Development Status and Performance Comparisons of Environmental Barrier Coating Systems for SiCSiC Ceramic Matrix Composites

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

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

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 blade 3200°F (T41) Gas TBC Bond coat Metal blade 3200°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 TBCs 2700-3000°F EBCs Thin turbine coating development 2200°F TBCs 2400°F CMCs 2700°F CMCs

Fundamental Recession Issues of CMCs and EBCs

SiC Wt. L oss (m g/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/(Ptotal)1/2 Combustion gas

SiO₂+ 2H₂O(g) = Si(OH)₄(g)

Combustion gas Cooling air (a) (b) 0.01 0.1 1 AS800 SN282 SiC/SIC CMC La 2Hf2O7 HfO 2 (doped) RE-Hf-luminosilicates BSAS S pe ci fi c w ei ght c ha n g e, m g/ cm 2 -h

Supersonics EBC stability development goal - 2005 1300

Temperature, °C 1400

1500 1200

1600

SiC/SiC under high velocity

Rare earth silicates

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

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

Advanced Environmental Barrier Coating Systems:

Coating Material System Developments and Architecture

•

High-stability multi-component ZrO

₂

/HfO

₂

, 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, HfO

₂

-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 HfO₂composites Doped mullite

with ACLC (Hf rich bands)

Doped HfO₂+Si and mullite/Si composite bond coat (High temperature capable with self-healing)

Increased SiO₂activity

Increased dopant RE/Transition metal concentrations & increased Al/Si ratio

Advanced Environmental Barrier Coating Systems

200

m

m

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

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

m

m

Early generation hybrid environmental

barrier coatings systems processed

with combined Plasma Spray and

EB-PVD processing

EB-PVD Advanced HfO

₂

Plasma spray ytterbium silicate

EBC Processing using Plasma Spray and EB-PVD

HfO₂-Si bond coat

Oerlikon Metco Triplex Processed Advanced EBCs

HfO₂-Si bond coat

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 coating

Splat/partial vapor Yb₂Si₂O₇

10 mm

HfO₂-Si bond coat

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 tanc e from s urfac e Heat flux

Turbine: 450°F across 100 microns Combustor:1250°F across 400 microns

Test rig

Real-Time Thermal Conductivity Measurements

and Damage Monitoring

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 1, 1500°C EBC System 2, 1500°C EBC System 3, 1500°C EBC System 4, 1500°C EBC System 5, 1500°C EBC System 6, 1500°C

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

T her ma l con duct ivi ty, W /m-K T her m al c on duc ti v ity, W /m-K Failure Failure Failure

─ 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

Thermal Conductivity of PS-PVD Yb

₂

Si

₂

O

₇

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 Yb2Si2-xO7-x System 2 Yb2Si2-xO7-x System 3 Yb2Si2-xO7-x System 4 Yb2Si2-xO7-x System 5 Yb2Si2-xO7-x System 6 Yb2Si2-xO7-x System 7 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 Therm al cond uctivity, 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

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 Tsurface Tinterface Tback qthru Th er ma l cond u ct ivit y , W /m-K T emp erat u re , °C Time, hours Tinterface=1120°C Tsurface=1400°C Tback=920°C

Three layer HfO₂-ytterbium silicate-Si completed 50hr laser heat flux thermal ─ 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

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

m

m

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°C Tinterface = 1420°C Tback=1310°C T h ermal con d uc ti v it y , W /m-K T e mpe ratu re , °C Time, hours

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)+Yb2Si2O7/Yb2SiO5 50:50 Multi-component HfO2(t',m)+Yb2Si2O7/Yb2SiO5 70:30 Multi-component HfO2(t',m)

-

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

EB-PVD Composite Environmental Barrier Coatings –

CMAS Reaction Tested

_{HfO2-Si bond coat}

EB-PVD Processed EBCs: alternating HfO

₂

-rich and ytterbium silicate layer

systems for CMAS and impact resistance

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

Bond Coats

SiC

RESi(O)

RE

₂

Si

₂

O

_7-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

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 T ot al s tr ai n, % 0.0 0.2 0.4 0.6 0.8 1.0 0 200 400 600 800 1000 1200 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 ksi Tsurface =~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

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 HfO

₂

-rare earth silicate

and GdYbSi (controlled oxygen activity) bond coat tested at T

_EBC-surface

1537°C,

T

_{bond coat}

1480°C, T

_{back 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

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 Ma ximum s tre ss , MP a Fatigue cycles

High temperature strength data

Fatigue or creep hot time, hours

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

2550F 2700F

•

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

Summary and Conclusions

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

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)