Transcript Selection of ceramics

Lesson 6
2014
Lesson 6
2014
 Our goal is, that after this lesson, students
are able to recognize the key criteria for
selecting ceramics and are able to use this
knowledge to support the systematic
material selection process.
What are ceramics for engineering
applications?
?
Typical ceramics used in engineering applications
 Aluminium oxide (Alumina) Al2O3
 Aluminium nitride AlN
 Silicon carbide SiC
 Silicon nitride Si3N4
 SiAlON (Si-Al-O-N)
 Zirconium oxide (Zirconia) ZrO2
 Boron carbide B4C
 Boron nitride BN
Some general properties of ceramics
 Density
 In general the density of ceramics is between metals and
polymers.
 Most light weight ceramics are Boron compounds and Silicon
compounds.
 For ceramics two types of density values are used:
 Density to describe weight
 Density to discribe the functional porosity (e.g. in filters
porosity could be 40-80% of total volume)
 Functional density can be tuned according to requirements.
 Melting point
 The melting point of ceramics is remarkably higher
compared to metals.
 Heat conductivity
 Heat conductivity of ceramics is between metals and
polymers.
 Can be tuned according to requirements.
 Heat expansion
 Depends a lot about the compound.
 Can be tuned according to requirements.
 Modulus of elasticity
 The modulus of elasticity is near or above the values of
metals.
 Modulus of elasticity can be tuned by utilizing composite
compounds:



E.g. WC+Co: E= 600GN/ mm2,
Al2O3+SiO2-particles added + Al: E= 200 GN/mm2
Al: E=70 GN/mm2
 Strength
 Brittle behaviour is typical for ceramics.
 Instead of yeld strength only ultimate
tensile/compression strengths are given.
 Compression strength is even 10-times higher than
tensile strength.
 Porosity affects greatly the strength.
 Ceramics have higher strength in extreme (high)
temperatures compared to metals, but due to so-called
“glass deformation phase” also the strength of ceramics
usually decreases in elevated temperatures (could be
avoided with reaction sintering).
 Hardness
 The highest values of hardness are found among the
ceramics (Boron compounds).
 High hardness remains also in high temperatures (even
at 1000 °C).
 The final hardness is achieved during the sintering
process.
 Electrical properties
 Ceramics can function as electric insulators (the most
typical option), semi-conductors , conductors or even
superconducters
 Also piezo-electric properties can be produced
 Some ceramics are good electric insulators and have
also good heat and corrosion resistance.
 Magnetic properties
 Possible to produce permanent magnets.
PROPETIES OF THE
RAW MATERIAL
PROPETIES OF THE
COMPOUND
POROSITY
LEVEL OF
PURITY
ALLOYING
DUCTILITY EFFECT
(ZIRCONIUM)
DIRECTION OF
COMPRESSION
DETAILED
SELECTION OF
CERAMICS
ASPECTS OF THE
POWDER
METALLURGICAL
PROCESS
GRAIN SIZE
SINTERING
METHOD
POWDER METALLURGIC MANUFACTURING PROCESS
MANUFACTURE OF THE
MOLD AND THE
COMPRESSION TOOLS
ATOMIZATION
MANUFACTURING
(GRINDING) PROCESSES OF
THE POWDER
REDUCTION
PROCESSES
ELECTROLYSIS
MIXING PROCESSES OF THE
POWDER
MgO, CeO2, Al2O3, SiO2,
Y2O3, ZrO2, CaO, MoSi2
SHAPING OF THE POWDER
SINTERING PROCESS
FINISHING PROCESSES
Pressureless sintering
Nitride bonding
Reaction bonding
Liquid-phase sintering
Recrystallization
Hot isostatic pressing
Hot pressing
 During the properly made systematic
material selection process it is necessary to
recognize::
 Limitations and possibilities of powder
metallurgical manufacturing process
 Guidelines of designing the suitable
geometry of the product for the powder
metallurgical manufacturing process
 The optional materials (typically
constructional ceramics) which can be
applied to powder metallurgical
manufacturing process
Density
Temperature T
Pressure p
Compression pressure
Time t
The most important process parameters in powder metallurgical process
OPTIONAL MANUFACTURING TECHNOLOGY 1
Component made of Silicon carbide and nitride
with Gelcasting.
OPTIONAL MANUFACTURING TECHNOLOGY 2
Laser beam
Motion path of the sintering
laser beam
Powder layer to be sintered
Product made of sintered
powder layers
Utilized space for powder mass
Example of expressing the purity grade
How alloying affects the bending strength?
Ceramics
(alloying)
Bending
strength
(N/mm²)
Al2O3
350-380
Al2O3 + ZrO2
350-550
ZrO2 + MgO
650-800
ZrO2 + Y2O3
1000-1500
HEAT CONDUCTIVITY [W/mK]
EFFECT OF ALLOYING ON HEAT CONDUCTIVITY
SiC (BeO alloying)
SiC (B4C alloying)
TEMPERATURE [°C]
How alloying affects the modulus of elasticity?
Ceramics
E
[GPa]
Hot pressed silicon nitride
Alloying with 8% Y2O3
Alloying with 1% MgO
Alloying with 10% CeO2
335
325
327
Alloying with 4% Y2O3 + 3% Al2O3
305
Alloying with 4% Y2O3 + SiO2
305
10% improvement
How Zirconium oxide (ZrO2) alloying affects the mechanical
properties of other ceramic compounds?
 Zirconium oxide itself suffers from unbalanced change
of length and volume expansion between the
tetragonal and monoclinic phase. This causes huge
internal stresses and pure Zirconium oxide can not be
used for constructional purposes.
 The phase change can be fully stabilized by Calcium
oxide (CaO) alloying, but the strength and heat
resistance properties will be so poor that neither the
fully stabilized Zirconium oxide can’t be used in
mechanical constructions.
POLYMORPHISM OF ZIRCONIUM OXIDE
CRYSTAL STRUCTURE
3000
MOLTEN
TEMPERATURE [°C]
2500
CUBIC PHASE
2000
1500
TETRAGONAL PHASE
1000
500
0
MONOCLINIC PHASE
 Partially stabilized Zirconium oxide (PSZ =Partially
Stabilized Zirkonia) can be manufactured by alloying
Yttrium oxide (Y2O3) or cerium oxide (CeO2). This
decreases the risk of failure due to internal stresses
and increases the strength and ductility.
 Partially stabilized Zirconium oxide can be
utilized as an alloying component in other
ceramic compounds to improve their ductility (e.g
Zirkonia Toughened Alumina, ZTA).
Tuning options of the grain size
Different powder particles
(Compound)
Different sizes
Same powder particles
Different sizes mixed
Same powder particles
Optional (same) sizes selected
How grain size affects strength and modulus of elasticity?
Strength
Grain size
Grain size
Grain size
ratio
Density
Modulus of
elasticity
MPa
min μm
max μm
max/min
g/cm³
GPa
General Electric β-SiC
439
0,5-2
100
50 - 200
3,04
376
Carborundum α-SiC
325
2-5
15-18
3–9
3,09
428
Kyocera α-SiC
386
1,5-5
10
2–7
3,14
403
Ceramics
(commercial grades)
Sintered Silicon carbide
When the grain size ratio decreases, the strength decreases and the
modulus of elasticity increases. However, the selected sintering
process gives a new viewpoint to this conclusion!
Same powder particles
Different sizes mixed
STRENGTH OF SILICON CARBIDES / GRAIN SIZE
MPa
Same powder particles
Optional (same) sizes selected
Note!
Smaller grain
size referres
to higher
strength
STRENGTH
Note!
Selected sintering
process affects
together with the
grain size!
MODULUS OF ELASTICITY OF SILICON CARBIDES / GRAIN SIZE
GPa
Same powder particles
Optional (same) sizes selected
Note!
Smaller grain
size referres
to lower
modulus of
elasticity
MODULUS OF
ELASTICITY
Note!
Selected sintering
process affects
together with the
grain size!
Powder metallurgy/Focus of review articles
Cost effectiveness
Ceramic materials
Steel
Injection molding
Compaction
Microstructure
Metallurgy
Powder metals
Sintering
Powder metallurgy
0
20
40
60
80
100
120
140
160
180
200
What happens during the compression and sintering?
Changes of the grain structure due to sintering and compression.
 Examples of the overall shrinkage of some ceramics
during the powder metallurgical manufacturing
process.
Ceramics
Shrinkage %
Silicon carbide
18-20
Aluminium oxide
17-20
Zirconium oxide
25-32
SINTERING PROCESSES / SILICON CARBIDE
SSIC
(Pressure sintered)
SSIC
(Pressureless sintered)
HPSIC
(Hot pressed)
NSIC
(Nitride bonded)
RSSIC
(Reaction-bonded)
SILICON
CARBIDE
SiC
HIPSIC
(Hot isostatic pressed)
LPSIC
(Liquid-phase sintered)
RCSIC
(Recrystallized)
SINTERING PROCESSES / SILICON NITRIDE
SSN
(Pressure sintered)
RBSN
(Reaction-bonded)
SILICON
NITRIDE
Si3N4
HIPSN
(Hot isostatic pressed)
HPSN (Hot pressed)
Examples of typical sintering temperatures
Ceramics
Al2O3
Sintering
temperature
[°C]
1800
SiC
2500
Si3N4
1700
How sintering process affects bending strength?
Ceramics and
sintering process
Bending strength
(N/mm²)
Reaction sintered
SiC
200-450
Sintered
SiC
350-550
Reaction sintered
Si3N4
200-400
Sintered
Si3N4
500-750
Note!
If reaction sintering
is used, the strength
of ceramics will NOT
decrease in elevated
temperatures!
How sintering process affects modulus of elasticity?
Ceramics and
Sintering process
Modulus
of
elasticity
GPa
Hot pressed
Silicon carbide
450
Sintered
Silicon carbide
400
Reaction sintered
Silicon Carbide
360
How sintering process affects hardness of ceramics?
Sintering process
of Silicon nitride
Hardness
Pressure sintered
1400-1800 HV
Hot pressed
1500-1800 HV
Reaction bonded
400-700 HV
STRENGTH OF SILICON CARBIDES / SINTERING PROCESSES
MPa
STRENGTH
Note!
Selected sintering
process affects
together with the
grain size!
MODULUS OF ELASTICITY OF SILICON CARBIDES /
SINTERING PROCESSES
GPa
MODULUS OF
ELASTICITY
Note!
Selected sintering
process affects
together with the
grain size!
COMPRESSION STRENGTH / COMPRESSION DIRECTION
Note!
Bonding reaction
affects together
with the
compression
angle!
BENDING STRENGTH / COMPRESSION DIRECTION
Note!
Bonding reaction
affects together
with the
compression
angle!
THERMAL EXPANDING / COMPRESSION DIRECTION
10
8
6
4
Boron oxidation
Calsium carbonate
Perpendicular
Parallel
Perpendicular
Note!
Bonding reaction
affects together
with the
compression
angle!
Parallel
0
Perpendicular
2
Parallel
THERMAL EXPANDING [10-6/°C]
12
Diffusion
BONDING REACTION AND LOAD DIRECTION RELATED
TO THE COMPRESSION ANGLE
Strength!
Compression
angle
BO, CA, XP!
Heat
resistance!
Justification of ceramic applications
Ceramics
The most important property for industrial applications
ALUMINIUM OXIDES
Cost-effectiveness compared to other ceramics with Good
chemical resistance.
ALUMINIUM NITRIDES
Excellent thermal conductor but at the same time excellent
electric insulator.
SILICON CARBIDES
Good heat resistance.
SILICON NITRIDES
Good heat resistance combined with excellent resistance
against heat shocks.
Si-Al-O-N
Mechanical properties close Silicon nitride combined with
chemical resistance close to properties of Aluminium oxide.
(one type of silicon nittide)
ZIRCONIUM OXIDE
Could be utilized to improve the toughness/ ductility of other
ceramic materials. Use in oxygen sensors.
BORON CARBIDE
Extremely hard (place 4. in the list of constructional materials)
BORON NITRIDE
Extremely hard (place 3. in the list of constructional materials)
Applications of Aluminium oxide
 A ball valve made of
aluminium oxide.
Applications of Aluminium nitride
Aluminium nitride is used in waveguide amplifiers and
angular waveguides (MW-mechanics or high power
electronics applications).
Applications of Silicon carbide
Turbine (blades) made of Silicon carbide
Chemically resistant seals made of Silicon carbide
Applications of Silicon nitride
Applications of Si-Al-O-N
Si-Al-O-N based cutting tools
Si-Al-O-N based seals and sliding bearings
Applications of Zirconium oxide





Ceramic foam filters
Unit porosity(percentage ): 80…90 %
Density (g /cm3): 1.0
Approximate use temperature 1700 °C.
Thermal shock resistance: in 1110° C above 7 times
 Ceramic Zirconia based oxygen sensors
Applications of Boron Carbide
Applications of Silicon nitride
 The boron-nitride coatings combine the
strength and durability with the lubrication and
anti-frictional properties e.g. of pistons and
cylinders in an engine.
FOUR-FIELD ANALYSIS FOR MECHANICAL/ELECTRICAL ENGINEERING
HARDNESS
ELECTRICAL
OR
HEAT
CONDUCTIVITY
(COMPRESSION)
STRENGTH
HEAT RESISTANCE
FOUR-FIELD ANALYSIS FOR PROCESS ENGINEERING
HEAT RESISTANCE
FUNCTIONAL
POROSITY
CHEMICAL
STABILITY
COSTS
How to name properly the selected
ceramics?
Hot pressed
Silicon carbides
 In addition to the ceramics type (e.g. Al2O3,
SiC…) the following data is required:
 Purity level [%]
 Alloying [%], at least Zirconium content if it




used
Grain size [either grain size ratio or grain size
limit]
Porosity level [vol-% and/or density]
Sintering method [HPSN, RSSC…]
Direction of compression
 Remember the ”problems” with commercial
names of different grades
Norton NC-203
Ceradyne 146A
Ceradyne 146I
Sintered
Silicon carbides
General Electric βSiC
Carborundum α-SiC
Kyocera α-SiC
Reaction sintered
Silicon carbides
Norton NC-435
Norton NC-430
UKAEA BNF Refel
Coors SC-1