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National Aeronautics and Space Administration

Advanced Woven SiC/SiC Composites for High Temperature Applications Gregory N. Morscher

Ohio Aerospace Institute/NASA Glenn Research Center Cleveland, OH

The temperature, stress, and environmental conditions of many gas turbine, hypersonic, and even nuclear applications make the use of woven SiC/SiC composites an attractive

enabling material system. The development in SiC/SiC composites over the past few years has resulted in significant advances in high temperature performance so that now

these materials are being pursued for several turbine airfoil and reusable

hypersonic applications. The keys to maximizing stress capability and maximizing temperature capability will be outlined for SiC/SiC. These include the type of SiC fiber,

the fiber-architecture, and the matrix processing approach which leads to a variety of matrix compositions and structure. It will also be shown that a range of mechanical,

thermal, and permeability properties can be attained and tailored depending on the needs of an application. Finally, some of the remaining challenges will be discussed in

order for the use of these composite systems to be fully realized. Composites at Lake Louise Canada

(2)

Advanced Woven SiC/SiC Composites for

High Temperature Applications

Gregory N. Morscher, Ohio Aerospace Institute

Special Acknowledgement:

Hee Man Yun, Matech/GSM

James A. DiCarlo and James D. Kiser, NASA Glenn Research Center Ram Bhatt, US Army

Composites at Lake Louise Canada October 28th to November 2nd, 2007

(3)

The Need for High Temperature

Load-Bearing

CMC

Current SOA is Sylramic-iBN

reinforced Melt (Si) -Infiltrated CMC

Æ

NASA N24A

– 1315oC use-temperature for ~ 1000

hours and 100 MPa – would like higher stress capability for turbine components

Higher temperature applications for

advanced turbine and scramjet

engines, TPS structures, leading edge

applications, and even nuclear

applications

prohibit the use of free

matrices with free Si

Therefore, need for

higher stress

capability

(e.g., blades) and

higher

temperature capability

CMC (e.g.,

leading edge and TPS structures)

V a n e 2 / L o t 1 V a n e 2 / L o t 1

Inlet Turbine Vane

(4)

Outline

• The best fiber: Sylramic-iBN for > 1300

o

C

applications

– As the fiber goes, so goes the composite

• Fiber architectures that enable

– Understanding the effect of fiber architecture in

order to fabricate the best combination of

composite properties

• SiC matrices for higher temperatures

– Increasing temperature requirements prohibit free

Si

(5)

Fiber Comparison

1000 hr Use Temperature (σ

f

= 500 MPa)

From, J.A. DiCarlo and H.M. Yun, Handbook of Ceramic Composites, Chapter 2 (Kluwer: NY, 2005)

Oxides

SiC-based

Best of small diameter = Syl-iBN

Sylramic-iBN:

Polycrystalline B-containing SiC fiber (Sylramic, processed by COIC) subjected to post-process nitrogen containing heat treatment at high temperature (> 1700oC). Removes B and improves creep-rupture properties
(6)

Sylramic-iBN Based Composites for Applications > 1300

o

C

Sylramic-iBN = NASA derived heat treatments of Sylramic fiber

Excellent creep resistance and thermal stability (up to 1800

o

C)

– Best mechanical performance at high temperatures

– In-situ grown (tailorable) BN-based interphase composition

– Enables high temp processing routes not possible with other fiber-types, usually at temperatures well above the application use temperature!

0.01 0.1 1 10 100 1,000 50 100 200 300 500 1,000 Rup ture Stren g th , M P a 10 20 50 100 R u p tu re St re n g th , k s i Stress-Rupture Time, hr SylramicTM SylramicTM – i BN Hi-Nic.S Tyranno SA (1,2) 0.01 0.1 1 10 100 1,000 50 100 200 300 500 1,000 Rup ture Stren g th , M P a 10 20 50 100 R u p tu re St re n g th , k s i Stress-Rupture Time, hr SylramicTM SylramicTM – i BN Hi-Nic.S Tyranno SA (1,2)

1400C

DiCarlo and Yun, 2005 0

0.2 0.4 0.6 0.8 1 1.2 1.4 1000 1200 1400 1600 Anneal Temperature, oC RT No rm a li z e d Re ta in e d S tr e n g th Syl-iBN CVI; 100 hr anneal HNS CVI; 100 hr anneal Syl-iBN MI; 500 hr anneal

Yun, DiCarlo, Bhatt & Hurst, Ceram. Eng. Sci. Proc., 2003

(7)

Fiber Architectures that Enable Processing and

Properties for Desired Components

Approach

Æ

Process a wide variety of fiber-architectures

in order to (1) determine the effect of architecture on

composite properties for the purpose of tailoring

properties in desired directions and (2) determine if these

architectures could be successfully fabricated in order to

anticipate processing further architecture modifications.

(8)

Sylramic Fiber (COI) Fabric Low Temp. CVI Si-BN Interphase Infiltration CVI SiC Matrix Infiltration MI SiC/SiC Weaving Reactor Reactor Silicon Melt Infiltration Furnace CVI Preform

Slurry Cast SiC Matrix SiC/SiC

preform

Standard Slurry Cast Melt-Infiltrated (MI) 2D&3D

Woven Composites (GEPSC, Newark Delaware)

For Syl-iBN,

special treatment prior to CVI Si-BN

(9)

Tailoring Cracking Behavior with Fiber Architecture

(Syl-BN MI Composites)

• A variety of architectures are being studied for the

Syl-iBN MI system to determine effect of fiber

architecture and fiber content on matrix cracking

– 2D five harness satin with different tow ends per inch

• Standard composite (N24A) = 8 layers of balanced 7.9 epcm (20 epi)

– 2D five harness satin with different tow sizes

– 3D orthogonal with different Z fibers – balanced and

unbalanced in X and Y direction

– Layer to layer angle interlock

– Through the thickness angle interlock (with low Y fiber

content)

Unidirectional composite

– 2D five harness satin with high tow ends per inch in X

direction and rayon in Y direction

Unidirectional

composite

(10)

Some

Cross-Sections

5HS UNI

AI UNI

3DO-R

3DO-Z

LTL AI

Braid

2D 5HS

N24A

(11)

Determination of Fiber Volume Fraction

fo = fraction of fibers that bridge a matrix crack (0 = loading direction), including fibers at an angle, e.g., a braided architecture

tw

R

N

N

N

A

A

N

f

ply f tow tows ply f

c f f o 2 / /

π

=

=

t

R

epcm

N

N

f

o

ply

f

tow

f

10

2

/

π

=

Nf = total number of fibers in the cross-section of the tensile specimen,

Af = area of a fiber

Ac = cross-sectional area of the tensile specimen (tw) Nply = # of plys or layers through the thickness,

Nf/tow = # of fibers per tow (800

for Syl-iBN),

Ntows/ply = number of tows per

ply or layer

Rf is the fiber radius (5 mm or 0.005 mm for Syl-iBN).

epcm = tow ends per cm

w

epcm

N

tows ply

10

(12)

322 205

0.18 2

Same as 3DO-Bal-Z except oriented in the X (fill) direction (7 layer) 3DO-Bal-Z-X [7] 317 248 0.17 2.05

Nearly balanced 3D orthogonal; Y (loading) direction = Sylramic single tow at 7.1 epcm,8 layer; X direction = Sylramic double tow at 3.9 epcm; Z fiber = ZMI

3DO-Bal-Z-Y [7] 336 238 0.20 1.95

Nearly balanced 3D orthogonal; Y (loading) direction = Sylramic single tow at 7.9 epcm,8 layer; X direction = Sylramic double tow at 3.9 epcm; Z fiber = Rayon

3DO-Bal-R-Y [7]

352 250

0.26 Triaxial braid; double tow; -67/0/67 – tested in hoop orientation so

fibers are oriented + 23oto testing axis, 4 layers

Braid [8]

480 197

0.19 2.1

Balanced 2D five-harness satin ply lay up; two tows woven together at 3.9 epcm, 8 plys. 2D 5HS [6] (double tow) See [6] 220 to 290 0.12 to 0.2 1.5 to 2.2 Standard balanced 2D five-harness satin; ply lay up; number of plys

varied from 4 to 8; epcm varied from 4.9 to 8.7. 2D 5HS [6]

204 125

0.10 0.96

Layer-to-layer angle interlock; 5.5 epcm, 3 layers LTLAI (1)

596 262 + 9

0.27 1.58

Unbalanced 3D orthogonal; Y (loading) direction = Sylramic at 9.8 epcm, 7 layers; X direction = Sylramic at 3.9 epcm; Z direction = ZMI 3DO-Un-Z (2) >575 275 + 9 0.28 1.53

Unbalanced 3D orthogonal; Y (loading) direction = Sylramic at 9.8 epcm, 7 layers; X direction = Sylramic at 3.9 epcm; Z direction = Rayon 3DO-Un-R (2) >472 305 + 4 0.23 2.0

Unbalanced through-the-thickness angle interlock; fill direction = Sylramic at 11 epcm, 7 layers; warp direction = low epcm ZMI and rayon AI UNI (2) >818 335 0.50 2.17

Unbalanced five-harness satin; fill direction = Sylramic at 17 epcm; warp direction = low epcm rayon

5HS UNI (1) UTS (MPa) E (GPa) Fiber fraction, fo, in load direction Thickness (mm) Description Composite

(13)

Modal Acoustic Emission of CMCs

0 50 100 150 200 250 Time, microseconds -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 A m p li tu d e , m V 0 50 100 150 200 250 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 A m p li tu d e m V (Channel 1) (Channel 2) Extensional

Flexural(with some

superimposed extensional)

Reflections

Extensional

Reflections

Flexural(with some superimposed extensional)

Δtx 0 50 100 150 200 250 Time, microseconds -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 A m p li tu d e , m V 0 50 100 150 200 250 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 A m p li tu d e m V (Channel 1) (Channel 2) Extensional

Flexural(with some

superimposed extensional)

Reflections

Extensional

Reflections

Flexural(with some superimposed extensional)

Δtx AE AE AE AE Tabs Clip-on Extensometer x 25 mm a transducer AE AE AE AE Tabs Clip-on Extensometer x 25 mm a transducer

Locate damage events and failure events Æ Δt

Monitor stress(or time)-dependent matrix cracking Æ Cumulative AE Energy

•Identify damage sources, e.g. matrix cracks, fiber breaks Æ Frequency

(14)

RT 0

o

σ/ε

of Different Architecture

Syl-iBN MI Composites

0 100 200 300 400 500 600 700 800 900 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain, % Stress, MPa AI UNI, fo = 0.23 3DO Un-R fo = 0.28 5HS UNI fo = 0.5 3DO Un-Z fo = 0.27 Braid; fo = 0.26 5HS 7.9epcm fo = 0.19 (N24A) LTL AI fo = 0.1 3DO Bal-Z-Y;fo=0.17 5HS 4.7epcm fo = 0.12 3DO Bal-Z-X;fo=0.18
(15)

0

o

AE of Different Architecture Syl-iBN MI

Composites

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 200 400 600 800 1000 Stress, MPa Norm Cum AE AI UNI, fo = 0.23 5HS UNI fo = 0.5 3DO Un-R fo = 0.28 3DO Un-Z fo = 0.27 5HS 7.9epcm fo = 0.19 (N24A) LTL AI fo = 0.1

AE Onset (Matrix Cracking) Stress

3DO-Bal-Z-

(16)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0 0.1 0.2 0.3 0.4 0.5 0.6 fo A E O n set S tr a in , % 2D 5HS 3DO Bal-Y braid 5HS - double tow N24A 3DO Unbalanced AI UNI 5HS UNI LTL AI 3DO Bal-X 0 50 100 150 200 250 300 350 400 450 500 0 0.1 0.2 0.3 0.4 0.5 0.6 fo A E O n s e t S tr e s s , M P a 2D 5HS 3DO Bal-Y braid 5HS - double tow N24A 3DO Unbalanced AI UNI 2D 5HS UNI w/Rayon LTLAI 3DO Bal-X

(17)

Calculating the unbridged

tow area

90 20 1 h epcm N A = hs− ⋅ ⊥ ( z) towY z Y tow t h w h w epcm w epcm A ⎥⋅ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ + ⎪⎭ ⎪ ⎬ ⎫ ⎪⎩ ⎪ ⎨ ⎧ − + ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ⋅ = ⊥ 2 / 1 2 2 10 10 z ply z ply h tw N h w epcm t epcm N A= ⋅ = ⋅ 10 10 z tow h w epcm t epcm w epcm A ⋅ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎪⎭ ⎪ ⎬ ⎫ ⎪⎩ ⎪ ⎨ ⎧ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − + + ⋅ = − ⊥ 2 / 1 2 0 2 10 2 1 20 10 t w epcm A tow X x ⋅ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − = − ⊥ 10 ite Minicompos ite Minicompos h Length A⊥= ⊥ ⋅ ⊥
(18)

y = 231.07x + 36.034 y = 242.14x + 89.015 0 50 100 150 200 250 300 0 0.2 0.4 0.6 0.8 1 fo / (tow height) 1/2 A E O n set S tr ess, M P a 2D 5HS 3DO Bal.-Y Braid 2D 5HS - double tow 2D 5HS N24A 3DO Unbalanced - Y LTL AI 3DO Bal - X through-the-width not through-the-width

Effect of f

o

and max

tow size on Matrix Cracking Stress

y = 738.07x + 67.966 0 50 100 150 200 250 300 350 400 450 500 0 0.2 0.4 0.6 0.8 1 1.2 fo / (A)1/2 A E O n set S tr ess, M P a 2D 5HS 3DO Balanced braid 5HS - double tow N24A 3DO Unbalanced AI UNI 1/3 tow area AI UNI 2D 5HS UNI w/Rayon LTL AI 3DO Bal-X y = 650x2/3 y = 738.07x + 67.966 0 50 100 150 200 250 300 350 0 0.1 0.2 0.3 0.4 0.5 y = 650x2/3

f

o

/ (A

)

1/2

f

o

/ (tow height)

1/2
(19)

1315

o

C Creep-Rupture of Different Architecture Composites

Significant improvement (~ 100 MPa) in creep-rupture properties

for unbalanced fiber architectures with high fiber fraction in loading

direction over standard 2D five-harness composites

0 50 100 150 200 250 300 350 1 10 100 1000 Time, hr St re s s , M P a NASA N24A (fo=0.19) 3DO-Un-R (fo=0.28) 3DO-Un-Z (fo=0.27) AI-UNI (fo=0.23) failed well outside HZ ref. 15 ref. 14 ref. 16

(20)

Sylramic-iBN Reinforced SiC-based Matrix

Composites

Fabricate different matrix composites with the

same architecture:

8 ply, 7.9 epcm

(21)

Sylramic-iBN Composites: Processing Approaches

Woven Sylramic Preform

CVI Interphase

CVI SiC Partial Infiltration

SiC Slurry Infiltration

Si Melt Infiltration (MI)

Full CVI SiC CVI Si3N4 (thin)

PIP SiC or SiNC

Various fiber, interphase, and matrix treatments

to form iBN fiber and improve strength, creep,

cracking, and thermal properties

(22)

CVI SiC

CVI SiC

Composite

Composite

MI SiC

MI SiC

Composite

Composite

PIP

PIP

Composite

Composite

CVI PIP SiC

CVI PIP SiC

Composite

(23)

RT 0

o

σ/ε

behavior of Syl-iBN Composites

0

50

100

150

200

250

300

350

400

450

500

0

0.1

0.2

0.3

0.4

0.5

0.6

Strain, %

Stress, MPa

Syl-iBN MI SiC f = 0.39; E=250 GPa

hysteresis loops removed

Syl-iBN PIP SiC f = 0.50; E=160 GPa

Syl-iBN CVI SiC

f = 0.39 E = 275 GPa

Syl-iBN CVI-PIP SiC f = 0.39; E=230 GPa (failed in radius)

FIBER

DOMINATED

MATRIX

DOMINATED

(24)

Ultimate Properties: Fiber Strength After Processing

Degradation in PIP Composites

For the best PIP:

σ

fibers

~ 1600 MPa

0 50 100 150 200 250 300 350 400 450 500 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain, % Stress, MPa Syl-iBN MI SiC f = 0.39; E=250 GPa

hysteresis loops removed

Syl-iBN PIP SiC f = 0.50; E=160 GPa

Syl-iBN CVI SiC f = 0.39 E = 275 GPa

Syl-iBN CVI-PIP SiC f = 0.39; E=230 GPa

(failed in radius)

For CVI-based:

σ

fibers

~2350 MPa

Degradation in fibers

for PIP probably due

to inadequate

protection of fibers

(25)

Matrix Cracking (Acoustic Emission) of Syl-iBN

Composites

• For PIP (fiber dominated), very little AE activity and very little evidence of

stress-induced cracks – significant processing induced shrinkage cracks

• For MI, CVI, and CVI-PIP (matrix dominated), significant matrix cracking Æ

MI superior because pores are filled with silicon (removes stress

concentrators at tow intersections and induces residual compressive stress in matrix) 0 500 1000 1500 2000 2500 3000 0 100 200 300 400 500 Stress, MPa Cu mu lat ive AE En erg y MI SiC CVI SiC CVI-PIP SiC PIP SiC 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 100 200 300 400 500 Stress, MPa Norm Cum AE CVI-PIP SiC ~140 MPa CVI-SiC ~150 MPa MI-SiC ~180 MPa MI SiC CVI SiC

CVI-PIP SiC PIP SiC

PIP SiC has very little AE

activity

Design criteria for long term

use

(26)

Physical Properties of 2D-Woven Sylramic-iBN Panels

800 to 1600

(process

and filler)

2100 to

2400

(process)

~ 2400

~ 2400

Stress on

fibers at

failure, MPa

COIC

(Starfire

polymer)

GEPSC +

COIC

(Starfire

polymer)

GEPSC

Hyper-Therm

GEPSC

Goodrich

Composite

Vendors

Up to ~ 400

~ 400

~ 450

~ 450

UTS, MPa

~ 160

~ 210

~250

~ 250

E, GPa

~ 0.50

~0.38

~0.38

~0.38

f

~ 2.65

~2.70

~2.65

~2.75

Density,

g/cc

Syl-iBN PIP

Syl-iBN

CVI-PIP

Syl-iBN CVI

Syl-iBN MI

(27)

High Temperature 0

o

Creep Rupture Behavior

-Si containing MI matrix composites begin to

degrade due to Si diffusion and attack of CVI SiC

and fibers above 1350

o

C

-Therefore, tensile creep rupture tests were

performed between 1315

o

C and 1450

o

C in air to

(28)

Creep Rupture of Syl-iBN/SiC CMCs

1450

o

C Creep

-At 1315C, all composites survive 103 MPa (15ksi) for hundreds of

hours

-At 1450C, CVI, PIP and CVI-PIP composites survive 69 MPa

(10ksi) for hundreds of hours

-PIP composites rupture at the highest composite stresses

because they have the highest volume fraction of fibers

1315

o

C Creep

“Equivalent” is based on fo = 0.2

(29)

0

o

Creep Rupture Dictated by Fiber Rupture

Properties at High Temperatures (1315

o

C)

0 50 100 150 200 250 300 0 200 400 600 800 1000 Time, hr Rup

ture Stress, MPa

Syl-iBN MI Syl-iBN CVI Syl-iBN CVI-PIP Syl-iBN PIP PIP CVI SiC-Based 0 200 400 600 800 1000 0 200 400 600 800 1000 Time, hr S tress on fibers if fully loaded, MPa Syl-iBN MI Syl-iBN CVI Syl-iBN CVI-PIP Syl-iBN PIP 1315oC Creep Rupture

Composite creep-rupture at 1315oC appears to be dependent on stress on

fibers for the three composite systems

Starting strength of fibers in PIP matrix ranged from 1300 to 1600 MPa compared to ~2400 MPa for other systems. Æ Starting strength of fibers not a great factor for high temperature creep rupture

(30)

0

o

Creep Rupture Dictated by Fiber Rupture

Properties at High Temperatures (1450

o

C)

Composite creep-rupture at 1450oC appears to be dependent on stress on fibers for

CVI and PIP composite systems; however, MI creep-rupture significantly lower

Starting strength of fibers in PIP matrix ranged from 1300 to 1600 MPa compared to ~2400 MPa for other systems. Æ Starting strength of fibers not a great factor for high temperature creep rupture

0 20 40 60 80 100 120 0 100 200 300 400 500 600 S tr e ss, M P a 0 100 200 300 400 500 600 700 0 100 200 300 400 500 600 S tr e s s o n fib e rs if fu lly lo a d e d , M P a

1450

o

C

1450

o

C

MI CVI PIP MI CVI PIP
(31)

0

o

Creep Rupture of Composites are Comparable to

Fiber Rupture Properties at High Temperatures

Creep rupture life generally greater than comparable fiber-only

data, but follow same general trend

0 500 1000 1500 2000 2500 3000 0 10000 20000 30000 40000

Larson Miller Parameter, (T+273) [Log(t) +22]; T in oC, t in hr.

Stress on fibers, MPa

Syl-iBN MI Syl-iBN CVI Syl-iBN CVI-PIP Syl-iBN PIP Fiber Data Tow data 815C 1200C 1315C 1450C 0 500 1000 1500 2000 2500 3000 20000 25000 30000 35000 40000 45000

Larson Miller Parameter, (T+273) [Log(t) +22]; T in oC, t in hr.

Stress on fi be rs, MPa Syl-iBN MI Syl-iBN CVI Syl-iBN CVI-PIP Syl-iBN PIP Fiber Data 1200C 1315C 1450C

(32)

Out of Plane Properties for 2D-Woven Panels

1200

150

2000

25

Permeability,

mtorr/m**

4

10

5 {8}

--K33

(1400

o

C),

W/mK

8

28

18 {28}

25

K33 (25

o

C),

W/mK

23

10

7 {5}*

17

ILT strength,

MPa

Syl-iBN

PIP

Syl-iBN

CVI-PIP

Syl-iBN

CVI

Syl-iBN

MI

*{ } indicates after a special annealing treatment

(33)

Implications and Conclusions

• A plethora of properties (strength, thermal conductivity, permeability, etc…) can be tailored with the different SiC matrix processing routes available

– Further refinement and optimization can be made with architectures and heat treatments (not discussed in this presentation)

• High temperature creep rupture properties appear to be controlled by fiber creep rupture properties

– Starting strength of fibers not a factor at higher temperatures

– Nature of crack growth and fiber creep-rupture properties needs to be better understood to quantify life-degrading mechanism(s)

• High temperature (1400C+), highest stress capability is with PIP matrix composites because higher fiber volume fractions are attainable

However, for high thermal conductivity, high off axis in-plane strength, and

low permeability applications, CVI or CVI-PIP will be required – Fiber

fraction in desired directions could be increased with modified architectures to enhance properties

– The ability to better protect the fibers during PIP processing may result in higher use-stress capability or at least retained strengths

• Sylramic-iBN fiber-types are necessary to achieve maximum properties

– Other fiber types degrade with advanced processing temperatures and/or lack creep resistance

– Newer advances to Sylramic-iBN types (“Super Sylramic”) of fibers should increase high temperature performance

References

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