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Ceramic Structural Composites The Most Advanced
Structural Material
Lance L Snead Presented at the International
School on Fusion Reactor Technology Erice,
Italy July 26 - August 1, 2004
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Composite -v- Monolithic Ceramics
Interphase
LOAD
matrix
fiber
crack
crack arrest
Fiber
Composite materials, whether platelet, chopped
fiber, or continuous fiber reinforced are
superior engineeringmaterials to monolithics
generally higher strength, especially in
tension higher Weibull modulus (more
uniform failure) much higher damage
tolerance (fracture toughness)
Matrix
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Composite -v- Monolithic Ceramics
Toughness MPa/m-1/2
Steel gt50
Monolithic Ceramic 3
Platelet Reinforced Ceramic 6
Chopped Fiber Reinforced 10
Continuous Fiber Reinforced Ceramic 25-30
Monolithic Strength (MPa) Composite Strength (MPa)
SiC 100 50 220 20
Graphite 107 20 176 20
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Ceramic Structural Composites The Most Advanced
Structural Material
Composite Examples
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Structural Composites in Aerospace Applications

• Thermal protection system for a re-entry space
  vehicle Nose corn, leading edge,
• Rocket engine Extendable nozzle, aerospike
  engine,
• Scram-jet engine for a future space vehicle.

C/C with TBC/EBC is in commercial. SiC/SiC will
be more attractive (e.g. Tyrannohex).
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Exhaust Tail-cone
Weaving / 2D Cloth
Stitching Successfully engine demonstrated at
gas temperature 1573K (1998)
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SiC/SiC Thrust chamber
Weaving /
3-Axial Braiding Successfully hot firing
tested at gas temperature 2073K (1998)
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Carbon Fiber Reinforced Composites
TREK Madone 5.9 Carbon Fiber Composite
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Glass Fiber Reinforced Composites
Ferrari 308 GT4 Glass Fiber Composite
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Reinforced Concrete Composite
Steel reinforced rebar Carbon
Fiber/epoxy rod
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Reinforced Fired Adobe Composite
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Reinforced Fired Adobe Composite
Present Day
Inca city 1500 AD
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Reinforced Fired Adobe Composite
Present Day
Inca city 1500 AD
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Puye Cliff Dwelling Anasaze Indians 1100-1580 AD
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Fort Paramonga Chimu civilization 1300 AD
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Tel-Dan Arch 1600 BC
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Short History of Materials
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Ceramic Structural Composites The Most Advanced
Structural Material
Fusion Structural Composites
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Yield Strength of Various Structural Materials
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Operating Range, Highly Irradiated Structural
Materials
Questionable
Reasonable
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Ceramic Structural Composites The Most Advanced
Structural Material
Carbon/Carbon Composites - In widespread
structural use - Manufacturing and design
methods understood - Expensive
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Divertor Designs Using C/C Composites
Full-scale vertical target armored mock-up uses a
pure Cu clad DS-Cu tube armored with saddle-block
C/C and CVD-W armors. (Hitachi Ltd., Japan)
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Pure Cu clad DS-Cu tube armored with C/C
monoblocks. (Kawasaki Heavy Industries, Japan)
C/C
C/C
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Ceramic Structural Composites The Most Advanced
Structural Material
Irradiation Performance of Carbon Fiber
Composites
- Lifetime is limited - Tritium Retention
Unavoidable
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Graphite Under Irradiation
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CFCs Under Irradiation
(HFIR , 600C)
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Composite allows engineering ofproperties
such as dimensional change
CFCs Under Irradiation
fiber
gap
10 dpa
500C
800C
sample surface
bundle swelling
bundle shrinkage
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gap
bundle swelling
bundle shrinkage
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T-3 attaches to basal plane edges and highly
defected structure. More perfect material
and/or high temperature allows less retention.
NRL IFE 2/2001
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Ceramic Structural Composites The Most Advanced
Structural Material
SiC/SiC Composites - Essentially no current
structural application - Manufacturing and
design methods immature
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ARIES-I First Blanket Design Using SiC/SiC

• Excellent safety environmental characteristics
  (very low activation and very low afterheat).
• High performance due to high strength at high
  temperatures (gt1000ºC).

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ARIES-AT Liquid Wall Blanket Concept (USA)

• Simple, low pressure design with SiC structure
  and self-cooled Pb-17Li breeder.
• High Pb-17Li outlet temperature (1100ºC) and
  high thermal efficiency of 58.5.
• - Max SiC/SiC temp. 996ºC.
• - Max SiC/SiC-coolant (Pb-17Li) interface temp.
  900-940ºC.
• Simple manufacturing technique.
• Very low afterheat.
• Class C waste by a wide margin.

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TAURO SiC/SiC Blanket Design in EU

• Self-cooled Pb-17Li breeder and n multiplier.
• Pb-17Li inlet/outlet temperature (650/860ºC).
• - Max SiC/SiC temp. 995ºC.
• - Max SiC/SiC-coolant (Pb-17Li) interface temp.
  915ºC.
• Simple manufacturing technique (based on joining
  of panels/tubes by brazing).
• The maximum shear in the joints is 60MPa.
• 6mm thickness as first wall to deal with
  thermo-mechanical loads.
• Brayton cycle thermal efficiency gt47.

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Ceramic Structural Composites The Most Advanced
Structural Material
SiC/SiC Composites Under Irradiation - May
survive for life of machine - Thermal
conductivity is likely less than assumed -
Electrical conductivity appears not to be a
problem
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SiC Under Irradiation
Irradiation-induced thermo-physical property
changes (swelling, thermal conductivity,
strength) saturate by a few dpa for Tlt 1000C.
Driven by simple defect clusters. Irradiation
performance for Tgt1000C is not well understood.
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Silicon Carbide Under Irradiation
Irradiation-induced thermo-physical property
changes (swelling, thermal conductivity,
strength) saturate by a few dpa for Tlt 1000C.
Driven by simple defect clusters. Irradiation
performance for Tgt1000C is not well understood.
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SiC/SiC Composites Strength and Stability
Until recently, SiC/SiC composites exhibited
significant degradation in mechanical properties
due to non-SiC impurities in fibers causing
interfacial debonding.
Bulk SiC
SiC-interlayer
Thin C-interlayer
SiC-interlayer
Ceramic fiber
0.5 ?m
SiC multilayers
SiC fiber
300 nm
Upon irradiation, if fibers densify,
fiber/matrix interfaces debonds --gtstrength
degrades
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SiC/SiC Composites Strength and Stability
Bend strength of irradiated advanced composites
show no degradation up to 10 dpa
1st- and 2nd generation irradiated SiC/SiC
composites show large strength loss after doses
gt1 dpa
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SiC/SiC Composites Thermal Conductivity
CVD SiC Irradiated
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SiC/SiC Composites Thermal Conductivity
radiation defects
intrinsic defects
boundaries
umklapp
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SiC/SiC Composites Thermal Conductivity
Data for an ideal SiC Thermal conductivity
reduction is due to simple vacancies and vacancy
clusters. This is a strict material property
which can not be improved upon.
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SiC/SiC Composites Thermal Conductivity
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SiC/SiC Composites Thermal Conductivity
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SiC/SiC Composites Thermal Conductivity
Due to interfaces and cracks in SiC composite,
thermal conductiivity will necessarily be less
than ideal SiC. Present materials are
significanlty lower than 15 W/m-K reactor study
goal.
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Composite Comparison for FISSION (at 1000C)
does not include prototyping or NDE
evaluation.
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Ceramic Structural Composites The Most Advanced
Structural Material
SiC Matrix / Graphite Fiber Composites - Now
being used in NASA application - Manufacturing
and design methods immature - May solve the
dual problems of low thermal conductivity of
SiC/SiC and high T-3 retention of C/C
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Argument 1 Strength ( toughness) as good or
superior to SiC/SiC

Tensile Strength (MPa)
SiC/SiC Composite (2-D lay-up)
SiC/graphite Composite (2-D lay-up)
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Argument 2 Reduced tritium retention over best
C/Cs
Tirr600C Tload1000C
Tritium retention, non-irradiated and irradiated,
is highly dependent on graphite perfection.
K-1100 type fibers are nearly perfect. SiC
has very low tritium retention.
Reduced Basal Plane Edge
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Argument 2 Reduced tritium retention over best
CFCs
Intermediate Quality Graphite
By replacing the lower perfection matrix of
CFCs with SiC, SiC/graphite will have lower
retention.
High Quality Graphite Fiber Composite
Tirr200C Tload1000C
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Argument 3 Significant thermal conductivity
enhancement
Defect Resistance
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Engineered High Thermal Conductivity SiC/G
Composite
Matrix CVI SiC , no interphase Fibers
Z-direction either Amoco P55
or Thornel K-1100 fiber X-Y
direction Amoco P-55 fiber.
Total Volume Fraction 44. Architecture
Unbalanced 1-1-6 weave.

High TC
K1100 fiber
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SiC Matrix / Graphite Fiber Composites
At fusion-relevant temp., SiC/g --gt
conductivity exceeds present SiC/SiC --gt
conductivity exceeds SiC theoretical max. --gt Low
TC direction on order of SiC/SiC thermal
conductivity (for this composite).
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SiC Matrix / Graphite Fiber Composites
At fusion-relevant temperature, SiC/g
exceeds theoretical maximum of SiC/SiC
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Summary
Fiber reinforced composites are arguably the
oldest man-made structural material. However,
because predictive design tool (codes) have been
based on metallic design over the past century
structural design with composites is currently
impractical. Design is based on prototyping, not
modeling. Carbon fiber composite
manufacturing and application is fairly mature,
however lifetime of composite structures is
strictly defined to 15 dpa, or a year in a
fusion reactor. Tritium retention in CFCs can
be reduced, but never eliminated. SiC/SiC
composite offer the possibility of lifetime
components, but as-irradiated thermal
conductivity will almost certainly be less than
the 15 W/m-K assumed in present studies.
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Questions ???
Questions ?
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Fabrication of C/C Composites

• Carbon Fiber
• PAN (polyacrylonitrile) based carbon fiber
• Commercial use for general purpose.
• Varieties high strength, high modulus, long
  elongation,
• Pitch based carbon fiber
• High performance carbon fiber Anisotropic, high
  graphitization.
• Tensile strength 2.34.0GPa, Tensile modulus
  400900GPa
• General purpose (low cost) carbon fiber
  Isotropic microstructure.
• Tensile strength 0.61.0GPa, Tensile modulus
  3060GPa
• Carbon Matrix
• Chemical vapor deposition (CVD)
• Impregnation and pyrolysis using resin or pitch.
• Environmental Barrier Coating
• Concern about high reactivity to
• oxidative products.
• Boron based glasses (lt1000ºC)
• Silicon carbide (lt1500ºC)

carbon
Temperature
graphite
Graphitization
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Key Characteristics of SiC(-based) Fibers