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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