1

Environmental Barrier Coatings for Turbine Engines:

Current Status and Future Directions

Dongming Zhu

Durability and Protective Coatings Branch

Materials and Structures Division

NASA Glenn Research Center

Cleveland, Ohio 44135, USA

The International Conference on Metallurgical Coatings and Thin Films (ICMCTF)

San Diego, California

May 1, 2013

2

Outline

─ Environmental barrier coating system development: needs,

challenges and limitations

─ Advanced environmental barrier coating systems for CMC

airfoils and combustors • NASA EBC systems and material system evolutions

• Current turbine and combustor EBC coating emphases

• Advanced development and testing approaches

• EBC and bond coats: recent developments

─ Design tool and life prediction of coated CMC components

─ Advanced CMC-EBC rig demonstrations

─ Summary and future directions

3

Durable Environmental Barrier Coating Systems for

Ceramic Matrix Composites (CMCs): Enabling Technology for Next Generation Low Emission, High

Efficiency and Light-Weight Propulsion

— NASA Environmental barrier coatings (EBCs) development objectives

• Help achieve future engine temperature and performance goals

• Ensure component system durability – working towards prime reliant coatings

• Establish database, design tools and coating lifing methodologies

• Improve technology readiness

Fix Wing Subsonic Aircraft Supersonics Aircraft

4

NASA Environmental Barrier Coating System

Development

– EBCs enable next generation SiC/SiC CMC combustor and turbine airfoil component technologies for reduced turbine engine NOx emission, cooling requirements and engine weight, while helping improving engine efficiency

– Next generation high pressure turbine airfoil EBCs with advanced CMCs emphasized

Instability

Control Fuel

Staging

CMC

Liners

Multipoint

Injection

Low emission combustor

Advanced core technologies – HPT first stage

CMC vanes and future turbine blades

5

NASA Environmental Barrier Coating Development Goals

* Recession: <5 mg/cm2 per 1000 hr (40-50 atm, Mach 1~2)

** Component strength and toughness requirements

• Emphasize temperature capability, performance and durability

– Low silica activity silicate and high stability/high toughness oxide system developments

• Develop innovative coating technologies and life prediction approaches

• 2700°F (1482°C) EBC bond coat technology for supporting next generation

• 2700-3000°F (1482-1650°C) thin turbine and CMC combustor coatings

– Meet 1000 hr for subsonic aircraft and 9,000 hr for supersonics/high speed aircraft hot-time life requirements

2400°F (1316°C) Gen I and Gen II SiC/SiC

CMCs

3000°F+ (1650°C+)

Gen I

Temperature

Capability (T/EBC) surface

Gen II – Current commercialGen III

Gen. IV

Increase in T

across T/EBC

Single Crystal Superalloy

Year

Ceramic Matrix Composite

Gen I

Temperature

Capability (T/EBC) surface

Gen II – Current commercialGen III

Gen. IV

Increase in T

across T/EBC

Single Crystal Superalloy

Year

Ceramic Matrix Composite

2700°F (1482C)

2000°F (1093°C)

Step increase in the material’s temperature capability

3000°F SiC/SiC CMC

airfoil and combustor

technologies

2700°F SiC/SiC thin

turbine EBC systems for

CMC airfoils

2800ºF

combustor

TBC

2500ºF

Turbine TBC 2700°F (1482°C) Gen III SiC/SiC CMCs

6

NASA EBC Technology Development

- Also Supported Other National SiC/SiC CMC and Si-base

Ceramic Development Programs

NASA – EPM

2300 - 2400 F EBC

(TRL of 3)

NASA- UEET-2700°F EBC Development,

NASA 3000°F Multifunctional T/EBC Development

New Compositions, SiC/SiC Vane, Cooled Si3N4 Vane

(TRL of 4)

DOE-CFCC

EBC (TRL 4-5) DOE - EBC Improvements (TRL of 4-5)

NASA Steam Rig Testing

High Pressure Burner Rig, Atm. Burner rig, Laser Rigs, Furnace (TRL of 5)

DOE - Keiser Rig

DOE - Field Tests (TRL of 6 and higher)

DoD-IHPTET Core and Engine Test (TRL of 6)

- FY99 FY00 FY01 FY02 FY03 FY04 FY05 FY06 FY07 FY09 - present

DoD - Honeywell, Rolls Royce,

GE components (TRL 6)

1 2

1 Si3N4 vane HPBR test 2 3000°F CMC demonstration

NASA FAP Supersonics Turbine Engine

CMC Thin Blade Coating

Development, AeroSciences EBCs (TRL-2 to 4)

0

0 3100°F CMC vane testing

NASA ERA (TRL-4

to 5)

National Aeronautics and Space Administration

www.nasa.gov

NASA High Pressure Burner Rig Testing Capabilities for

Turbine Airfoil and Combustor CMC-EBC Testing

7

─ Jet fuel & air combustion with mass air flow 2.0 lbm/s (~1kgm/s) and gas temperature 3000°F+ (1650°C+)

─ Adjustable testing pressures from 4 to 16 atmospheres, independent controls of sample temperature, testing pressure, and gas velocity

─ 30/48 kW cooling air heater systems for 1200°F (650°C) cooling air ─ Up to 850 m/s combustion gas velocity in the turbine testing section ─ Cooled, pressurized (600 psi) coupon specimens, subelements and subcomponents testing

Combustor

section

Burner nozzle High pressure burner rig

Burner nozzle

(2” dia) and duct

Combustor

specimen test

section

Heated cooling air Specimen test

section

2” diameter disc

CMC test specimen

Pyrometer surface temperature

measurements through viewports

1High pressure burner rig

8

NASA High Power CO2 Laser Based High Heat Flux

Testing for SiC/SiC and Environmental Barrier Coatings

Development – Test rigs capable of turbine level high-heat-fluxes and with simulated

mechanical loading and water vapor enviornments

– Crucial for advanced EBC-CMC developments

T

Dis

tan

ce

fro

m s

urf

ac

e

Heat flux

Cooling – high velocity air or air-water mist

Achieved heat transfer coefficient 0.3 W/cm2-K

Turbine: 450°F across 100 microns

Combustor:1250°F across 400 microns

Coupon specimen test

9

NASA High Power CO2 Laser Based High Heat Flux

Testing for SiC/SiC and Environmental Barrier Coatings

Development - Continued – Combined high heat flux, mechanical loading and water vapor test condition to

study heat flux thermal cycling, stress rupture, fatigue and environment interactions

Steam during

cooling cycles

High temperature testing

with steam flow

Cooling

shower head

jets

Test

specimen

High

temperature

extensometer

Laser beam

delivery

optic system

Laser heat flux

(b) High heat flux flexural TMF testing: HCF,

LCF, interlaminar and biaxial strengths

Ring-on-Ring

2” beam size

subelement test

(a) Tensile rupture

flexural

(c) High heat flux and high steam (d) Subelements

10

Fundamental Recession Issues of CMCs and EBCs

- Recession of Si-based Ceramics

(a) Convective; (b) Convective with film-cooling

- Low SiO2 activity EBC system development emphasis

- Advanced rig testing and modeling

More complex recession behavior of CMC and EBCs in High Pressure Burner

Rig

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

Recession rate = const. V1/2 P(H2O)2/(Ptotal)

1/2

Combustion gas

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

Combustion gas

Cooling gas

(a) (b)

11

Fundamental Recession Issues of CMCs and EBCs -

Continued

Combustor coating Turbine coating

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

Robinson and Smialek, J. Am. Ceram Soc. 1999

- Early generation coatings - EBC systems

Weight Loss of SiC in High Pressure

Burner Rig

6 atm 20 m/s

12

NASA Environmental Barrier Coating Technology

Development ― Major advanced environmental barrier coating development milestones:

• EPM Gen I EBC: BSAS/Mullite+BSAS/Si (1995-2000)

• UEET Gen II EBC: RE2Si2O7 or RE2SiO5/BSAS+Mullite/Si (2000-2004)

• UEET Gen III EBC: 2700-3000°F EBC systems including advanced HfO2 systems with

Oxide+Si bond coats and Si-based ceramic component demonstration (2000-2004)

– also advanced mullite was considered more stable than BSAS – modified mullite

developments; many top coat materials

• FAP Gen IV EBC: 2700°F multi-component, nano-composite graded oxide/silicate

turbine thin coating systems including advanced nano-composites with SiC nanotube

reinforced bond coats (2005-2011)

• NASA FAP and ERA Gen V EBC: addressing the development of thin, very strong,

durable 2700-3000°F turbine blade coatings; and hybrid advanced CMC combustor and

vane EBCs (2009-present) - 5 mil (127 micrometer), thin turbine EBC for SiC/SiC CMC blade, requiring advanced vapor

processing

- 5-10 mil (127-250 micrometer), thin CMC turbine vane coating, requiring advanced vapor

processing

- 15 mil (380 micrometer), thick CMC combustor coating, requiring advanced air plasma spray (APS)

or hybrid plasma spray – physical vapor deposition processing

13

Environmental Stability of EBC Systems

Stability of selected coatings systems

0.001

0.01

0.1

1

10

0.0005 0.00055 0.0006 0.00065 0.0007 0.00075 0.0008

BSAS baseline

SiC/SIC CMC

AS800

SN282

BSAS

La2Hf2O7

HfO2 (doped)

HfRE Aluminosilicate

Yb-Silicate

SiC/SiC CMC (200 m/s)

Tyranohex SA SiC composite (200m/s)

BSAS (200m/s)

HfO2-1 (200 m/s)

Sp

ecif

ic w

eigh

t ch

ang

e, m

g/c

m2-h

1/T, K-1

NASA EBC development stability goal

1300

Temperature, °C

14001500 12001600

SiC/SiC under high velocity

BSAS Baseline

1100 1000

Stability and temperature capability improvements

through coating composition and architecture innovations

Gas pressure 6 atm

Gas velocity 30m/s

Gas

velocity

200m/s 2011

Stability of selected coatings systems

2011

HfO2 and ZrO2 systems

HfO2-RE oxide silicate and aluminate systems

Silicate and RE-silicate systems

SiC/SiC systems

Activation energy

273 kJ/mol

14

Advanced Environmental Barrier Coating System

Requirement Concepts under NASA 3000°F EBC coating

Program 2000-2004

1650°C capable thermal/environmental

and radiation barrier

Energy dissipation and chemical

barrier interlayer

Environmental barrier

Ceramic matrix composite (CMC)

Nano-composite bond coat

— High temperature and environmental stability

— Low thermal conductivity supporting thin-coating configurations

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

— High toughness

— Excellent thermal-mechanical stress, creep, fatigue, erosion and recession resistance

— Interface, grain boundary stability and compatibility

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

— Functionality, in particular to support health monitoring and 3-D full field strain measurements

Environmental Barrier Coatings provide environmental and thermal barrier

(protection) capabilities for Si-based ceramic matrix composite systems

15

Environmental Barrier Coating Development: Challenges

and Limitations ─ Current EBCs limited in their temperature capability, water vapor stability

and durability, especially for advanced high pressure, high bypass turbine

engines • Thin turbine coating configuration imposes greater challenges because of the

requirements of significantly lower recession rates and reduced EBC system

reactivity

─ Advanced EBCs also required significantly higher strength and toughness • In particular, resistance to combined high-heat-flux, engine high pressure,

combustion environment, creep-fatigue loading interactions

─ EBCs need improved erosion, impact and calcium-magnesium-alumino-

silicate (CMAS) resistance and interface stability • Critical to reduce the EBC Si/SiO2 reactivity and their concentration tolerance

• Temperature is a key

─ EBC-CMC systems need advanced processing for realizing complex

coating compositions, architectures and thin turbine configurations for

next generation high performance engines • Advanced high temperature processing of nano-composites using Plasma Spray,

Plasma Spray - Physical Vapor Deposition, EB-PVD and Directed Vapor EB-PVD

16

Interface Reactions of Si-BSAS Based EBC Systems after

Testing at the Interface Temperature of 1300°C — Significant interfacial pores and eutectic phases are formed due to the water vapor

attack and Si diffusion at 1300°C (use temperature is generally limited to 1200°C)

Interface Si bond coat melting of

selected coating systems Si bond coat 1350°C BSAS+Si 1350°C

MulliteBSAS

Si

Interface reactions at 1300°C

17

Stability of Silicate Systems is Still of Great Concern

5 mm

— The phase partition in BSAS and ytterbium silicate systems observed

— Detrimental to temperature capability and recession resistance

Ytterbium mono- and di-silicates at

1300°C, 100 hours: stability issue

BSAS at 1482°C, 100 hr

Surface coating melting

18

Calcium-Magnesium-Alumino-Silicate (CMAS) Interactions

with EBCs – Ytterbium Mono-Silicate at 1500°C

CMAS attack:Yb2SiO5

CMAS - Yb2SiO5

19

The Yb2SiO5/Yb2Si2O7 EBC Delamination Crack

Propagation Tests under Laser Heat Flux Thermal

Gradient Cyclic Test Conditions ─ Penney-shaped crack with the initial size 1.5 mm in diameter, tested in air at

1350°C

─ Crack propagated from 1.5 mm to 7.5 mm 60, 1 hr cyclic testing

─ Possible SiO2 loss accelerated crack propagation

After 60 hr, 1 hr cyclic testing

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 70

kcera

TsurfaceTinterfaceTbackqthru

Therm

al c

onduct

ivit

y, W

/m-K

Tem

per

ature

, °C

Time, hours

Tinterface=1250°CTsurface=1350°C

Tback=1100°C

In-steam

20

Environmental Barrier Coating and High Heat Flux

Delaminations

Temperature, oC1467 oC 1315 oC

1066 oC

The FEM model

Crack Extension Force G as a function of time

for 2.0mm half delamination length and crack depth of 0.08mm

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.00 0.10 0.20 0.30 0.40 0.50

Time, sec

Cra

ck E

xte

nsio

n F

orc

e G

, J/m

2

4mm delamination length

32

28

Cra

ck e

xte

nsio

n d

rivin

g forc

e (

E=

~50G

Pa)

Cra

ck e

xte

nsio

n d

rivin

g forc

e (

E=

~200G

Pa)

24

20

16

12

8

4

0

Crack Extension Force G as a function of time

for 2.0mm half delamination length and crack depth of 0.08mm

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.00 0.10 0.20 0.30 0.40 0.50

Time, sec

Cra

ck E

xte

nsio

n F

orc

e G

, J/m

2

4mm delamination length

32

28

Cra

ck e

xte

nsio

n d

rivin

g forc

e (

E=

~50G

Pa)

Cra

ck e

xte

nsio

n d

rivin

g forc

e (

E=

~200G

Pa)

24

20

16

12

8

4

0

32

28

Cra

ck e

xte

nsio

n d

rivin

g forc

e (

E=

~50G

Pa)

Cra

ck e

xte

nsio

n d

rivin

g forc

e (

E=

~200G

Pa)

24

20

16

12

8

4

0

National Aeronautics and Space Administration

www.nasa.gov

Evolution of NASA EBC Technology for SiC/SiC Ceramic Matrix

Composites: Current State of the Art

21

Improved phase stability,

recession resistance of

top coat

Increased phase

stability and

toughness

Gen I (EPM)

1995-2000

Gen II (UEET)

2000-2004

Gen III (UEET)

2000-2005

Gen IV (FAP)

2005-2011

Gen V (FAP)

2009 - present

Engine

Components:

Combustor Combustor/

Vane

Combustor/

Vane

Vane/

Blade

- Vane/Blade EBCs

- Equivalent APS

combustor EBCs

Top Coat:

BSAS (APS)

RE2Si2O7 or

RE2SiO5 (APS)

- (Hf,Yb,Gd,Y) 2O3

- ZrO2/HfO2+RE

silicates

- ZrO2/HfO2+BSAS

(APS and EBPVD)

RE-HfO2-Alumino

silicate

(APS and/or 100% EB-

PVD)

RE-HfO2-X

advanced top coat

RE-HfO2-graded

Silica

(EB-PVD)

Interlayer:

--

--

RE-HfO2/ZrO2-

aluminosilicate

layered systems

Nanocomposite graded

oxide/silicate

Gen IV interlayer not

required (optional)

EBC: Mullite+ BSAS BSAS+Mullite RE silicates or RE-

Hf mullite

RE doped mullite-HfO2

or RE silicates

Multi-component RE

silicate systems

Bond Coat: Si Si

Oxide+Si bond

coat

HfO2-Si-X,

doped mullite/Si

SiC nanotube

Optimized Gen IV

HfO2-Si-X bond coat

2700°F bond coats

Thickness 10-15 mil 10-15 mil 15-20 mil 10 mil 5 mil

Surface T: Up to 2400°F 2400°F 3000°F 2700°F 3000°F

Bond Coat T: Limited to

2462°F

Limit to

2462°F

Limit to 2642°F Proven at 2600°F +;

Advancements

targeting 2700°F

2700°F (2013 goal)

Advanced compositions & processing for

thinner coatings, higher stability and

increased toughness

Challenges

overcome by

advancements:

22

NASA EBCs for ERA Program

• Focus on high technology readiness level (TRL), high stability multicomponent

HfO2-RE2O3-SiO2/RE2Si2-xO7-2x environmental barrier and advanced HfO2-Si bond

coat developments

• Processing optimization for improving coating density and composition control

robustness

• Develop advanced NASA high toughness, Alternating Composition Layered

Coating (ACLC) compositions and processing for low RE t’ low rare earth dopant

low k HfO2 and higher rare earth dopant silicates

• Optimize vapor deposition HfO2-Si based series bond coats, and second

generation 2700°F or 1500°C bond coat

- Achieving high toughness has been one of key emphases for NASA coating

technologies

23

NASA EBC for ERA Program - Continued • Focus on high technology readiness level (TRL), high stability multicomponent

HfO2 or ZrO2, HfO2-RE2O3-SiO2/RE2Si2-xO7-2x / environmental

barrier/environmental barrier seal coat, with advanced 2600°F+ HfO2-Si first gen

bond coat

– First and second Gen 2700°F/1500°C bond coats developed/evaluated

– Calcium Magnesium Alumino-Silicate (CMAS) resistance addressed

• Developed and evaluated EB-PVD/plasma spray hybrid combustor coatings

• Developed Triplex Pro and DVC based combustor EBC processing with Sulzer

Metco and Praxair

- Efforts in developing extensive new EBC coating powders with Sulzer

- Efforts in EBCs and DVM coatings in collaboration with Praxair

• Processing optimizations for improved plasma sprayed coating powders

composition controls and coating processing

• Developing 2000°F capable oxidation/fretting wear resistant coatings (Ti-Si-Cr/Ta-

CN systems and NiAl/NiAl+Cr/high toughness oxide/silicate systems)

• Optimizing/developing commercial HfO2-Si based series bond coats with Sulzer

24

Key Parameters in Boundary Layer Limited Transport

Recession Modeling

• SiO2(pure or in silicate solution) + 2 H2O(g) = Si(OH)4(g)

• Critical parameters to know are equilibrium constant for hydroxide

formation and activity of SiO2

2OHSiO

4OHSi

22Pa

PK

2OHSiO

)OH(Si

33.0

)OH(Si

5.0

)OH(Si)OH(Si

33.0

)OH(Si

5.0

22

4

4

44

4

PaKLTR

D

D

L664.0

LTR

PD

D

L664.0Flux

N. Jacobson, Silicate Activity Modeling and Measurements

N. Jacobson, “Mass Spectrometric Studies of Oxides” in Proceedings of the Workshop on Knudsen

Effusion Mass Spectrometry, April 23-25, 2012, Julich, Germany, ed. by N. S. Jacobson and T. Markus,

Electrochemical Society, Pennington, New Jersey, in press 2013.

25

High Pressure High Velocity SiC/SiC and EBC Recession

Studies Under Film Cooling Conditions

The CFD modeling of film cooled

CMC subelements, considering water

vapor fractions

Specimen recession and durability testing

under air cooled, heat flux conditions:

-1” and 2” discs, 600 psi cooling chamber

Film cooled CMC specimen Tested 10-hole film cooled CMC

specimen

surface backside

― Develop capabilities for determining SiC/SiC and EBC recession kinetics under very high

pressure and high velocity under impingement and impingement + film cooled test conditions

― Validating 3D CFD modeling capabilities, establishing recession models

Burner rig flow velocity

26

SiC/SiC CMC and EBC Recession Kinetics Determined for

CMCs-EBCs in High Pressure Bruner Rig and Laser

Steam Rig Testing

High temperature recession kinetics for film-cooled and

non-film cooled Gen II SiC/SiC CMCs

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Recession rate, mg/cm2-hr

Film cooled recession at 2400°F

Film cooled recession at 2100°F

Non-film cooling recession at 2100°F

Non-film cooling recession at 2400F

(model extrapolated to 300m/s gas velocity)

300 m/s, 16 atm

Examples of environmental barrier coating

recession in laboratory simulated turbine

engine conditions

― Determined recession under complex, and realistic simulated turbine conditions

1316°C

1316°C

1150°C

1150°C

27

Development and Processing of Directed Vapor Electron

Beam - Physical Vapor Deposition (EB-PVD) ─ NASA programs in supporting processing developments and improvements with Directed

Vapor Technologies International, Inc. • Multicomponent thermal and environmental barrier coating vapor processing

developments • High toughness erosion resistant turbine coatings • Affordable manufacture of environmental barrier coatings for turbine components

Directed Vapor Processing Systems

NASA HfO2-Si bond

coat on SiC/SiC

NASA Hybrid

EBC on SiC/SiC Advanced multi-component and multilayer turbine EBC systems

28

Development and Processing of Directed Vapor Electron

Beam - Physical Vapor Deposition (EB-PVD) - cONTINUED ─ NASA multicomponent Rare Earth (RE) Silicate /HfO2-RE-Silicate coatings with distinct vapor

pressures; advanced HfO2-Si processing HfO2-Si with co-deposition

HfO2-Si bond coat

Hf-RE-Silicate

SiO2 grading

Hf-RE

Silicate

RE

Silicate+X

Surface

Type II HfO2-Si bond coat Type II HfO2-Si bond coat HfO2-Si bond coat co-depositon

29

Plasma Sprayed-Physical Vapor Deposition (PS-PVD)

Processing of Environmental Barrier Coatings ─ NASA PS-PVD and PS-TF coating processing using Sulzer newly developed technology

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

• High flexibility coating processing – PVD - splat coating processing at lo pressure (at ~1 torr)

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

• Emphasis on fundamental process and powder composition developments for advanced

EBC compositions

(a) Without powder

(b) With initial powder feeding

(b) Full powder feeding

High enthalpy plasma vapor stream for efficient and

complex thin film coating processing

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

NASA hybrid PS-PVD coater system – A flagship

plasma Spray coating system

100 kW power, 1 torr operation pressure

30

Plasma Sprayed-Physical Vapor Deposition (PS-PVD)

Processing of Environmental Barrier Coatings - Continued

Vapor NASA low k ZrO2-Y2O3

coating Splat/partial vapor Yb2Si2O7/

Yb2SiO5

─ Demonstrated vapor-like coating deposition for thermal barrier and environmental

barrier coatings • Advanced powders developed with Sulzer under NASA programs using NASA

specifications

─ Properties and durability being evaluated and demonstrated • High temperature and stability (thermodynamically) processing

• Demonstrated erosion resistant, dense high stability thermal and environmental barrier

coatings for turbine airfoils

31

The NASA HfO2+Si Bond Coat Showed Significantly

Improved Temperature Capability as Compared to Silicon

─ Higher stability demonstrated in early testing even after 1450ºC+ high

temperature and testing

Cross-section, Hot-pressed HfO2-50wt%Si

on CMC, 1350°C tested

0

1 104

2 104

3 104

4 104

5 104

6 104

10 20 30 40 50 60 70 80

HfO2-25wt%Si-1350°C

HfO2-50wt%Si-1350°C

HfO2-75wt%Si-1400°C

HfO2SiHfSiO4

-1 104

0

1 104

2 104

3 104

4 104

5 104

6 104

Re

lative

In

ten

sity

Re

lative

In

ten

sity

Diffraction angle, 2

Cross-section, Type II EB-PVD HfO2-Si

bond coat, 1500°C, 200hr tested

32

High Pressure Burner Rig HfO2+Si Bond Coat Stability and

Recession Testing

─ The Bond Coat showed good stability

-20

-15

-10

-5

0

5

0 5 10 15 20 25 30 35

EB-PVD HfO2-Si

Wei

gh

t ch

ang

e, m

g/c

m2

Time, hours

1372C, combustion gas 20 m/s; 16 atm

33

Plasma Spray HfO2+Si Bond Coats

─ Commercial grade HfO2-Si bond coats being developed in collaboration with Sulzer Metco

─ The initial versions high temperature bond coat tested for 100 hr in air at up to 1500°C in

NASA laser high heat flux rig

─ High temperature strengths of the bond coat also observed

Scale up and down-selections of

commercial source NASA HfO2-

Si EBC Bond Coating Powders

AE 10219 bond coated

CMC specimen on test rig

after heat flux testing

0

50

100

150

200

HfO2-Si - 1300C

HfO2-Si - 1400C

t' HfO2 - 1400C

t' HfO2+ytterbium di-silicate - 1400C

Ytterbium di-silicate - 1400C

Str

eng

th,

MP

a

Selected coating materials

34

0

50

100

150

200

250 0

2

0 200 400 1000 1200 1400 1600

Flexural strength, MPa

Deflection, mm

Fle

xu

ral

stre

ngth

, M

Pa

Def

lect

ion

, m

mTemperature, °C

─ The initial versions high temperature bond coat tested for 100 hr in air at up to 1500°C

─ High strength observed up to 1400°C flexural testing

─ Extensive creep deformation in 1500°C strength tests, but showing resistance to fracture

Flexural Strength Evaluation of Monolithic HfO2-Si Bond

Coat Materials

Two HfO2-Si bond coat

material specimens tested

at 1500°C

35

− 1500°C capable RESiO+X(Ta, Al, Hf, Zr …) EBC bond coat

compositions and related composite coatings developed for

combustor and turbine airfoil applications

− The bond coat systems demonstrated durability in the laser high

heat flux rig in air and steam thermal gradient cyclic testing

− The bond coatings also tested in thermal gradient mechanical

fatigue and creep rupture conditions

Advanced Bond Coats for Turbine Airfoil and Combustor

EBCs Developed – NASA Provisional Patent

High heat flux cyclic rig tested Zr/Hf-RE-Si series

EBC bond coats on the bond coated woven

SiC/SiC CMCs at 1450°C in air and full steam

environments

RESi-Hf, 100 hr RESi+Al, 50 hr RESi+Al, 50hr

100% steam

Steam heat flux test rig of

the bond coat

Processed Subelement

Selected

Composition Design

of Experiment

Furnace Cyclic Test

Series 1500°C, in air,

Demonstrated 500hr

durability

RE-Si-Hf

RE-Si/EBC

36

Advanced Bond Coats for Turbine Airfoil and Combustor

EBCs being Developed - Continued

An oxidized

bond coat

after 1500°C

100 h creep

testing

− 1500°C capable RESiO+X(Ta, Al, Hf, Zr …) EBC bond

coat compositions and related composite coatings

− Oxidation kinetics being studies using TGA in flowing O2

− Parabolic or pseudo-parabolic oxidation behavior

observed

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

65 70 75 80 85

RESi(O) series-4RESi(O) series-5RESi(O) series-6RESi(O) series-7RESi(O) series-8RESi(O) series-9

Kp,

mg

4/c

m2-s

ec

Silicon composition, at%

0

100

200

300

400

500

600

0 20 40 60 80 100 120

RESi(O) series-4RESi(O) series-5RESi(O) series-6RESi(O) series-7RESi(O) series-8RESi(O) series-9

Fle

ura

l st

reng

th, M

Pa

Temperature, °C

1500°C in O2

37

Some Advanced EBC Top Coat Material Strength

Evaluations

0

50

100

150

200

250

300

350

0 200 400 600 800 1000 1200 1400 1600

HfO2-Sit' HfO2HfO2+10wt%Yb2SiOxHfO2+80wt%Yb2SiOxZr-RE-Si-OHfO2Y2Si2O7Yb2Si2O5RE SilicateHf-RE-Si-O

Fle

ura

l st

reng

th, M

Pa

Temperature, °C

− Focus on the development high strength and high toughness EBC materials

− Provide property database for design and modeling

38

NASA Turbine Environmental Barrier Coating Testing

Developments ─ Advanced EBC top coats tested in coupons under laser heat flux cyclic rigs up 1700°C

─ Coated subelements coating tested up 1500°C under laser thermal gradient for 200 hr

─ EBC systems show high stability in High Pressure Burner Rig Tests

─ Thermal conductivity of 1.2 W/m-K for optimized turbine coatings

High pressure burner rig, 16 atm, 31 hr 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

400

800

1200

1600

0 10 20 30 40 50 60

kcera

Tsurface

Tinterface

Tback

qthru

EB

C T

herm

al

condu

cti

vit

y, W

/m-K

Tem

pera

ture

, °C

Time, hours

Tsurface=~1482°C

Tinterface=1256°C

Tback=1068°C

Hyper-Therm TECVI Woven SiC/SiC

EBC ID 23_3.5.3 on Prepreg MI1847-01-038

39

NASA Turbine Environmental Barrier Coating Testing

Developments

─ High stability systems (Yb,Gd,Y+Hf) silicates, processed and down selected

─ Processing optimization also emphasized

Turbine EBCs: High pressure burner rig tested at 10 atm, 2650°F

HfO2-Si bond coat

High stability EBC

silicate top coat

High stability EBC

40

Advanced EBC developments – Some Hybrid APS-PVD

Systems and Qualification Tests • EB-PVD HfO2-RE2O2 (Silicate) top coat EBC with

plasma-spayed multi-component advanced silicate

sublayer EBC/HfO2-Si bond coat systems

• Low thermal conductivity ranging 1.0 - 1.7 W/m-K

• Demonstrated high pressure environmental stability

at 2600-2650°F, 12-20 atm in the high pressure

burner rig

2” diameter ND3

EBC/SiC/SiC

specimen after

testing in the high

pressure burner rig

At 2600°F

High pressure burner rig tested new ND series Hybrid

EBC systems coated on 2” diameter Gen II Prepreg

SiC/SiC CMCs

ND2 ND6 ND7

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20

ND0 HfRE-RESilicate EBC 7.4 on Prepreg SiC/SiCND2 HfRE-RESilicate EBC 7.2 on Prepreg SiC/SiCND3 HfRE-RESilicate EBC 7.2 on Prepreg SiC/SiCND6 HfRE(Si)-RESilicate EBC 7.2 on Prepreg SiC/SiCND7 HfRE(Si)-RESilicate EBC 7.2 on Prepreg SiC/SiC

Th

erm

al c

ond

uct

ivit

y,

W/m

-K

Time, hours

EBC test temperture 2700°F, heat flux 120 W/cm2

Laser rig testing at 2700°F (1482°C)

41

Thermal Gradient Tensile Creep Rupture Testing of Advanced

Turbine Environmental Barrier Coating SiC/SiC CMCs

─ Advanced high stability multi-component hafnia-rare earth silicate based turbine

environmental barrier coatings being successfully tested for 1000 hr creep rupture

─ EBC-CMC fatigue and environmental interaction is being emphasized

Cooling

shower head

jets

Test specimen

High

temperature

extensometer

Laser beam

delivery optic

system

EBC coated tensile specimen

Tback surface

Tsurface

EBC Thickness

Substrate thickness

ε ela

stic

+ε c

reep

oC

Through Thickness Crack Spacing 2W

Delamination Crack Length 2a

Opening StressShear Stress Temperature

FEM models for delamination cracking under thermal

gradient and tensile creep loading

To

tal

stra

in,

%

0.0

0.5

1.0

1.5

0 200 400 600 800 1000 1200

Time, hours

Gen II CMC with advanced EBC

Tested 20 ksi, 1316°C

Gen II CMC-uncoated

Tested at 20 ksi, 1316°C

Gen II CMC uncoated

Tested at 15 ksi, 1316°C

Typical premature

failure

Tsurface = 1482°C

Tinterface= 1371°C

TCMC back=1271°C

Gen II CMC with advanced EBC

Tested at 15 ksi & heat flux

Tsurface = 1510ºC

Tinterface = 1350ºC

TCMC back = 1232ºC

Gen II CMC with advanced EBC

Tested at 20 ksi & heat flux

42

─ Advanced environmental barrier coatings – Prepreg CMC systems demonstrated long-term

EBC-CMC system creep rupture capability at stress level up to 20 ksi at TEBC 2700°F, TCMC

interface ~2500°F

─ The HfO2-Si bond coat showed excellent durability

Thermal Gradient Fatigue-Creep Testing of Advanced

Turbine Environmental Barrier Coating SiC/SiC CMCs -

Continued

Hybrid EBCs on Gen II CMC after 100 hr

low cycle creep fatigue testing

EBCs on Gen II CMC after 1000 hr fatigue

testing

43

EBC-CMC Thermal Gradient Creep Rupture and

Delamination Modeling • An equivalent stress model is established for EBC multicrack stress intensity modeling:

emphasize creep, thermal gradient and stress rupture interactions

• Benchmark failure modes established in EBC systems:

0

5

10

15

20

25

30

35

40

0 0.2 0.4 0.6 0.8 1

Multilayer EBC Delamination Driving Force

300 micron coating, 0.06% creep strains380 micron coating, 0.06% creep strains300 micron coating, 0.15% Creep strain

Ten

sile

str

ain

induce

d c

oat

ing d

elam

inat

ion

ener

gy r

elea

se r

ate,

J/m

2

Nomalzied crack length, a/W

1220

1230

1240

1250

1260

1270

1280

1290

1300

1310

1320

1330

1340

1350

1360

-75

-50

-25

0

25

50

75

100

125

150

175

200

225

250

275

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Tem

pe

rature

( C )

Axi

al S

tre

ss (

MP

a)

Through thickness distance (mm)

Through the thickness axial stress profile at different time

Thermal-Stress

0.0001

0.1063

4.1157

98.654

258.65

518.65

758.65

1000

Temperature

Stress gradients in Prepreg SiC/SiC CMC

substrates under thermal gradient + mechanical

creep loading

EBC top coat

EBC

SiC/SiC CMC

EBC bond coat EBC bond coat

SiC/SiC CMC

Composite EBC

EBC

CM

C l

ay

er

1

CM

C l

ay

er

2

CM

C l

ay

er

i

EB

C

CM

C l

ay

er

1: e,

s1,

T1

CM

C l

ay

er

2: e,

s2,

T2

CM

C l

ay

er

i:

, s

i, T

1i

EB

C: e E

BC, s

EB

C,

TE

BC

44

Advanced Ballistic Impact Resistant Turbine EBC Systems

─ Advanced EBCs on par with best TBCs in impact resistance

ND2

ND3

ND6

SUP-ERA 7.4

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 0.5 1.0 1.5 2.0 2.5

7YSZ and low k TBCs

ZrRETT

ATES series

ND2

ND3

ND6

ND7

SUP-ERA7.4 EBC

t'-ZrO2/NASA EBC

Cubic low k ZrO2 k-NASA EBC

Spal

led

are

a, c

m2

Energy, J

150 200 500250 350 400 450300

Projectile velocity, m/s

NASA SUP-ERA 7.4 EBC

ND6 NASA EBC

t'/ NASA EBCND7 NASA EBC

Spalled

RE

With Si

45

The SiC/SiC CMC Turbine Airfoils Successfully Tested for Rig

Durability in NASA High Pressure Burner Rig

EBC coated turbine vane subcomponents tested in rig simulated engine

environments (up to 240 m/s gas velocity, 10 atm), reaching TRL of 5

Coated CVI SiC/SiC vane after 31 hour

testing at 2500°F+ coating temperature

Coated Prepreg SiC/SiC vane after 21

hour testing at 2500°F

Coated Prepreg

SiC/SiC vane tested 70

hour testing at 2650°F

46

The First Set Prepreg SiC/SiC CMC Combustor Liner Successfully

Tested for Rig Durability in NASA High Pressure Burner Rig (First

Inner Liner Processed at Sulzer with Triplex Pro)

1000

1200

1400

1600

1800

2000

2200

2400

0.040 0.045 0.050 0.055 0.060 0.065 0.070 0.075 0.080 0.085 0.090

Ad

iab

atic

Fla

me

Te

mp

era

ture

, C

Fuel to Air Ratio

Ideal Flame Temperature Calculation - Chemical Equilibrium Analysis Codes (CEA)-II

Hot streaks with

possible gas

temperature over

2000°C, with

minimum back

cooling

Swirl jet flows

Some minor coating spalling at hot

streak impingement

─ Tested pressures at 500 psi external for outliner, and up to 220 psi inner liners in the

combustion chamber (16 atm), accumulated 250 hours in the high pressure burner rig

─ Average gas temperatures at 3000°F (1650°C) based on CEA calculations, the liner EBCs

tested at 2500°F (1371°C) with heat fluxes 20-35 W/cm2, and the CMC liner component at

1800-2100°F (~1000-1100°C)

47

Summary • Durable EBCs are critical to emerging SiC/SiC CMC component technologies

─ The EBC development built on a solid foundation from past experience

─ Advanced EBC processing and testing capabilities significantly improved, helping more

advanced coatings to be realized for complex turbine components

─ Developed new series of EBC and bond coat compositions for meeting SiC/SiC CMC

component performance requirements and long-term durability, establishing expanded

scientific research areas

─ Better understood the coating failure mechanisms, and helping developing coating

property databases and life models

─ Emphasized thin coating turbine and combustor EBC coating configurations,

demonstrated component EBC technologies in simulated engine environments

─ Continue the coating composition and architecture optimization and developments to

achieve 1482-1650°C capability, targeting uncooled and highly loaded components

• The component and subelement testing and modeling

─ Understand EBC-CMC degradation and life prediction under complex thermal cycling,

stress rupture/creep, fatigue, and environmental integrations

48

Future Directions and Opportunities • High stability, thin coating system development is a high priority

– Emphasize advanced processing and composite coating systems

– Reduce recession rates, improve the temperature stability and environment

resistance

– Significantly improve the interface stability and reduce reactivity

– Low thermal conductivity

• Coatings with significantly improved thermal and mechanical load

capability is required

– Significantly improve the coating strength and toughness, and impact

resistance

– Design and demonstrate long-term high heat flux cyclic stability

– Develop and demonstrate high temperature (thermal gradient) erosion-

impact testing up to 2700°F

• Materials and component system integration

– Optimize and test coatings with components and SiC/SiC substrates

– Enhance functionality with embedded sensing and self-healing capability

– Integrate with virtue sensors and real time life predictions

• Laboratory simulated high heat flux stress, environment testing and life

prediction methodology development

49

Acknowledgements

• The work was supported by NASA Environmentally Responsible Aviation (ERA)

Project and Fundamental Aeronautics Program (FAP) Aeronautical Sciences Project

NASA colleagues: Dennis S. Fox, James L. Smialek, Bryan Harder, Nate Jacobson, Louis Ghosn, Robert A. Miller,

James DiCarlo, Janet Hurst, Martha H. Jaskowiak, Mike Halbig, Narottam Bansal, Ram Bhatt, Nadia Ahlborg,

Matt Appleby

NASA Branches include: Durability and Protective Coatings Branch (Chief: Joyce A. Dever), Ceramic Branch (Chief:

Joseph E. Grady), and Life Prediction Branch (Chief: Steve M. Arnold)

Collaborators include:

Sulzer Metco (US) - Mitch Dorfman; Chis Dambra

Directed Vapor Technologies, International – Derek Hass and Balvinder Gogia

Praxair Surface Technologies – John Anderson and Li Li

Southwest Research Institute – Ronghua Wei

General Electric Aviation, Rolls Royce, Pratt & Whitney, and Honeywell Engines