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SiC/SiC properties and FCI design

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Hyper-Therm High-Temperature Composites, Inc. SiC/SiC Composite Properties and Flow Channel Insert Design R.J. Shinavski Hyper-Therm HTC Huntington Beach, CA 714-375-4085 [email protected] FNST Meeting UCLA, Los Angeles, CA August 18, 2009
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Page 1: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

SiC/SiC Composite Properties and Flow Channel Insert Design

R.J. ShinavskiHyper-Therm HTC

Huntington Beach, CA

714-375-4085

[email protected]

FNST MeetingUCLA, Los Angeles, CA

August 18, 2009

Page 2: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Introduction• SiC fiber-reinforced silicon carbide matrix (SiC/SiC) composites

combine the attributes of high temperature mechanical strength and toughness with relative dimensional stability under high neutronfluence that address the primary requirement of survivability as a flowchannel insert to isolate the molten Pb-Li from the steel structure

• Properties of Nuclear Grade SiC/SiC are being measured to provide preliminary guidance in assessing viability of design approaches for a SiC/SiC FCI

• Finite element analysis of several FCI design approaches provides insight into the magnitudes of the critical parameters

• Advantages and disadvantages of possible designs for a Nuclear Grade SiC/SiC flow channel insert will be discussed with respect to mechanical, thermal, and electrical properties

• Support technologies being examined such as potential joining/bonding methods will also be discussed

Page 3: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

SiC/SiC Composites

• Hi-Nicalon Type S fiber selected due to greater existing database on this fiber showing radiation resistance

90º Fibers

0º Fibers

Hi-Nicalon Type SCVI SiC

MLSiC fiber coating

• SiC matrix produced by isothermal/isobaric CVI

• Composite bulk densities 2.7 g/cm3

• Fiber coating is Hyper-Therm HTC’s MLSiCfiber coating (US Patents 5,455,106 and 5,480,707)

Page 4: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Mechanical Prop of Nuclear Grade SiC/SiC

24/27 MPa157 MPa0.39%344 MPa---B-basis Allowable*

Mechanical Properties of Nuclear Grade SiC/SiC (5HS)

96 MPa

180 MPaσPL

insufficient data

42/38 MPaσILSS(RT)/σILSS(800C)

---

0.54%εf

------Weibull Analysis**

400 MPa270MeanσfE

* 95% confidence that 90% of the material will be greater than the allowable** Weibull analysis for 1x10-6 failure with calculated Weibull Modulus of 21.1

• Mechanical properties database is being generated for both ambient and elevated temperature properties that consists of tensile stress-strain and interlaminar shear stress

• Tentative design stresses are being established to evaluate the viability of some approaches and to determine the dependency on the design criteria

• Matrix cracking stress as represented by the proportional limit stress is the design limiting mechanical property for in-plane stresses to prevent the possibility of Pb-Li ingress through the SiC/SiC composite

Page 5: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Pb-Li Compatibility• Nuclear grade SiC/SiC has been exposed to Pb-Li at up to 360ºC with

no signs of Pb-Li penetration• Recent experiments conducted with Pb-Li at 475ºC and 100 psi (690

kPa) Ar overpressure were inconclusive as cut specimen edges were insufficiently sealed and allowed LM ingress from the edges

• Such behavior is of concern as FCI segments will likely have cut edges• Experiment is being repeated with greater attention to re-sealing the

edges after machining test specimens• Overpressure has significant impact on wetting of Pb-Li on SiC • Mechanically materials were unchanged

Page 6: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

• In-plane electrical conductivity dominated by small amount of carbon in fiber coating and is not highly sensitive to orientation within the plane

• Data and material show good reproducibility between measurements, samples, and lots of material

• The more critical through thickness electrical conductivity shows a high dependence on the presence/absence of the CVI SiC seal-coat –particularly at lower temperatures

• Need to establish a better understanding of t-t conductivity behavior and measurement due to influence on magnetohydrodynamic effect

Electrical Properties

Testing performed by G. Youngblood at PNNL

Page 7: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Thermal Conductivity

• Through-thickness thermal conductivity of Nuclear Grade SiC/SiC is too high to be a sufficient thermal insulator

• In-plane measurements performed at +/-45 orientation showed at most a 5% difference and thus NG SiC/SiC can likely be considered in-plane isotropic with respect to thermal conductivity

• Architectural design is required to meet the thermal conductivity target of 1-2 W/m/K

• Must measure the “effective” thermal conductivity on the architecturally designed material

Page 8: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Architectural Construction of FCI

• Add thermal conductivities as thermal resistances in series withflutes added in parallel to calculate equivalent “bulk” through thickness thermal conductivity to perform preliminary design

• Examined strut angle and frequency• For lower thermal and electrical conductivity, minimize strut cross-

section and number of struts/unit length• For lower thermal conductivity and a higher electrical conductivity,

maximize the core thickness and minimize the face sheet thickness

Page 9: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Low Thermal Conductivity Construction• Equivalent thermal conductivity

of 1.4 W/m/K is predicted from series-parallel resistance approach

• FEA being performed to refine expected thermal transport

• 1.0 mm face sheets with 0.5 mm thick struts

• 45 degree flute angle maximizes shear strength of truss

• Must determine preferred strut frequency (balance mechanical versus thermal performance)

• Possibility of engineered high compliance in core to mitigate deformation in the composite

5 mm

18 mm

Page 10: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Evaluation of Truss Structure Approach

• Demo articles fabricated with carbon fiber reinforced SiC were produced to establish viability of planned manufacturing approach

• Two truss repeat distances were examined with a constant truss angle of 45 degrees

• Plan to produce using NG SiC/SiC in near term

• Experimentally measure equivalent thermal conductivity using guarded hot plate technique on plates of material

• Test shear strength of structure to determine if core strength or bonding of core to face governs failure

Page 11: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Anticipated Loading of FCI

• Irradiation induced swelling is greater than thermal expansion difference, but thermal expansion changes more rapidly with temperature

• Slot allows free expansion and minimal stresses if unrestrained

• Edges create localized restraints, which result in bending stresses

• Deformation will be asymmetric due to slot

• Use FEA to examine the stress state in the FCI

• First level of complexity is to not consider architectural structure

Page 12: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Finite Element Model of FCI

• Model simply applied a 500-300ºC temperature gradient on the FCI• Deformed shape is magnified 30X (slot deforms more than 2.5 mm out of

plane)• Highest stress (Von Mises) occurs along center line of side opposite slit and

is 86 MPa • Highest principal direction stress 68 MPa• Magnitude of maximum interlaminar shear stress 42 MPa• Predicted interlaminar shear stress is much higher than acceptable

Page 13: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Mechanical Prop of Nuclear Grade SiC/SiC

24/27 MPa157 MPa0.39%344 MPa---B-basis Allowable*

Mechanical Properties of Nuclear Grade SiC/SiC (5HS)

96 MPa

180 MPaσPL

insufficient data

42/38 MPaσILSS(RT)/σILSS(800C)

---

0.54%εf

------Weibull Analysis**

400 MPa270MeanσfE

* 95% confidence that 90% of the material will be greater than the allowable** Weibull analysis for 1x10-6 failure with calculated Weibull Modulus of 21.1

• Mechanical properties database is being generated for both ambient and elevated temperature properties that consists of tensile stress-strain and interlaminar shear stress

• Tentative design stresses are being established to evaluate the viability of some approaches and to determine the dependency on the design criteria

• Matrix cracking stress as represented by the proportional limit stress is the design limiting mechanical property for in-plane stresses to prevent the possibility of Pb-Li ingress through the SiC/SiC composite

Page 14: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Alternate FCI Design

• Closed box section provides greater geometric stability and symmetric deformations

• Assumes only purpose of slot is pressure equalization

• Restraint in closed section reduces stresses

• Again analyze with FEA

Page 15: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Finite Element Modeling Results

• Deformations significantly reduced

• Localized near ends of FCI (deformation scale 300X, instead of 30 X)

• Maximum Von Mises stress reduced to 76 MPa

• Magnitude of maximum interlaminar shear stress 33 MPa

• FCI maintains shape better and is stressed less, but interlaminar shear stress is still likely too high for reliable performance

Page 16: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Nested FCI (nFCI)• Separates electrical and thermal

isolation functionality into two separate sub-components conceived by Smolentsev and Malang (Fusion Science and Technology, July 2009)

• Allows each to be optimized for function• Further reduces stresses as thermal

(outer) FCI can be fabricated from loosely located plates without inducing magnetohydrodynamic losses and minimal temperature drop will be experienced by electrical (inner) FCI

Inner Electrical

FCI

Outer Thermal

FCI

• Currently planning FEA to examine stresses particularly shear stresses in electrical FCI at corners

• Will likely consume several mm more real estate within the duct as thermal insulation target of 1-2 W/m/K cannot be met with less than ~5 mm thickness for the thermal FCI

Page 17: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Joining of SiC/SiC Composites• Anticipated need for strong, tough joints with low activation (stand-

offs, locators, close-outs, multi-piece construction)• Pre-ceramic polymers & solid state displacement reactions (Ti3SiC2)• PNNL has demonstrated joints with strengths of 50 MPa when

produced with an applied pressure of 30 MPa• Pre-ceramic polymer joint strengths of <25 MPa; Pressureless joints

typically <10 MPa• Undertaking an examination of alternate pressureless processing

routes to Ti3SiC2 (MAX phase) formation • Ti3SiC2 selected due to exceptional thermomechanical properties

and thermal shock resistance and low activation composition• Preliminary ion irradiation of MAX phases with 1MeV Kr ions shows

no appreciable damage at up to 12 dpa (Whittle et al, MRS Proceedings 1125 to be published)

Page 18: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

MAX Phase Joining

• Significant additions of SiC filler to better match cte and to distribute residual porosity as very small defects

• Good bonding (can be atomically sharp) between SiC and Ti3SiC2

• Average strengths of in excess of 50 MPahave been obtained

• Strength a strong function of bond thickness for pressureless joining

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Bond Thickness (m)

ILSS

Stre

ngth

(MPa

)

Page 19: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

• Preliminary design data is useful in determining the potential viability of FCI design approaches

• Truss structure design of SiC/SiC thermal insulation allows the thermal properties to be engineered and is predicted to reduce the thermal conductivity by greater than an order of magnitude

• nFCI is currently preferred design approach to minimize shear stresses• Permeability with respect to Pb-Li not as simple as original data indicated

when temperature is increased and overpressure is added• Pressureless joining using MAX phase has been demonstrated

• Continue database accumulation such that tentative design properties can be determined to evaluate potential FCI design approaches

• Additional testing in Pb-Li with overpressure• FEA modeling using architecturally designed truss structure• Directly measure effective through-thickness thermal conductivity of

SiC/SiC engineered fluted core structure• Produce sub-scale FCI and subject to thermal difference that simulates

anticipated strain from combined irradiation and thermal loading

Summary

Planned Work

Page 20: SiC/SiC properties and FCI design

Hyper-Therm High-Temperature Composites, Inc.

Acknowledgment

• We would like to acknowledge Department of Energy – (National Nuclear Security Administration) SBIR Funding under Award Number DE-FG02-07ER84717

• This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.


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