electron mobility

cm2 / V s

1500

8500

1000

?

1140

1500

Hole mobility

cm2 / V s

600

400

50

120

850

?

Breakdown Field

MV / cm

0.3

0.6

2

3

?

5

Thermal Conductivity

W / cm s

1.5

0.46

5.0

3.7

4.9

1.3


55

Material Science I

SiC as a Semiconductor SiC is an enabling material for a variety of new semiconductor devices: • high-power high-voltage switching applications, • high temperature electronics, and • high power microwave applications in the 1 - 10 GHz regime. Enabling SiC-Properties:

• extreme thermal stability, • wide bandgap energy (3.0 eV and 3.25 eV for the 6H and 4H polytypes respectively), • leakage currents in SiC are many orders of magnitude lower than in silicon (wide bandgap) and • high breakdown field (8x higher than for Si) • is the only compound semiconductor which can be thermally oxidized to form a high quality native oxide (SiO2) which make it possible to fabricate MOSFETs*.

*MOSFET: Metal Oxide Semiconductor (auch: Silicon) Field Effect Transistor


56

Material Science I

SiC made of Organic Pre-cusors


57

Material Science I

SiC Applications

Yaimij, 1976 +1978


58

Material Science I

Silicon nitride Si3N4


59

Material Science I

Si3N4: Properties spec. weight (density)

Elastic Modulus

  g   cm3   

3.2

Toughness

E [GPa] 300

Hardness [HV10]

 [10-6K-1]

1500

3.1


KIC MPa m   

7   W  m K   

25

Bend Strength

Weibull Modulus (reliability)

B [MPa]

m [1]

900-1200

15

Pyrolysis [°C]

1900

60

Material Science I

Si3N4: Structure

Structure of - and -Si3N4


61

Material Science I

Si3N4: Structure

Structure of - and -Si3N4


(www.hardmaterials.de , Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000)

62

Material Science I

Structural Data of different Si3N4 phases -Si3N4

-Si3N4 (normal powder)

trigonal hexagonal

(same axe conditions as hexagonal, however higher symmetry)

Space group

P 63/m

P 31c

Lattice parameters [Å]

a=7.61 c=2.91

a=7.76 c=5.62

Density (calculated)

3.912

3.183

N-self diffusion at 1450°C [cm-2s-1]

10-15

10-19

Crystal System


63

Material Science I

Production of Si3N4

Direktnitridierung von Si

Fe 3Si  2 N2   Si3 N4

Reduktionsnitridation (Carbothermische Nitridation)

3SiO2 (S )  6C (S )  2 N2 (G)   Si3 N4 (S )  6CO(G) Silizium-Diimid-Route

SiCl4 (G)  6 NH 3 (G)   Si ( NH 2 )(G)  4 NH 4Cl 3Si( NH 2 )(G)   Si3 N 4  2 NH 3


64

Material Science I

- Si3N4: Sintered Silicon Nitride in situ “short fibre re-inforced material”  high toughness

etched failure surface of a component made of SSN


65

Material Science I

Si3N4: Sintered Silicon Nitride

Sintering of Silicon nitride:

- Si3N4 + MeO (MgO)  - Si3N4 + amorphous phase - Si3N4 + amorphous phase

 (MPa) Metal

Temperature °C

1100°C 1350°C

Schliff aus SSN. Die hellen Bereiche stellen die oxidnitridische Glasphase dar


66

Material Science I

SiAlONe = Mixed Crystals (Solid Solutions) of Si3N4 Idea: temporary amorphous phase

Si-Al-O-N system with its reciprocal salt system: Si3N4-4AlN-2Al2O3-3SiO2.


67

Material Science I

The SiAlONe = Mixed Crystals (solid solutions) of Si3N4 2Al2O3

3SiO2

Si3N4

(12 ) (12 ) Si3 N4

 4 Al

(12 )

N

(12 )

 2 Al

(12 ) 2

4AlN

O

(12 ) 3

 3Si

(12 )

O

(12 ) 2

Si3 N4  4 AlN  2 Al2O3  3SiO2 Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Order of the System N = Number of Components in the System; P = Number of Phases f = Number of Degrees of Freedom Actually:

Si Al O N 1 + 1 + 1 + 1 = 4 components = „4 – materials“ system

but we only look at specimen with Si4+ and

Al3+ and

O2- and

N3- valency.

(limitation to a plane). This equally means no change of valency, and hence no phases with Al2+ or Si1+ etc. valency . In analogy to the mechanics the number of independent variables to describe the system is called „Degrees of Freedom“ of the system. The Gibbs„ Phase Rule is: P+F=K+2 P = Number of Phases, here = 4 F = Number of the Degrees of Freedom K = Number of System Components


69

Material Science I

The -SiAlONe: isothermal cross section at 1800°C of the System Si3N4-4AlN-2Al2O3-3SiO2 showing the -Si6-xAlxOxN8-x solid solution

-Si6-xAlxOxN8-x Solid Solution (ss) For all x the cat/an-ion ratio is equal to 3:4. Therefore we dont have keine holes but a substitutional solid solution. That means that the solid solution will be found only (!) on that line and no extension perpendicular to that line!


70

Material Science I

The SiAlON‘s of the 1800°C isothermal cross section of the Si3N4-4AlN-2Al2O3-3SiO2 system with the -Si6-xAlxOxN8-x solid solution


71

Material Science I

The SiAlBeONe = Mixed Crystalls (solid solutions) of Si3N4


72

Material Science I

Seeds for Controlling the Microstructure

with  seeds

with seeds

without seeds

without seeds


-> most columnar crystals in (a) , less columnar crystals in (b) and (c) 73

Material Science I

The SiAlONe = Mixed Crystalls (solid solutions) of Si3N4 Crack deflection in material (a) with the columnar microstructure is clearly visible, and therefore high toughness (KIC) values results.


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Material Science I

-SiAlONe = Mixed Crystalls (solid solutions) of - Si3N4

Anatoly Rosenflanz and I-Wei Chen: Phase Relationships and Stability of -SiAlON, J. Am. Ceram. Soc., 82 [4] 1025–36 (1999) Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Si3N4: Creep at Elevated Temperature

Stationary creep velocity

Stress 

dense SN

RBSN

creep velocity



RBSN: - grain boundaries without glass phase - less strength - less creep velocity Dense SN: - grain boundaries with glass phase - higher strength - higher creep velocity

= deformation speed

at elevated temperature as function of the mechanical stress. Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I

Comparison of the  - Si3N4 Materials Properties

RBSN

SSN

HPSN

Si+N2Si3N4+p ores

sintered

hot pressed

relative Density [%]

65-85

95-100

98-100

Bend Strength at RT [MPa]

200-350

700-1400

700-1500

KIC [MPa m1/2]

1.5-3

5-12

5-12

Hardness [GPa]

5-10

14-18

14-18

Heat Conductivity (W/mK)

4-15

20-40

20-40

Thermal Expansion Coeff. [10-6 K-1]

2.5-3

2.5-3.8

2.5-3.8


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Material Science I

More Ceramics for Structural Applications

• Boron nitride (BN)

• Boron carbide (B4C) • Tungsten carbide (WC) • Carbon (diamond, graphite)


78

Material Science I

Hardness as Function of the Temperature

Hardness (HV)

Diamond (CC) Cubic Boron Nitride (BNC) (Tetra-) Boron carbide (B4C) Corundum (Al2O3)

1 / Temperature (°C-1)


79

Material Science I

“Hardmetal” WC/Co

Tungsten carbide grains (90-94%) in a Cobalt matrix (6-10%)


80

Material Science I

Comparison: Ceramic – Metal - Polymer


81

Material Science I

Summary


82

Material Science I

Summary


83

Material Science I

Additional Slides


84

Material Science I

Properties of Non-Oxide Materials


85

Ceramics: Four Examples for Structural Ceramics, Chap 4 Brinell Hardness Vickers Hardness

Elongation after fracture (%)

Tensile Strength N/mm2)

Boiling Temp. (°C)

Melting Temp. (°C)

Density (g/cm3)

Atomic No.

Chem. Symbol

Metal

Material Science I

Comparison: Metals

Aluminum

Iron

Copper

Nickel

Tantal Titan

Tungsten

86

Material Science I

Resistivity as Function of the Temperature (hex BN)


87

Material Science I

Aluminium Melting

Carbon anodes

Alumina Cryolite

Alumina Crust

Melt: 950 °C fluidicAlumina Carbon cathode

Electrical current supply


88

Material Science I

Bayer Prozess


89

Material Science I

Strength distribution within Production Batches

K, M - average value of the strength

Frequency

Metal

Ceramic

Strength


90

Material Science I

Zincblende structure: ZnS


91

Material Science I

Phase diagram of the Si-C – System


92

Material Science I

SiC Materials and Compaction Methods Open porous silicon carbide:

Dense silicon carbide:

•

silicate-bonded silicon carbide

•

reaction-bonded silicon carbide (RBSIC)

•

Re-crystallized silicon carbide (RSIC)

•

silicon-infiltrated silicon carbide (SISIC)

•

nitride or oxynitride bonded silicon carbide (NSIC)

•

sintered silicon carbide (SSIC)

•

hot [isostatic] pressed silicon carbide (HPSIC, [HIPSIC])

•

liquid-phase sintered silicon carbide (LPSIC)

(from: http://www.keramverband.de/brevier_engl, Breviary Technical Ceramics, Verband der Keramischen Industrie)


93

Material Science I

Silicate-bonded SiC

Microstructure of coarse grained silicate-bonded SiC

Microstructure of fine grained silicate-bonded SiC

• manufactured from coarse and medium grained SiC powders, sintered with 5 to 15 % aluminosilicate binder in air at about 1400°C. • strength, corrosion resistance, and high-temperature characteristics, are determined by the silicate binding matrix, and lie below those of non-oxide bonded SiC ceramics as the binding matrix begins to soften at very high application temperatures • advantage: comparatively low manufacturing cost. • applications for this material include, for example, plate stackers used in the porcelain firing


(from: http://www.keramverband.de/brevier_engl)

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Material Science I

Liquid-Phase Sintered SiC (LPSIC)

Microstructure of LPSIC • dense material containing SiC, a mixed oxynitride SiC phase, and an oxide secondary phase. • Manufactured from silicon carbide powder and various mixtures of oxide ceramic powders, often based on aluminium oxide. • components are compressed in a pressure sintering procedure at a pressure of 20-30 MPa and a temperature of more than 2,000°C. • dense, practically pore-free material showing high strength and high toughness Ceramics: Four Examples for Structural Ceramics, Chap 4


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Material Science I

(Pressureless) Sintered SiC (SSIC)

Microstructure of SSIC

Microstructure of coarse grained SSIC

• produced using very fine SiC powder containing sintering additives (B,C, Al, Al-compounds). It is processed using forming methods typical for other ceramics and sintered at 2,000 to 2,200° C in an inert gas atmosphere. • fine-grained versions with grain sizes < 5 um, coarse-grained versions with grain sizes of up to 1.5 mm • high strength that stays nearly constant up to very high temperatures (approximately 1,600° C), maintaining that strength over long periods Ceramics: Four Examples for Structural Ceramics, Chap 4


96

Material Science I

Reaction-Bonded Silicon-Infiltrated SiC (RBSIC / SISIC)

Microstructure of SISIC

Microstructure of coarse grained SISIC

• This is achieved by infiltrating a formed part of silicon carbide and carbon with metallic silicon. The reaction between the liquid silicon and the carbon leads to SiC bonding between SiC grains. The remaining pore volume is filled with metallic silicon. • No shrinkage takes place, hence unusually large parts with very precise dimensions are possible max temperature of use is limited to ca 1,380° C due to the melting point of metallic silicon • is composed of approximately 85 to 94 % SiC and correspondingly 15 to 6 % metallic silicon (Si). SISIC has practically no residual prorosity Ceramics: Four Examples for Structural Ceramics, Chap 4


97

Material Science I

Re-crystallized silicon carbide (RSIC)

Microstructure of RSIC • pure silicon carbide material with approximately 11 to 15 % open porosity • sintered at very high temperatures from 2,300 to 2,500° C, at which the mix of extremely fine and coarse grains is converted to a compact SiC matrix without shrinkage • possesses lower strength and outstanding thermal shock resistance in comparison to dense silicon carbide ceramics due to its open porosity • maximum temperature of use is up to 1650°C (from: http://www.keramverband.de/brevier_engl) Ceramics: Four Examples for Structural Ceramics, Chap 4

98

Material Science I

Nitride-bonded SiC (NSIC)

Microstructure of NSIC • A moulded body of silicon carbide granulate and metallic silicon powder is being nitrided in an atmosphere of nitrogen at approx. 1,400 °C. The initially metallic silicon changes to silicon nitride, creating a bond between the silicon carbide grains. Then the material is exposed to an oxidising atmosphere at a temperature above 1,200 °C where a thin glassy oxidation layer is created. • NSiC is a porous material (10 to15 vol-% porosity from which are 1 to 5 vol-% is open porosity), • NSiC is sintered shrinkage-free. (from: http://www.keramverband.de/brevier_engl) Ceramics: Four Examples for Structural Ceramics, Chap 4

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Material Science I


100