Development Status and Performance Comparisons of

1

Development Status and Performance Comparisons of

Environmental Barrier Coating Systems for SiC/SiC

Ceramic Matrix Composites

40th International Conference and Expo on Advanced Ceramics and Composites

January 24-29, 2016

Daytona Beach, Florida

Dongming Zhu and Bryan Harder

Environmental Effects and Coatings Branch

Materials and Structures Division

NASA John H. Glenn Research Center

Cleveland, Ohio 44135, USA

2

Light-Weight SiC/SiC Ceramic Matrix Composite (CMC) –

Environmental Barrier Coating (EBC) Development

Combustor Vane Blade

Monolithic/Hybrid

Ceramic Nozzles/Blades

Metal components with TBCs Light-weight SiC/SiC CMC

components

— Enabling next generation turbine engine hot-section technology: increased

materials temperature capability and improved future engine performance

— EBCs are critical to long-term environmental durability and life of Si-based

ceramic engine components

3

NASA Environmental Barrier Coating System Development – For

Turbine Engines

• Emphasize temperature capability, performance and durability for next generation for next generation vehicle airframe or engine systems

• Increase Technology Readiness Levels for component system demonstrations

2900°F

(T41)

Gas TBC Bond

coat

Metal

blade3200°F

(T41)

Gas TBC Bond

coat

Metal

blade3200°F

(T41)

Baseline metal

temperature

300°F

increase

Gas EBC Bond

coat

CMC

airfoil

Tsurface

Tsurface

Current metal turbine

airfoil system

State of the art metal turbine

airfoil system 2500°F TBCs

2700-3000°F CMC

turbine airfoil systems

200-500°F

increase

Tsurface

2500°F TBCs2700-3000°F

EBCs

Thin turbine

coating

development

2200°F TBCs2400°F CMCs

2700°F CMCs

4

Fundamental Recession Issues of CMCs and EBCs

Exposure Time (hrs)

0 20 40 60 80 100

SiC

Wt.

Lo

ss (

mg

/cm

2)

-15

-10

-5

0

1385 C

1446 C

1252 C

1343 C

SiO2 + 2H2O(g) = Si(OH)4(g)

Recession rate = constant xV1/2

P(H2O)

2/(P

total)1/2

Combustion gas

SiO2 + 2H2O(g) = Si(OH)4(g)

Combustion gas

Cooling air

(a) (b)

0.001

0.01

0.1

1

0.0005 0.00055 0.0006 0.00065 0.0007 0.00075 0.0008

AS800

SN282

SiC/SIC CMC

La2Hf

2O

7

HfO2 (doped)

RE-Hf-luminosilicates

BSAS

Spec

ific

wei

ght

chan

ge,

mg/c

m2-h

1/T, K-1

Supersonics EBC stability development goal - 2005

1300

Temperature, °C

14001500 12001600

SiC/SiC under high velocity

Rare earth silicates

BSAS Baseline

5

Outline─ Environmental barrier coating systems: design approach for

stability

─ Next generation environmental barrier coating systems for CMC

airfoils and combustors

• NASA coating technologies – advanced composition and system

development─ Fundamental research emphasis in understanding degradation,

property evaluation, and performance modeling

─ Multi-component, multi-layer and composite systems

• EBC processing: plasma spray, electron beam-physical vapor

deposition and plasma spray-physical vapor deposition

approaches

• Advanced testing methodologies and simulated engine heat flux

and stress testing

─ Laser high heat flux test rig and coating thermal conductivity

─ High temperature durability tests

─ Summary and Conclusions

6

Advanced Environmental Barrier Coating and

Architecture Development

— High temperature and environmental stability

— Lower thermal conductivity

— Balance designs of low thermal expansion, high strength and high strain tolerance

— High toughness

— Excellent resistance to thermal-mechanical loading, impact and erosion

— Interface, grain boundary stability and compatibility

— Dynamic characteristics to resist harsh environments and with self-healing capability

High temperature capable, high strength coatings

Energy dissipation and chemical

barrier interlayer

Environmental barrier

Ceramic matrix composite (CMC)

Nano-composite bond coat

Multilayer Architecture due to Performance Requirements

7

Advanced Environmental Barrier Coating Systems:

Coating Material System Developments and Architecture

• High-stability multi-component ZrO2/HfO2, Hafnium-Rare Earth (RE) silicates, or

Hafnium-Rare Earth (RE) aluminosilicate composites

• Alternating Composition Layered Composite (ACLC) and Sublayer EBCs

systems

– Advanced multi-component and RE silicate EBCs

– Oxide-Si composite bond coats, in particular, HfO2-Si bond coats

– Self-healing and protective coating growth capability

Multi-component RE and/or RE/Hf/Zr silicates

Ceramic composite bond coats

Interlayer: Compositional layer graded or composite systems

SiC/SiC CMCs

Low expansion high toughness HfO2/ZrO2, RE-HfO2-(Alumino)silicates

HfO2 and HfO2 composites

Doped mullite

with ACLC

(Hf rich bands)

Doped HfO2+Si and mullite/Si composite bond coat

(High temperature capable with self-healing)

Increased

SiO2 activity

Increased dopant RE/Transition

metal concentrations & increased

Al/Si ratio

8

Advanced Environmental Barrier Coating Systems

200 mm

Material Systems Temperature

capability

Thermal

expansion

Resistance to

oxidation and

combustion

environment

Mechanical

stability

HfO2-RE2O3 ~3000°C 8-10x10-6 m/m-K Excellent Excellent

HfO2-Rare Earth

silicates

~1900-2900°C 8-10x10-6 m/m-K Excellent Excellent

Rare Earth Silicates ~1800-1900°C 5-8.5x10-6 m/m-K Good Good

Rare earth –

aluminates and

Alumino silicates

~1600-1900°C 5-8.5x10-6 m/m-K Good Good

HfO2-Si and RE-Si

bond coat

Up to 2100°C 5-7x10-6m/m-K Good Excellent

9

EBC Processing using Atmospheric Plasma-Spray (APS)

and Hybrid Plasma Spray / Electron Beam - Physical

Vapor Deposition (EB-PVD) Coatings

Plasma-spray processing of

environmental barrier coatings

200 mm

Early generation hybrid environmental

barrier coatings systems processed

with combined Plasma Spray and EB-

PVD processing

EB-PVD Advanced HfO2

Plasma spray ytterbium silicate

Plasma spray HfO2-Si

10

EBC Processing using Plasma Spray and EB-PVD

HfO2-Si bond coat

Oerlikon Metco Triplex Processed Advanced EBCs

HfO2-Si bond coat

Directed Vapor EB-PVD Processed Advanced EBCs

11

EBC Processing using Plasma Spray - Physical Vapor

Deposition (PS-PVD)─ NASA advanced PS-PVD coating processing using Sulzer technology

─ EBC is being developed for next-generation SiC/SiC CMC turbine airfoil coating processing

• High flexibility coating processing – PVD, CVD and/or splat coating processing

• High velocity vapor, non line-of-sight coating processing for complex-shape components

NASA Hybrid PS-PVD coater system

PS-PVD processed

coatings

Nozzle section view Mid section view End section (sample side) view

Vapor ZrO2-

Y2O3 coatingSplat/partial

vapor Yb2Si2O7

10 mm

HfO2-Si bond

coat

12

Laser High Heat Flux Approach

– Turbine level high-heat-flux tests crucial for CMC coating system developments

– Real-time thermal conductivity measurments

– Advanced complex combined mechanical loading conditions and environments

incorporated

T

Dis

tan

ce

fro

m s

urf

ac

e

Heat flux

cooling

Turbine: 450°F across 100 microns

Combustor:1250°F across 400 microns

Test rig

Thermal gradients:

13

Real-Time Thermal Conductivity Measurements

and Damage Monitoring

Surface flow

14

Plasma Spray EBC Processing and Heat Flux Testing

for CMC Component EBC Validations

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 20 40 60 80 100 120

EBC System 6, 1360°C







EBC System 6 Inner Diameter (ID) liner coating, 1500°C

Th

erm

al

co

nd

ucti

vit

y,

W/m

-K

Th

erm

al

co

nd

ucti

vit

y,

W/m

-K

Time, hours

Failure

FailureFailure

─ Advanced plasma sprayed multicomponent HfO2-rare earth silicate with HfO2-Si based

environmental barrier coating optimized and down-selected

─ Thermal conductivity ranged from 0.4 – 1.7 W/m-K

Laser heat flux test under thermal

gradients

15

Thermal Conductivity of PS-PVD Yb2Si2O7 Coatings For

Process Optimization

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Yb2Si2-xO7-x System 1







k0

k2

Thermal conductivity, W/m-K

breakdown

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60

b/a=0.05

b/a=0.2

b/a=0.25

Ther

mal

conduct

ivit

y, W

/m-K

Porosity, %

Coating System 2: porosity 16% modeled vs 13% measured

Coating System 3: porosity 28% modeled

Coating system 4: porosity 18% modeled

Coating system 6: porosity 20% modeled

Coating 2

Coating 3

Coating 4

Coating 6

─ Processing and microstructural optimizations,

aiming at achieving coating stability and

maintaining lower thermal conductivity

System 2

Thermal conductivity modeled using FEM

16

PS-PVD Ytterbium Silicate EBC Tested in Heat Flux

Conditions

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60

kcera

TsurfaceTinterfaceTbackqthru

Th

erm

al c

on

duct

ivit

y,

W/m

-K

Tem

per

ature

, °C

Time, hours

Tinterface=1120°CTsurface=1400°C

Tback=920°C

Three layer HfO2-ytterbium silicate-Si

completed 50hr laser heat flux thermal

conductivity-durability tests in air and

steam

─ Demonstrated initial durability of HfO2-ytterbium silicate-silicon at 1400-1500°C test

temperatures in air and laser heat flux steam tests

─ Thermal conductivity ranged from 0.6 to 2.5 W/m-K

─ Achievable low thermal conductivity and unique structures with coatings

Laser heat flux steam test

17

PS-PVD Ytterbium Silicate EBC Tested in Heat Flux

Conditions - Continued

─ Demonstrated initial durability of ytterbium silicate

with advanced HfO2-Si bond coats at 1400-1500°C

test temperatures in air and laser steam tests

─ Thermal conductivity ranged from 0.6 to 2.5 W/m-K

─ Some sintering led more significant thermal

conductivity increases

PS-PVD processed Ytterbium/HfO2-Si

bond coat

50 mm

PS-PVD processed composite HfO2-Si

bond coat

0

2

4

6

8

10

0

200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25

kcera

Tsurface = 1482°CTinterface = 1420°CTback=1310°C

Th

erm

al c

ond

uct

ivit

y, W

/m-K

Tem

per

atu

re, °C

Time, hours

Laser heat flux test

18

Composite EBCs Considered for Improved Stability –

Process also developed for EBC systems

0 50 100 150 200 250 300 350

Yb2Si2O7/Yb2SiO5

Multi-component HfO2(t',m)+Yb2Si2O7/Yb2SiO5 30:70



Multi-component HfO2(t',m)

Biaxial strength, MPa

- Layered and nano-composite designs incorporated in various processing

approaches

- Advanced composite systems shown to improve the temperature capability and

recession resistance

- Improved mechanical properties for erosion and impact resistance

- Improved CMAS resistance

19

EB-PVD Composite Environmental Barrier Coatings –

CMAS Reaction Tested HfO2-Si bond coat

EB-PVD Processed EBCs: alternating HfO2-rich and ytterbium silicate layer

systems for CMAS and impact resistance

20

Advanced NASA 2700°F HfO2-Si and Rare Earth-Si Based

Bond Coats

SiC

RESi(O)

RE2Si2O7-x

20 mm

F

G

EDS F

EDS G

Microstructure of a HfO2-doped (Yb,Y)Si(O)

bond coat

EDS A

EDS C EDS B

- Continued improvements in processing

robustness and composition

optimization

21

Advanced EBC Successfully Tested under 1000 hr Stress-

Rupture Conditions at 2700°F

- EBC systems tested included various processed APS and EB-PVD EBCs

Cooling shower

head jets

Test specimen

High

temperature

extensometer

Laser beam

delivery optic

system

To

tal

stra

in, %

0.0

0.2

0.4

0.6

0.8

1.0

0 200 400 600 800 1000 1200

Time, hours

Tsurface = 2700°F

Tinterface= 2500°F

TCMC back=2320°F

Tsurface = ~2500°F

Tinterface= 2350°F

TCMC back=2200°F

Gen II CMC, 1.98x10-7

/s; 15 ksi

Gen II CMC, 7.35x10-8

/s; 15 ksi

Gern I CMC 4.10x10-8

/s; 10 ksiTsurface =~2500°F

Tinterface=~2350°F

Tback=~2200°F

Tsurface = 2400ºF

Tinterface = 2300ºF

Tback = 2050ºC

Gen I CMC, 7.19x10-8

/s; 15 ksi

Microstructures after 1000 hr, 1482°C (2700°F),

1371°C (2500°F),103 MPa (15 ksi) testing

22

Advanced EBC-CMC Fatigue Test with CMAS:

Successfully Tested 300 h Durability in High Heat Flux

Fatigue Test Conditions - A thin EB-PVD turbine airfoil EBC system with advanced HfO2-rare earth silicate

and GdYbSi (controlled oxygen activity) bond coat tested at TEBC-surface 1537°C,

Tbond coat 1480°C, Tback CMC surface 1250°C

- Fatigue Stress amplitude 69 MPa, at mechanical fatigue frequency f=3Hz, stress

ratio R=0.05

- Low cycle thermal gradient fatigue 60min hot, 3min cooling

Strain amplitude

1537°C, 69MPa (10ksi), 300 h fatigue (3 Hz, R=0.05) on

14C579-011001_#8 CVI-MI SiC/SiC (with CMAS)

Fatigue strain-time plot

Fatigue temperature-time plot

23

Advanced EBC Fatigue Creep-Fatigue of EBCs-CMCs in

Complex Heat Flux and Simulated Engine Environments

0

50

100

150

200

250

0 0.1 10 1000 100000 10000000

10-7

10-5

0.001 0.1 10 1000

Max

imu

m s

tres

s, M

Pa

Fatigue cycles

High temperature strength data

Fatigue or creep hot time, hours

EBC 2700F+; CMC temperature labeled (2550-2700F)

2550F2700F

• Long-term creep and fatigue validated EBCs and CMCs at various loading levels

• Demonstrated advanced 1482°C (2700°F) EBC and bond coat capabilities in

complex environments

• Advanced coatings have minimized environment degradations of CMCs,

demonstrating durability in fatigue and CMAS environments

Stress-oxidation and stress-CMAS environmental testing summary

24

Summary and Conclusions

• Advanced EBCs being developed and evaluated using APS, hybrid APS/EB-PVD, EB-

PVD and, PS-PVD

─ Achieved advanced composition designed EBCs

─ Significantly expanding envisioned high performance coating architecture development

─ Demonstrated initial durability

• Advanced, high temperature testing approaches showed significant advantages in

the development of advanced environmental barrier coating systems

─ Simulated engine thermomechanical conditions

─ Simulated environment conditions

─ Real time thermal conductivity, stability and durability

─ Capable quantifying the EBC degradation and performance

25

Acknowledgements

The work was supported by NASA Fundamental Aeronautics Program (FAP)

Transformational Tools and Technologies Project.

The authors would like to acknowledge the contributions and helpful discussions from

the following:

• Ron Phillips (Vantage Partners, LLC), mechanical testing

• Terry McCue (SAIC/NASA GRC, SEM/EDS)

• Joy Buehler (Vantage Partners, LLC, Met Lab)

• James A. DiCarlo, James L. Smialek, Janet Hurst, Dennis Fox, Robert A. Miller,

and Nate Jacobson (NASA GRC)

NASA Fundamental Aeronautics Program (FAP)

Documents

Development Status and Performance Comparisons of