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1Ceramics: Four Examples for Structural Ceramics, Chap 4

Material Science I

Ceramic Materials

F. Filser & L.J. Gauckler

ETH-Zürich, Departement Materials

[email protected]

HS 2007

Chapter 4: Four Examples for

Structural Ceramics

mailto:[email protected]


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)


Material Science I

Recommended Reading

General

• Verband der Keramischen Industrie e.V, Brevieral Technical Ceramics, ISBN 3-

924158-77-0, 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


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


Material Science I

Overview on the Properties

Resistivity 1013-1090.3-0.8 10-5>1010cm > 1014 102 –1012

Resistivity as f(T)

ALUMINA

Al2O3

ZIRCONIA

ZrO2 (3m YTZP)

NITRIDE

Si3N4

CARBIDE SiC

hp

Boroncarbide

B4C

Boronnitride

BN(hex) hp

Wolframcarbide

WC/Co

Materials Properties

Density g/cm3

3.8 6 3.3 3.2 2.52 2.3 15.8

Porosity Vol-% 0 0 0 0

Mechanical Properties

Hardness HV MPa 2000 1200 1600 2500 3200 2400

Compressive strength

MPa 1700-2500 2000 2800 2500 2760

E-modulus GPa 300-350 200 275 410-450 450 - 470 20 -100 700

Fracture toughness MPa m1/2

4 9-15 6-7 3-4 2.9 -3.7

Bending strength MPa 300 -340 800 -1400 750 -850 300 -550 50 -100 400 – 600

Thermal Properties

Melting Point °C 2450 3000 (diss)

Max. use temperature

°C 1650-1900 900-1200 1000-1400 1400-1600

Thermal expansion 10-6

K-1

7.0-9.0 8.0-11.0 3.0-4.0 4.0 5 1 – 4

Thermal conductivity W/(m K) 20-30 2-3 35 110 30 -42 20 - 30 85

Electrical Properties


Material Science I

Engineering Ceramics, Structural Ceramics, High-Tech Ceramics

(4 Examples)

• -Al2O3

• t & c + t - ZrO2

• -SiC

• -Si3N4

- modifications

- properties

- processing


Material Science I

Aluminiumoxid - Al2O3 (Alumina)


Material Science I

Characteristic Properties: - Al2O3

E

[GPa]

KIC B

[MPa]

m

[1]

3.98 400 3.4-4 400 10

Hardness

[HV10]

[10-6K-1]

Melting temperature

[°C]

2100 5.5-10 36 (RT) 2050

MPa m 3

g

cm

W

m K

Specific weight

(Density)

Elastic Modulus Stress intensity Factor

(Toughness)Bend Strength Weibull Modulus

(Reliability)

For Comparison: Metals

Weibull Modulus


Material Science I

Al2O3: Crystal Structure

Structure of -Al2O3: large circles represent oxygene, kleine

black circles are aluminium, small empty circles are non-

occupied octahedral interstices


Material Science I

-Al2O3: Structure


Material Science I

Bauxite Resources on Earth

oxygen

iron

copper

zinc

tin

silicon

magnesium

aluminium


Material Science I

Bauxite Resources on Earth


Material Science I

Aluminium Production Process

Aluminium Melting Bayer Process in detail

Bauxite Alumina Aluminium

digestor

filter

pressagitator

crushing

mill

cathode

Aluminium metal

(fluid)anode

precipitator

calcining

furnace


Material Science I

Al2O3 and Al(OH)3

Transformation Scheme for Al-Hydroxides and Aluminiumoxides


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


Material Science I

Microstructure of - Al2O3

micro-crystalline Al2O3 granular crystalline Al2O3

Al2O3 - ceramics differentiate in its microstructure, and

therefore in its properties


Material Science I

ZTA: Zirconia toughened Alumina

ZTA with 4 weight-% ZrO2.

In the SEM pictures the ZrO2 grains show up

bright due to the atomic weight difference.

4 m

(http://www.keramverband.de/brevier)


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 36

Max. Temperature of

Use (C)

1650 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

• high temperature stability

• corrosion resistance

• slow crack growth


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.


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

Crucibles

Linings, Supports, Heat ShieldsBall Valve

Pyrometer Tubes


Material Science I

Alumina Fibers – Insulation Use

(from http://www.zircarceramics.com)

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


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.


Material Science I

Zirconoxide ZrO2 (Zirconia)


Material Science I

E

[GPa]

KIC B

[MPa]

m

[1]

5.89 200 6-10 60-1000 15-25

Hardness

[HV10]

[10-6K-1]

Melting

Temperature

[°C]

1300 10 2 2680

MPa m 3

g

cm

W

m K

Characteristic Properties: ZrO2

Specific Weight

(Density)

Elastic Modulus Stress Intensity

Factor (Toughness)Bend Strength Weibull Modulus

(Reliability)


Material Science I

Phase Transformations of ZrO2

as function of temperature

Melt

↓ 2680°C

cubic

↓ 2370°C

tetragonal

↓ 1170°C

monoclinic


Material Science I

ZrO2 : Structures

The three phases of zirconoxide.

V ~ 5%


Material Science I

ZrO2 : Structures

(www.hardmaterials.de ,

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

The three phases of

zirconoxide.

http://www.hardmaterials.de/


Material Science I

ZrO2 : Lattice Parameters

Crystal System Space groupLattice

Parameters [Å]

Density

[g.cm-3]

cubica=b=c

===90

Fm3m a = 5.124 6.090

(calculated)

tetragonala=bc

===90

P42/nmc a = 5.094

c = 5.177

6.100

(calculated)

monoclinicabca

==90 >90

P21/c a = 5.156

b = 5.191

c = 5.304

= 98.9

5.830

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.

V

~ 5

%


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


Material Science I

Re-Inforcement by Micro Cracks

The energy of a progressing crack is absorbed at the micro

cracks in the microstructure.

progressing crack energy is absorbed

critical

crack


Material Science I

Stress-Induced Re-Inforcement

Stress induced transformation of meta-stable ZrO2grains in the stress field of a crack

metastabile ZrO2 grains (tetragonal)

martensitic transformed grain (monoclinic)

stress field in the vicinity of a crack tip


Material Science I

Phase Diagram of the Binary System ZrO2-Y2O3

cubic

tetragonal

monoclinic

Y2O3


Material Science I

ZrO2: Partial Stabilized Zirconia

PSZ - tetragonal segregation in a cubic matrix


Material Science I

ZrO2: Tetragonal Zirconia Polycrystals

SEM image of

3 mol% Y2O3 stabilised TZP

TEM image of

3 mol% Y2O3 stabilised TZP

200 nm


Material Science ICritcal Nucleus Radius for the

tm ZrO2 transformation vs Critical Grain Size

r critical > GS

grain doesn‟t t-m transform

r critical < GS

grain t-m transforms

G

Nu

clea

tio

n E

ner

gy,

( fr

ee e

ner

gy)

GSurface =4 r2tm

G Volume =4/3r3 Gtm

r

G

t

m

r kritisch

t

m

r critical

t

r kritisch

m

t

r critical

m

rcritical: critical nuclation radius

GS: critical grain size


Material Science I

Examples of Typical Components

milling balls with a diameter of

50 m to 25 mm


Material Science I

Zirconia in Fiber Optics Application

http://www.swiss-jewel.com

split sleeves are used in adapters

and other fiber optic components

for fiber alignment to get minimal

insertion loss of the transmitted

light signal.

ferrules and ferrule Assemblies

for fiber optic connectors or

other applications


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


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


Material Science I

Siliconcarbide SiC


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


Material Science I

Cubic structure: Zinc blende Phase diagram SiC



SiC: Structure



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.


Material Science I

Stacking variants of SiC


Material Science I

SiC Processing

SiO2 + C 1SiC + 2CO

1t + 1.4t

Mostly production of CO with an additional product SiC!!!!!


Material Science I

SiC: Acheson-Process

Acheson-furnace prior the addition of petroleum coke.

1 Ofenbett

2 Ofenkopf

3 Stromzuführung

4 Isolierschüttung

5 Seitensteine

6 Kohlenstoffkörper

1 furnace bed

2 furnace head

3 electricity inlet

4 insulating fill

5 side walls

6 graphite rod


Material Science I

SiC: Acheson-Process

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

prior the processing during the processing

graphite core

Mixture of quartz and petroleum coke

petroleum coke &

quartz

SiC-rich

layer

radially grown graphite

core


Material Science I

Further Processing Methods for SiC

Pyrolysis of methyltrichlorsilan 3 3 3CH SiCl SiC HCl

Reaction in the gas phase 4 4 4SiCl CH SiC HCl

• 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.


Material Science I

E

[GPa]

KIC B

[MPa]

m

[1]

3.2 370 3.5 390 13

Hardness

[HV10]

[10-6K-1]

Pyrolysis

[°C]

9500 4.3 100 2300

MPa m 3

g

cm

W

m K

SiC: Properties

spec. weight

(density)

Elastic Modulus Stress Intensity

Factor

Bend Strength Weibull Modulus

(Reliability)

SiC is semiconducting!

• n-conducting by means of N-dopant

• P-conducting by means of (B, Al)-dopant


Material Science I

SiC Materials and Solidification Methods

nützlicher Link: http://www.keramverband.de/

Siliconcarbide with open porosity:

• Silicate bonded SiC (microstructure)

• recrystallized SiC

(RSIC) (microstructure)

• nitride- bzw. oxynitride bonded SiC

(NSIC) (microstructure)

dense Siliconcarbide:

• reaction-bonded SiC (RBSIC)

• Silicon-infiltrated SiC (SISIC)

(microstructure)

• sintered SiC (SSIC) (microstructure)

• hot- [isostatic] pressed SiC (HPSIC

[HIPSIC]) (microstructure)

• liquid-phase sintered SiC (LPSIC)

(microstructure)

http://www.keramverband.de/brevier_engl/3/4/3/3_4_3_1.htm


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


Material Science I

SiC: Silicon Infiltrated SiC (SISIC)

SiSiC.

The metallic Silicon in the grain boundaries and pores is bright


Material Science I

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

Elastic Modulus [GPa] 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

Open Porosity [%] 25 0 1 0 0

Max. Temperature of Use [°C] 2000 1400 1700 1300 1300

SiC: Comparison of different Modifications


Material Science I

Bend Strength as Function of the Temperature

Ben

d S

tren

gth

hot pressed

sintered

“re-crystallized”

reaction-sintered

(contains free metallic Si)

ceramic bound

Temperature


Material Science I

SiC as a Semiconductor

Properties Unit Si AsGa 3C-SiC 4H-SiC 6H-SiC GaN

Lattice

constantÂ 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 / s10 10 22 20 20 22

Electron

mobilitycm2 / V s 1500 8500 1000 ? 1140 1500

Hole mobility cm2 / V s 600 400 50 120 850 ?

Breakdown

FieldMV / cm 0.3 0.6 2 3 ? 5

Thermal

ConductivityW / cm s 1.5 0.46 5.0 3.7 4.9 1.3


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

http://upload.wikimedia.org/wikipedia/de/7/7b/N-Kanal-MOSFET.png


Material Science I

SiC made of Organic Pre-cusors


Material Science I

SiC Applications

Yaimij, 1976

+1978


Material Science I

Silicon nitride Si3N4


Material Science I

E

[GPa]

KIC B

[MPa]

m

[1]

3.2 300 7 900-1200 15

Hardness

[HV10]

[10-6K-1]

Pyrolysis

[°C]

1500 3.1 25 1900

MPa m 3

g

cm

W

m K

Si3N4: Properties

spec. weight

(density)

Elastic Modulus Toughness Bend Strength Weibull Modulus

(reliability)


Material Science I

Si3N4: Structure

Structure of - and -Si3N4


Material Science I

Structural Data of different Si3N4 phases

-Si3N4

-Si3N4 (normal

powder)

Crystal System hexagonal

trigonal(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


Material Science I

Production of Si3N4

2 3 43 2 FeSi N Si N Direktnitridierung von Si

Reduktionsnitridation (Carbothermische Nitridation)

2 2 3 43 ( ) 6 ( ) 2 ( ) ( ) 6 ( )SiO S C S N G Si N S CO G

Silizium-Diimid-Route

4 3 2 4

2 3 4 3

( ) 6 ( ) ( )( ) 4

3 ( )( ) 2

SiCl G NH G Si NH G NH Cl

Si NH G Si N NH


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


Material Science I

Si3N4: Sintered Silicon Nitride

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

Sintering of Silicon nitride:

- Si3N4 + MeO (MgO) - Si3N4 + amorphous phase

(MPa)

Temperature °C1350°C

- Si3N4 + amorphous phase

1100°C

Metal


Material Science I

SiAlONe = Mixed Crystals (Solid Solutions) of Si3N4

Si-Al-O-N system with

its reciprocal salt system:

Si3N4-4AlN-2Al2O3-3SiO2.

Idea: temporary amorphous phase


Material Science I

The SiAlONe = Mixed Crystals (solid solutions) of Si3N4

)12()12()12()12()12()12()12(4

)12(3

232324

OSiOAlNAlNSi

3 4 2 3 24 2 3Si N AlN Al O SiO

Si3N4 4AlN

2Al2O33SiO2


Material Science I

Order of the System

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 .

N = Number of Components in the System;

P = Number of Phases

f = Number of Degrees of Freedom

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


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!


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


Material Science I

The SiAlBeONe = Mixed Crystalls (solid solutions) of Si3N4


Material Science I

Seeds for Controlling the Microstructure

with seeds

without seeds

without seeds

with seeds -> most columnar crystals in (a) , less

columnar crystals in (b) and (c)


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.


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)


Material Science I

Si3N4: Creep at Elevated Temperature

creep velocity = deformation speed

at elevated temperature as function of the mechanical stress.

Stress

Sta

tionar

y c

reep

vel

oci

ty

RBSN

dense SN

RBSN:

- grain boundaries without glass phase

- less strength

- less creep velocity

Dense SN:

- grain boundaries with glass phase

- higher strength

- higher creep velocity


Material Science I

Comparison of the - Si3N4 Materials Properties

RBSNSi+N2Si3N4+p

ores

SSNsintered

HPSNhot 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


Material Science I

More Ceramics for Structural Applications

• Boron nitride (BN)

• Boron carbide (B4C)

• Tungsten carbide (WC)

• Carbon (diamond, graphite)


Material Science I

Hardness as Function of the Temperature

Hard

nes

s (H

V)

1 / Temperature (°C-1)

Diamond (CC)

Cubic Boron Nitride (BNC)

Corundum (Al2O3)

(Tetra-) Boron carbide (B4C)


Material Science I

“Hardmetal” WC/Co

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


Material Science I

Comparison: Ceramic – Metal - Polymer


Material Science I

Summary


Material Science I

Additional Slides


Material Science I

Properties of Non-Oxide Materials


Material Science I

Comparison: Metals

Aluminum

Iron

Copper

Nickel

TantalTitan

Tungsten

Met

al

Ch

em. S

ym

bol

Ato

mic

No.

Den

sity

(g/c

m3)

Mel

tin

g T

emp

.

(°C

)

Boil

ing T

emp

.

(°C

)

Ten

sile

Str

ength

N/m

m2)

Bri

nel

l H

ard

nes

s

Vic

ker

s H

ard

nes

s

Elo

ngati

on

aft

er

fract

ure

(%

)


Material Science I

Resistivity as Function of the Temperature (hex BN)


Material Science I

Aluminium Melting

Electrical current

supply

Alumina

Cryolite

Carbon anodes

Alumina

Crust

fluidicAlumina

Carbon cathode

Melt: 950 °C


Material Science I

Bayer Prozess


Material Science I

Strength distribution within Production Batches

Strength

Metal

Ceramic

Fre

quen

cy

K, M - average value of the strength


Material Science I

Zincblende structure: ZnS


Material Science I

Phase diagram of the Si-C – System


Material Science I

SiC Materials and Compaction Methods

Open porous silicon carbide:

• silicate-bonded

silicon carbide

• Re-crystallized

silicon carbide (RSIC)

• nitride or oxynitride bonded

silicon carbide (NSIC)

Dense silicon carbide:

• reaction-bonded

silicon carbide (RBSIC)

• silicon-infiltrated

silicon carbide (SISIC)

• 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)

http://www.keramverband.de/brevier_engl



Material Science I

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

Microstructure of coarse

grained silicate-bonded SiC

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



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




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




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




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




Material Science I

Nitride-bonded SiC (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.

Microstructure of NSIC




Material Science I

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