Ceramics: Four Examples for Structural Ceramics, Chap 4. Material Science I.
Ceramic Materials. F. Filser & L.J. Gauckler. ETH-Zürich, Departement Materials.
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
3
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
6
Material Science I
Aluminiumoxid - Al2O3 (Alumina)
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
9
Material Science I
-Al2O3: Structure
Ceramics: Four Examples for Structural Ceramics, Chap 4
10
Material Science I
Bauxite Resources on Earth
oxygen silicon aluminium iron magnesium copper zinc tin
Ceramics: Four Examples for Structural Ceramics, Chap 4
11
Material Science I
Bauxite Resources on Earth
Ceramics: Four Examples for Structural Ceramics, Chap 4
12
Material Science I
Aluminium Production Process Aluminium metal (fluid)
precipitator anode crushing mill
agitator
calcining furnace
filter press
digestor cathode
Bauxite
Alumina
Ceramics: Four Examples for Structural Ceramics, Chap 4
Aluminium Melting
Aluminium
Bayer Process in detail
13
Material Science I
Al2O3 and Al(OH)3
Transformation Scheme for Al-Hydroxides and Aluminiumoxides Ceramics: Four Examples for Structural Ceramics, Chap 4
14
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
20
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
• • • •
• • • •
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.
22
Material Science I
Zirconoxide ZrO2 (Zirconia)
Ceramics: Four Examples for Structural Ceramics, Chap 4
23
Material Science I
Characteristic Properties: ZrO2 Specific Weight (Density)
Elastic Modulus
Stress Intensity Factor (Toughness)
Bend Strength
Weibull Modulus (Reliability)
E [GPa]
KIC
B [MPa]
m [1]
60-1000
15-25
g cm3
5.89
200
Hardness [HV10]
[10-6K-1]
1300
10
Ceramics: Four Examples for Structural Ceramics, Chap 4
MPa m
6-10 W m K
Melting Temperature [°C]
2
2680
24
Material Science I
Phase Transformations of ZrO2 as function of temperature Melt ↓
2680°C
cubic
↓
2370°C
tetragonal ↓
1170°C
monoclinic
Ceramics: Four Examples for Structural Ceramics, Chap 4
25
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
27
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=bc ===90
monoclinic abca
==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.
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
31
Material Science I
Phase Diagram of the Binary System ZrO2-Y2O3 cubic
tetragonal
monoclinic
Y2O3
Ceramics: Four Examples for Structural Ceramics, Chap 4
32
Material Science I
ZrO2: Partial Stabilized Zirconia
PSZ - tetragonal segregation in a cubic matrix
Ceramics: Four Examples for Structural Ceramics, Chap 4
33
Material Science I
ZrO2: Tetragonal Zirconia Polycrystals
200 nm
SEM image of 3 mol% Y2O3 stabilised TZP
Ceramics: Four Examples for Structural Ceramics, Chap 4
TEM image of 3 mol% Y2O3 stabilised TZP
34
Material Science I
Critcal Nucleus Radius for the tm 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 r2tm
r
G Volume =4/3r3 Gtm 35
Material Science I
Examples of Typical Components
milling balls with a diameter of 50 m to 25 mm
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
37
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
39
Material Science I
Siliconcarbide SiC
Ceramics: Four Examples for Structural Ceramics, Chap 4
40
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
41
Material Science I
SiC: Structure
Cubic structure: Zinc blende
Ceramics: Four Examples for Structural Ceramics, Chap 4
Phase diagram SiC (www.hardmaterials.de , Handbook of Ceramic Material, R. Riedel (Ed.), Wiley-VCH, 2000)
42
Material Science I
Polytypes of SiC
Unit cell of hexagonal Polytypes of SiC: a1=a2=a3
Ceramics: Four Examples for Structural Ceramics, Chap 4
Atomic positions and bondings for the 2H-SiC unit cell.
43
Material Science I
Stacking variants of SiC
Ceramics: Four Examples for Structural Ceramics, Chap 4
44
Material Science I
SiC Processing
SiO2 + C 1SiC + 2CO 1t + 1.4t Mostly production of CO with an additional product SiC!!!!!
Ceramics: Four Examples for Structural Ceramics, Chap 4
45
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
46
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.
Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Weibull Modulus (Reliability)
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
49
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
50
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
51
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
52
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]
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
56
Material Science I
SiC made of Organic Pre-cusors
Ceramics: Four Examples for Structural Ceramics, Chap 4
57
Material Science I
SiC Applications
Yaimij, 1976 +1978
Ceramics: Four Examples for Structural Ceramics, Chap 4
58
Material Science I
Silicon nitride Si3N4
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
61
Material Science I
Si3N4: Structure
Structure of - and -Si3N4
Ceramics: Four Examples for Structural Ceramics, Chap 4
(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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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.
Ceramics: Four Examples for Structural Ceramics, Chap 4
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
68
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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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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!
Ceramics: Four Examples for Structural Ceramics, Chap 4
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The SiAlON‘s of the 1800°C isothermal cross section of the Si3N4-4AlN-2Al2O3-3SiO2 system with the -Si6-xAlxOxN8-x solid solution
Ceramics: Four Examples for Structural Ceramics, Chap 4
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The SiAlBeONe = Mixed Crystalls (solid solutions) of Si3N4
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Seeds for Controlling the Microstructure
with seeds
with seeds
without seeds
without seeds
Ceramics: Four Examples for Structural Ceramics, Chap 4
-> 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.
Ceramics: Four Examples for Structural Ceramics, Chap 4
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-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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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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Comparison of the - Si3N4 Materials Properties
RBSN
SSN
HPSN
Si+N2Si3N4+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
Ceramics: Four Examples for Structural Ceramics, Chap 4
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More Ceramics for Structural Applications
• Boron nitride (BN)
• Boron carbide (B4C) • Tungsten carbide (WC) • Carbon (diamond, graphite)
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Hardness as Function of the Temperature
Hardness (HV)
Diamond (CC) Cubic Boron Nitride (BNC) (Tetra-) Boron carbide (B4C) Corundum (Al2O3)
1 / Temperature (°C-1)
Ceramics: Four Examples for Structural Ceramics, Chap 4
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“Hardmetal” WC/Co
Tungsten carbide grains (90-94%) in a Cobalt matrix (6-10%)
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Comparison: Ceramic – Metal - Polymer
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Summary
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Summary
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Additional Slides
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Properties of Non-Oxide Materials
Ceramics: Four Examples for Structural Ceramics, Chap 4
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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
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Resistivity as Function of the Temperature (hex BN)
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Material Science I
Aluminium Melting
Carbon anodes
Alumina Cryolite
Alumina Crust
Melt: 950 °C fluidicAlumina Carbon cathode
Electrical current supply
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Bayer Prozess
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Strength distribution within Production Batches
K, M - average value of the strength
Frequency
Metal
Ceramic
Strength
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Zincblende structure: ZnS
Ceramics: Four Examples for Structural Ceramics, Chap 4
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Phase diagram of the Si-C – System
Ceramics: Four Examples for Structural Ceramics, Chap 4
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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)
Ceramics: Four Examples for Structural Ceramics, Chap 4
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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
Ceramics: Four Examples for Structural Ceramics, Chap 4
(from: http://www.keramverband.de/brevier_engl)
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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
(from: http://www.keramverband.de/brevier_engl)
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(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
(from: http://www.keramverband.de/brevier_engl)
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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
(from: http://www.keramverband.de/brevier_engl)
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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
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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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Ceramics: Four Examples for Structural Ceramics, Chap 4
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