National Aeronautics and Space Administration6th International Conference on High Temperature Ceramic Matrix Composites (HTCMC-6), New Delhi, India, September 4-7, 2007 Current Challenges

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National Aeronautics and Space Administration

www.nasa.gov

Abstract for Invited Plenary Presentation at the6th International Conference on High Temperature Ceramic Matrix Composites

(HTCMC-6),New Delhi, India, September 4-7, 2007

Current Challenges for HTCMC Aero-Propulsion ComponentsJames A. DiCarlo, NASA Glenn Research Center, Cleveland, OH 44135

In comparison to the best metallic materials, HTCMC aero-propulsion engine components offer the opportunity of reduced weight and higher temperature operation, with corresponding improvements in engine cooling requirements, emissions, thrust, and specific fuel consumption. Although much progress has been made in the development of advanced HTCMC constituent materials and processes, major challenges still remain for their implementation into these components. The objectives of this presentation are to briefly review (1) potential HTCMC aero-propulsion components and their generic material performance requirements, (2) recent progress at NASA and elsewhere concerning advanced constituents and processes for meeting these requirements, (3) key HTCMC component implementation challenges that are currently being encountered, and (4) on-going activities within the new NASA Fundamental Aeronautics Program that are addressing these challenges.

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Current Challenges for HTCMCAero-Propulsion Components

J.A. DiCarloStructures and Materials and Division

NASA Glenn Research CenterCleveland, OH 44135

USA

Invited Talk Presented at HTCMC-6September, 2007, Delhi India

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Background

A major thrust under a variety of recent NASA and DoD aero-propulsion programs is to develop and demonstrate advanced lightweight components with optimized structural and environmental durability at service temperatures significantly higher than current metallic alloysPotential Benefits:• Higher engine efficiency and thrust• Reduced weight and emissions • Longer and more reliable component life• Enabling of other aerospace applications not

attainable with metals

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Lightweight High-Temperature Structural Materials areNeeded for Multiple Aero-Propulsion Components

Control Surfaces

Nose Caps, Leading Edges

Turbine Vanes and

Blades

Nozzle Flaps and Seals

Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panelsand Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panels,Thrusters,

Rocket Nozzles

Combustor Cooled

Control Surfaces


Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panelsand Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panels,Thrusters,

Rocket Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panelsand Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panels,Thrusters,

Rocket Nozzles

Combustor Cooled

Control Surfaces


Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panelsand Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panels,Thrusters,

Rocket Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panelsand Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panels,Thrusters,

Rocket Nozzles

Combustor Cooled

Control Surfaces


Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panelsand Nozzles

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Panels,Thrusters,

Combustor Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

PanelsCombustor

Cooled

Turbine Vanes and

Blades


Combustors

Turbine Shrouds

Cooled

Turbine Vanes and

Blades


Combustor Liners

Turbine Shrouds

PanelsCombustor

ActivelyCooled

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Typical Function of a Structural MaterialIn a Hot Aero-Propulsion Component

Key Component Property Needs:• Low Density, Low Permeability, High Emissivity• High Maximum Temperature Capability• High Tensile Stress Capability In-Plane and Thru-Thickness• High Thermal Conductivity Thru-Thickness to reduce thermal gradients and stresses

Max TensileStress

Qout (radiation)Hot gas layer

Cooling fluid layer

ΔTH

ΔTB

ΔTW

ΔTC

Thermal /Environmental Barrier Coating

Thin-Wall Component

Max Material T

Qin

Qout (conduction)

Max In-PlaneTensileStress

Qout (radiation)Hot gas layer

Cooling fluid layer

ΔTH

ΔTB

ΔTW

ΔTC


Thin-Wall Component

Max Material T

Qin

Qout (conduction)

Hot gas layer

Cooling fluid layer

ΔTH

ΔTB

ΔTW

ΔTC


Thin-Wall Component


Thin-Wall Component

Max Material T

Qin

Qout (conduction)

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Advantages of SiC Fiber / SiC Matrix (SiC/SiC)High-Temperature Ceramic Matrix Composites

versus Superalloys:- Lower density (~30% metal density)- Higher temperature capability (>1100oC)- Lower thermal expansion

versus Monolithic Ceramics:- Non-catastrophic failure- Higher toughness, better damage tolerance- Capability for larger and more complex shapes

versus Carbon Fiber Composites (C/SiC, C/C):- Higher oxidative durability, more predictable life- Lower permeability

versus Oxide/Oxide Ceramic Composites:- Higher strength, temperature capability, creep-

rupture resistance, thermal conductivity, emissivity- Lower permeability

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NASA Advancements in SiC/SiC Constituents and Processes that address Key Property Needs

for Aero-Propulsion Components

• Sylramic-iBN fiber (creep resistant stoichiometric SiC with protective in-situ grown BN coating and thermal stability >1600oC)

• Improved 2D and 3D Fiber Architectures (stress-free and high thermal conductivity)

• Improved CVI SiC Matrices (higher thermal conductivity and creep-resistance)

• Hybrid CVI + PIP SiC Matrices (silicon-free for thermal stability >1500oC)

• Advanced Environmental Barrier Coatings (EBC)(thermal stability >1500oC in combustion environments)

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Stress-Rupture Temperature, oC

0

20

40

60

80

100

120

140

160

900 1000 1100 1200 1300 1400 1500

Rup

ture

Str

engt

h S x

, MPa

SiC/SiC with Syl-iBN fibers + Si-free matrices

Ox-Ox CMC

~Best Superalloy SiC/SiC with

Syl-iBN fibers +CVI/MI matrices

AS-800 Si3N4

~Max in-plane stress for

SiC/SiC liners and vanes

Thermostructural capability for NASA SiC/SiC system is state-of-the art with upper use temperature of ~1450oC (2640oF) for liners and vanes

500-Hour Rupture Strength in Air for ReusableHigh-Temperature Structural Materials

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Fiber and Architecture Effects onSiC/SiC Thru-thickness Properties

3D Architectures and Sylramic-iBN Fibers Significantly Improve SiC/SiC Thru-thickness Conductivity and

Thru-Thickness Tensile Strength (TTTS)

0

5

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1000 1200 1400Temperature, oC

Thru

- Thi

ck T

herm

al C

ondu

ctiv

ity, W

/m

.o

2D Hi-Nic-S/CVI-MI

ILTS: 15 MPa

ILTS: 25 MPa

2.5D Sylramic-iBN/CVI-PIP Anneal

2D Syl-iBN/CVI-MI

0

5

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1000 1200 1400Temperature, oC

Thru

- Thi

ck T

herm

al C

ondu

ctiv

ity,

W/m

.o C

2D Hi-Nic-S/CVI-MI

TTTS: 15 MPa

TTTS: 25 MPa

3D Sylramic -iBN/CVI-PIP Anneal

2D Syl-iBN/CVI-MI √

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• Combustor liners• Turbine vanes and blades• Turbine shrouds• Thrusters• Nozzle Flaps and Seals• Heat exchangers• Integral Rotors

NASA and DOD have produced a Variety of Prototype SIC/SIC Aerospace Components

Vane 2/Lot 1Vane 2/Lot 1

But Multiple Challenges Still Exist Before Aero-Propulsion Components Based on

High Performance SiC/SiC HTCMCCan Become Actual Products

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Objective / Outline

• Present brief overview of key current R&D challenges that need to be addressed for viable SiC/SiC aero-propulsion components:

Performance:Higher matrix cracking strength

Producibility:Complex-shaped fiber architectures

Design Methodologies:Creep and Finite Element (FE) lifing models

Affordability:Lower material and fabrication costs

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Challenge: Higher Matrix Cracking Strength

• Generally it is currently assumed EBC are prime-reliant and SiC/SiC components can be designed with service-related stresses below matrix cracking to minimize environmental attack.

• Thus, besides the development of reliable EBC, the challenge also exists to understand the sources of matrix cracking and minimize their influence.

• For highly dense matrices, such as those formed by melt infiltration, the fiber architecture plays a strong role in the initiation of thru-thickness matrix cracks.

• NASA is currently studying this effect using Acoustic Emission and a variety of Sylramic-iBN fiber architectures.

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SiC/SiC Matrix Cracking vs. Fiber Architecture

3D OrthogonalAngle Interlock

Braid2D Five-harness Satin

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

Nor

m C

um A

E

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 Fill

The in-plane onset stress for thru-

thickness cracking can be increased from 100

to ~300 MPa by proper architecture

selection

AE

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Thicker Suction Side Wall or Ribneeded to avoid

“Ballooning”stresses

at Leading and Trailing Edges due to internal

higher pressure cooling air

Tapered Wall

Thicknessat Trailing

Edge

High Stress andHigh Temperatureat Leading Edge

High Stress Area

High Temperature Area

Cooling Holes

Hot Combustion Gas Flow

Pressure Side Wall

Challenge: Fiber Architectures for Complex-Shaped High-Performance

Components such as Turbine Airfoils

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• Fiber architectures for aero-propulsion components must not only provide structural properties required at practically all locations in component, but also meet the component shape requirements. 3D is preferred because of better delamination resistance and thermal conductivity.

• Currently for complex-shaped SiC/SiC components such as vanes and blades, it is practically impossible for any single 2D or 3D architecture to simultaneously achieve all structural and shape requirements

• Some key areas of concern include bending and residual stresses in high-performance high-modulus SiC fibers, and architectures that can simultaneously provide smooth component surfaces, T-sections at reinforcement ribs, and thin trailing edges.

Current Producibility Issues for Complex-Shaped SiC/SiC Aero-Propulsion Components

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• For SiC/SiC to be reliably implemented in aero-propulsion components, there has to exist design and lifing data bases for selection of constituent materials, processes, and architecturesthat will yield components with directional strength properties safely below predicted component stress states at the end of thedesired component service life.

• These needs have been difficult to address due to such issues as the high cost for obtaining design and lifing data bases, the problems in matching the architectural requirements for structural properties with those for component shape requirements, and the current lack of robust modeling approaches for converting the numerous CMC lifing mechanisms into Finite Element codes.

Challenge: SiC/SiC Design Methodologies

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Mechanistic Modeling Needed for Creep Effects

THot : compressive surface

TCold : tensile surface

ΔTW= X

ΔTW= 0 ΔTW= X

stress relaxationon both surfaces

due to creep

room temperature

ΔTW= 0

Adverse residual tensile stress

on outer surface on cool-down

room temperature

t = 0

t > 0

inQ

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Challenge: SiC/SiC Component Affordability

Cost is still a major issue:– High cost for high performance SiC fiber– Constituent, composite, and EBC vendors are often

different and single organizations, complicating production time, availability, and resulting in multi-tiers of profit taking

– Considerable hand-labor required for complex shapes– Process technologies are continually being optimized– Quality control at every process step is costly– Reliable life-cycle cost-benefit analyses need to be

conducted to determine economic viability

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Summary • SiC/SiC systems with high performance fibers are capable of

outperforming the best superalloys and ox/ox CMC systems in weight-savings, structural capability, upper use temperature, and thru-thickness thermal conductivity.

• However, these systems currently face a variety of key challengesthat need to be overcome before they can be widely implemented in hot-section aero-propulsion components: – 3D fiber architectures that not only yield high matrix cracking

strengths both in-plane and thru-thickness, but also are conducive for the fabrication of complex-shaped components. If the proper SiC fibers are selected, such as Sylramic-iBN, 3D systems should also provide improved thru-thickness thermal conductivity and impact resistance.

– Advanced lifing design methodologies that can not only account for environmental effects, but also residual stress effects due to creep.

– Lower cost materials and processes and a more stream-lined vendor base for improved affordability and wider market interest.

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Outlook for SiC/SiC Components• SiC/SiC systems will continue to be considered for a

variety of hot aero-propulsion components due to their capability to outperform monolithic ceramics in damage tolerance and metallic superalloys in upper use temperature and reduced weight.

• Commercialization of SiC/SiC technologies within the next 5 to 10 years is likely for medium to large-sized components that are thin-walled and relatively simple in shape (combustor liners, transition pieces, seal rings, shrouds, etc.).

• For the more complex-shaped and higher performing components, such as turbine vanes and blades, some of the key technical and economical challenges discussed here are currently being addressed under the new NASA Fundamental Aeronautics Program.

Contact: [email protected]

Documents

National Aeronautics and Space Administration6th International Conference on High Temperature Ceramic Matrix Composites (HTCMC-6), New Delhi, India, September 4-7, 2007 Current Challenges