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

Matrix Fiber Interphase Composite -v- Monolithic Ceramics fiber matrix crack arrest LOAD Composite materials, whether platelet, chopped fiber, or continuous fiber reinforced are superior “engineering”materials to monolithics: generally higher strength, especially in tension higher Weibull modulus (more uniform failure) much higher damage tolerance (fracture toughness)

Monolithic Strength (MPa) Composite Strength (MPa) SiC100 ± ± 20 Graphite107 ± ± 20 Composite -v- Monolithic Ceramics Toughness MPa/m -1/2 Steel>50 Monolithic Ceramic3 Platelet Reinforced Ceramic6 Chopped Fiber Reinforced10 Continuous Fiber Reinforced Ceramic 25-30

Ceramic Structural Composites The Most Advanced Structural Material Composite Examples

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).

Weaving / 2D Cloth + Stitching Successfully engine demonstrated at gas temperature 1573K (1998) Exhaust Tail-cone

Weaving / 3-Axial Braiding Successfully hot firing tested at gas temperature 2073K (1998) SiC/SiC Thrust chamber

Carbon Fiber Reinforced Composites TREK Madone 5.9 Carbon Fiber Composite

Glass Fiber Reinforced Composites Ferrari 308 GT4 Glass Fiber Composite

Reinforced Concrete Composite Steel reinforced “rebar” Carbon Fiber/epoxy rod

Reinforced Fired Adobe Composite

Inca city ~ 1500 AD Present Day Reinforced Fired Adobe Composite

fiber matrix crack arrest LOAD Inca city ~ 1500 AD Present Day Reinforced Fired Adobe Composite

Puye Cliff Dwelling Anasaze Indians AD

Fort Paramonga Chimu civilization ~1300 AD

Tel-Dan Arch ~1600 BC

10000 bc5000 bc bc5000 bc Date Relative Importance METALS POLYMERS/ ELASTOMER COMPOSITES STRAW-BRICK HORSEHAIR PLASTER GFRE C/C METAL MATRIX CERAMIC MATRIX WOOD SKIN FIBERS GLUES RUBBER BAKELITE NYLON POLYESTERS P.E. EPOXIES PMMA ACRYLICS HIGH MODULUS POLYMERS HIGH TEMPERATURE POLYMERS GOLD COPPER BRONZE IRON CAST IRON STEELS ODS STEELS LIGHT ALLOYS NEW SUPERALLOYS SUPER ALLOYSGLASSY METALS TITANIUM, ZIRCONIUM etc. ALLOYS PYROLITIC CERAMICS TOUGHENED CERAMICS CERAMICS/ GLASSES STONE FLINT POTTERY GLASS CEMENT REFRACTORIES PORTLAND CEMENT FUSED SILICA CERMETS Short History of Materials

Ceramic Structural Composites The Most Advanced Structural Material Fusion Structural Composites

SiC/SiC Yield Strength of Various Structural Materials

C/C SiC/SiC Tungsten Molybdenum ODS Ferritic F/M Steel 316 Stainless Alloy 718 Questionable Reasonable Operating Range, Highly Irradiated Structural Materials

Ceramic Structural Composites The Most Advanced Structural Material Carbon/Carbon Composites - In widespread structural use - Manufacturing and design methods understood - Expensive…

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) Pure Cu clad DS-Cu tube armored with C/C monoblocks. (Kawasaki Heavy Industries, Japan) W C/C

Ceramic Structural Composites The Most Advanced Structural Material Irradiation Performance of Carbon Fiber Composites - Lifetime is limited - Tritium Retention Unavoidable

Graphite Under Irradiation H451 Graphite

CFC’s Under Irradiation (HFIR, 600°C)

Composite allows “engineering” of properties such as dimensional change sample surface bundle shrinkage bundle swelling gap 500°C800°C ~ 10 dpa fiber CFC’s Under Irradiation

bundle shrinkage bundle swelling gap

T-3 Retention (appm) Irradiation / T-3 Loading Temperature (C) Non-irradiated, infinite charge time Non-Irradiated 1 hr Charge Time High Quality Irradiated CFC (Causey, Snead) Intermediate Quality Irradiated Graphite (Causey, Snead) NRL IFE 2/2001 T-3 attaches to basal plane edges and highly defected structure. More perfect material and/or high temperature allows less retention. CFC’s Under Irradiation : Tritium Retention

Ceramic Structural Composites The Most Advanced Structural Material SiC/SiC Composites - Essentially no current structural application - Manufacturing and design methods immature

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 (>1000ºC).

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.: ºC. Simple manufacturing technique. Very low afterheat. Class C waste by a wide margin.

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: >47%.

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

SiC Under Irradiation Irradiation-induced thermo-physical property changes (swelling, thermal conductivity, strength) saturate by a few dpa for T< 1000°C. Driven by simple defect clusters. Irradiation performance for T>1000°C is not well understood.

Silicon Carbide Under Irradiation Irradiation-induced thermo-physical property changes (swelling, thermal conductivity, strength) saturate by a few dpa for T< 1000°C. Driven by simple defect clusters. Irradiation performance for T>1000°C is not well understood.

SiC/SiC Composites : Strength and Stability Ceramic fiber 0.5  m SiC-interlayer Thin C-interlayer SiC-interlayer Bulk SiC Until recently, SiC/SiC composites exhibited significant degradation in mechanical properties due to non-SiC impurities in fibers causing interfacial debonding. Upon irradiation, if fibers densify, fiber/matrix interfaces debonds -->strength degrades 300 nm SiC fiber SiC multilayers

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 >1 dpa

SiC/SiC Composites : Thermal Conductivity CVD SiC Irradiated

SiC/SiC Composites : Thermal Conductivity umklapp boundaries intrinsic defects radiation defects Thermal Defect Resistance Umklapp

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.

SiC/SiC Composites : Thermal Conductivity Umklapp (phonon Scattering) boundaries intrinsic defects radiation defects

SiC/SiC Composites : Thermal Conductivity Umklapp (phonon Scattering) boundaries intrinsic defects radiation defects x=goal

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. SiC/SiC Composites : Thermal Conductivity

* does not include prototyping or NDE evaluation. Composite Comparison for FISSION (at 1000°C)

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

Tensile Strength (MPa) SiC/SiC Composite (2-D lay-up) SiC/graphite Composite (2-D lay-up) Argument #1: Strength (& toughness) as good or superior to SiC/SiC

Argument #2: Reduced tritium retention over best C/C’s T irr =600°C Tload=1000°C Reduced Basal Plane Edge 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.

Argument #2: Reduced tritium retention over best CFC’s By replacing the lower perfection matrix of CFC’s with SiC, SiC/graphite will have lower retention. T irr =200°C Tload=1000°C Intermediate Quality Graphite High Quality Graphite Fiber Composite

Argument #3: Significant thermal conductivity enhancement Defect Resistance

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 weave. K1100 fiber High TC

SiC Matrix / Graphite Fiber Composites At fusion-relevant temp., SiC/g: --> conductivity exceeds present SiC/SiC --> conductivity exceeds SiC theoretical max. --> Low TC direction on order of SiC/SiC thermal conductivity (for this composite).

At fusion-relevant temperature, SiC/g exceeds theoretical maximum of SiC/SiC SiC Matrix / Graphite Fiber Composites

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 CFC’s 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.

Questions ? Questions ???

Fabrication of C/C Composites “Graphitization” carbon graphite Temperature 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: 2.3~4.0GPa, Tensile modulus: 400~900GPa -General purpose (low cost) carbon fiber: Isotropic microstructure. Tensile strength: 0.6~1.0GPa, Tensile modulus: 30~60GPa 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 (<1000ºC) Silicon carbide (<1500ºC)

Key Characteristics of SiC(-based) Fibers