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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
HS 2007
Chapter 4: Four Examples for
Structural Ceramics
2Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
3Ceramics: Four Examples for Structural Ceramics, Chap 4
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
4Ceramics: Four Examples for Structural Ceramics, Chap 4
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
5Ceramics: Four Examples for Structural Ceramics, Chap 4
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
6Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Engineering Ceramics, Structural Ceramics, High-Tech Ceramics
(4 Examples)
• -Al2O3
• t & c + t - ZrO2
• -SiC
• -Si3N4
- modifications
- properties
- processing
7Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Aluminiumoxid - Al2O3 (Alumina)
8Ceramics: Four Examples for Structural Ceramics, Chap 4
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
9Ceramics: Four Examples for Structural Ceramics, Chap 4
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
10Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
-Al2O3: Structure
11Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Bauxite Resources on Earth
oxygen
iron
copper
zinc
tin
silicon
magnesium
aluminium
12Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Bauxite Resources on Earth
13Ceramics: Four Examples for Structural Ceramics, Chap 4
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
14Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Al2O3 and Al(OH)3
Transformation Scheme for Al-Hydroxides and Aluminiumoxides
15Ceramics: Four Examples for Structural Ceramics, Chap 4
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
16Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Microstructure of - Al2O3
micro-crystalline Al2O3 granular crystalline Al2O3
Al2O3 - ceramics differentiate in its microstructure, and
therefore in its properties
17Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
18Ceramics: Four Examples for Structural Ceramics, Chap 4
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
19Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
20Ceramics: Four Examples for Structural Ceramics, Chap 4
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
21Ceramics: Four Examples for Structural Ceramics, Chap 4
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
22Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
23Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Zirconoxide ZrO2 (Zirconia)
24Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
25Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Phase Transformations of ZrO2
as function of temperature
Melt
↓ 2680°C
cubic
↓ 2370°C
tetragonal
↓ 1170°C
monoclinic
26Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
ZrO2 : Structures
The three phases of zirconoxide.
V ~ 5%
27Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
ZrO2 : Structures
(www.hardmaterials.de ,
Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000)
The three phases of
zirconoxide.
28Ceramics: Four Examples for Structural Ceramics, Chap 4
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
%
29Ceramics: Four Examples for Structural Ceramics, Chap 4
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
30Ceramics: Four Examples for Structural Ceramics, Chap 4
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
31Ceramics: Four Examples for Structural Ceramics, Chap 4
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
32Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Phase Diagram of the Binary System ZrO2-Y2O3
cubic
tetragonal
monoclinic
Y2O3
33Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
ZrO2: Partial Stabilized Zirconia
PSZ - tetragonal segregation in a cubic matrix
34Ceramics: Four Examples for Structural Ceramics, Chap 4
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
35Ceramics: Four Examples for Structural Ceramics, Chap 4
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
36Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Examples of Typical Components
milling balls with a diameter of
50 m to 25 mm
37Ceramics: Four Examples for Structural Ceramics, Chap 4
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
38Ceramics: Four Examples for Structural Ceramics, Chap 4
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
39Ceramics: Four Examples for Structural Ceramics, Chap 4
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
40Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Siliconcarbide SiC
41Ceramics: Four Examples for Structural Ceramics, Chap 4
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
42Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Cubic structure: Zinc blende Phase diagram SiC
(www.hardmaterials.de ,
Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000)
SiC: Structure
43Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
44Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Stacking variants of SiC
45Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
SiC Processing
SiO2 + C 1SiC + 2CO
1t + 1.4t
Mostly production of CO with an additional product SiC!!!!!
46Ceramics: Four Examples for Structural Ceramics, Chap 4
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
47Ceramics: Four Examples for Structural Ceramics, Chap 4
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
48Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
49Ceramics: Four Examples for Structural Ceramics, Chap 4
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
50Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
51Ceramics: Four Examples for Structural Ceramics, Chap 4
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
52Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
SiC: Silicon Infiltrated SiC (SISIC)
SiSiC.
The metallic Silicon in the grain boundaries and pores is bright
53Ceramics: Four Examples for Structural Ceramics, Chap 4
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
54Ceramics: Four Examples for Structural Ceramics, Chap 4
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
55Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
SiC as a Semiconductor
Properties Unit Si AsGa 3C-SiC 4H-SiC 6H-SiC GaN
Lattice
constant 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
56Ceramics: Four Examples for Structural Ceramics, Chap 4
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
57Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
SiC made of Organic Pre-cusors
58Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
SiC Applications
Yaimij, 1976
+1978
59Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Silicon nitride Si3N4
60Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
61Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Si3N4: Structure
Structure of - and -Si3N4
62Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Si3N4: Structure
Structure of - and -Si3N4
(www.hardmaterials.de ,
Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000)
63Ceramics: Four Examples for Structural Ceramics, Chap 4
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
64Ceramics: Four Examples for Structural Ceramics, Chap 4
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
65Ceramics: Four Examples for Structural Ceramics, Chap 4
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
66Ceramics: Four Examples for Structural Ceramics, Chap 4
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
67Ceramics: Four Examples for Structural Ceramics, Chap 4
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
68Ceramics: Four Examples for Structural Ceramics, Chap 4
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
69Ceramics: Four Examples for Structural Ceramics, Chap 4
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
70Ceramics: Four Examples for Structural Ceramics, Chap 4
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!
71Ceramics: Four Examples for Structural Ceramics, Chap 4
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
72Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
The SiAlBeONe = Mixed Crystalls (solid solutions) of Si3N4
73Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
74Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
75Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
76Ceramics: Four Examples for Structural Ceramics, Chap 4
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
77Ceramics: Four Examples for Structural Ceramics, Chap 4
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
78Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
More Ceramics for Structural Applications
• Boron nitride (BN)
• Boron carbide (B4C)
• Tungsten carbide (WC)
• Carbon (diamond, graphite)
79Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
80Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
“Hardmetal” WC/Co
Tungsten carbide grains (90-94%) in a Cobalt matrix (6-10%)
81Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Comparison: Ceramic – Metal - Polymer
82Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Summary
83Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Summary
84Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Additional Slides
85Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Properties of Non-Oxide Materials
86Ceramics: Four Examples for Structural Ceramics, Chap 4
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
(%
)
87Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Resistivity as Function of the Temperature (hex BN)
88Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Aluminium Melting
Electrical current
supply
Alumina
Cryolite
Carbon anodes
Alumina
Crust
fluidicAlumina
Carbon cathode
Melt: 950 °C
89Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Bayer Prozess
90Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Strength distribution within Production Batches
Strength
Metal
Ceramic
Fre
quen
cy
K, M - average value of the strength
91Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Zincblende structure: ZnS
92Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I
Phase diagram of the Si-C – System
93Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
94Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
95Ceramics: Four Examples for Structural Ceramics, Chap 4
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
(from: http://www.keramverband.de/brevier_engl)
96Ceramics: Four Examples for Structural Ceramics, Chap 4
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
(from: http://www.keramverband.de/brevier_engl)
97Ceramics: Four Examples for Structural Ceramics, Chap 4
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
(from: http://www.keramverband.de/brevier_engl)
98Ceramics: Four Examples for Structural Ceramics, Chap 4
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)
99Ceramics: Four Examples for Structural Ceramics, Chap 4
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
(from: http://www.keramverband.de/brevier_engl)
100Ceramics: Four Examples for Structural Ceramics, Chap 4
Material Science I