1

Development of Advanced Environmental Barrier Coatings for

SiC/SiC Ceramic Matrix Composites:

Path toward 2700°F Temperature Capability and Beyond

Dongming Zhu, Bryan Harder, Janet B. Hurst, Brian Good, Gustavo Costa,

Ramakrishna Bhatt and Dennis S. Fox

Materials and Structures Division

NASA Glenn Research Center

Cleveland, Ohio 44135, USA

41st Annual Conference on Composites, Materials, and Structures

Cocoa Beach, Florida

January 23-27, 2017

https://ntrs.nasa.gov/search.jsp?R=20170005218 2018-07-02T12:58:27+00:00Z

2

Durable Environmental Barrier Coating Systems for Ceramic

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

Light-Weight Propulsion, and Extreme Environment Material Systems

— NASA Environmental barrier coatings (EBCs) development objectives

• Help achieve future engine temperature and performance goals

• Ensure system durability – towards prime reliant coatings and material systems

• Establish database, design tools and coating lifing methodologies

• Improve technology readiness

Fixed Wing Subsonic and Supersonics Aircraft:

- Transformational Tools and Technologies ProjectEntry, Descending and Landing: Ultra High Ceramics

and Coatings (UHTCC) - NASA CIF Project

3

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

• 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) turbine and CMC combustor coatings

- Recession: <5 mg/cm2 per 1000 h

- Coating and component strength requirements: 15-30 ksi, or 100- 207 MPa

- Resistance to Calcium Magnesium Alumino-Silicate (CMAS), impact and erosion

- Demonstrate feasibility towards Ultra High Temperature and Multifunctional Ceramics – Coating Systems: improved environmental stability and mechanical stability

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

44

Outline

• Advanced EBC and Rare Earth – Silicon based 2700°F+ capable bond coat developments

- Material systems

- Oxidation resistance

- Cyclic and thermomecahnical durability

- Some bench mark durability tests for 2700°F EBC systems

• Ultra High Temperature and Multifunctional Ceramic Matrix Composite –Coating Systems for Light-Weight Space and Aero Systems

- HfCN based system with Si and RE dopant concepts

- Develop HfO2 – Si based coatings for improved oxidation resistance

• Summary and conclusion

5

Environmental Barrier Coating Development: Challenges

and Limitations

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

long-term durability

─ Advanced EBCs also require 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

─ Also possibly developed to Ultra High Temperature Ceramics applications

66

Advanced High Temperature and 2700°F+ Bond Coat

Development

NASA advanced EBC Development: • Advanced compositions ensuring environmental and mechanical

stability• Bond coat systems for prime reliant EBCs; capable of self-healing

High strength, high

stability reinforced

composites: HfO2-Si

and a series of Oxide-

Si systems

HfO2-Si based and

minor alloyed systems

for improved strength

and stability, e.g., rare

earth dopants

Advanced 2700°F

bond coat systems:

RE-Si based systems

Advanced 2700°F bond

coat systems: RE-Si based

Systems, grain boundary

engineering designs and/or

composite systems

HfO2-Si systems Advanced 2700°F+ Rare Earth - Si Bond Coat systems

Rare Earth – Si + Hf coating systems

Hf – Rare Earth – Si coating systems

Temperature capability increase

7

NASA EBC Bond Coats for Airfoil and Combustor EBCs– Patent Application 13/923,450 PCT/US13/46946, 2012

– Advanced systems developed and processed to improve Technology Readiness Levels (TRL)

– Composition ranges studied mostly from 50 – 80 atomic% silicon– Silicon and dopant composition being optimized for 2700°F EBC applications

YSi YbGdYSi GdYSi

ZrSi+Y YbGdYSi GdYSi

ZrSi+Y YbGdYSi GdYSi

ZrSi+Ta YbGdYSi GdYSi

ZrSi+Ta YbGdSi GdYSi-X

HfSi + Si YbGdSi GdYSi-X

HfSi + YSi YbGdSi

HfSi+Ysi+Si YbGdSi

YbSi YbGdSi

HfSi + YbSi

YbSi

GdYbSi(Hf)

YYbGdSi(Hf) YbYSi

YbHfSi

YbHfSi

YbHfSi

YbHfSi

YbHfSi

YbSi

HfO2-Si;

REHfSi

GdYSi

GdYbSi

GdYb-LuSi

NdYbSi

HfO2-Si

YSi+RESilicate

YSi+Hf-RESilicate

Hf-RESilicate

Used in ERA components as part of bond coat system

Hf-RE-Al-Silicate Used in ERA components as part of bond coat system

PVD-CVD EB-PVD APS*

REHfSi

FurnaceLaser/C

VD/PVD

Process and

composition

transitions

APS*: or plasma spray related

processing methods

8

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

60 65 70 75 80 85

RESi(O)RESi(O)RESi(O)

RESi(O)RESi(O)

RESi(O)

RESi(O)

RESi(O)RESi(O)RESi(O)

RESi(O)

RESi(O)

HfO2-SiHfO2-Si

Kp, m

g2/c

m4-s

ec

Silicon composition, at%S

ilic

on c

on

cen

trat

ion

, at

%

8

Oxidation Kinetics and Furnace Cyclic Durability of RESi

EBC Bond Coats for 2700°F SiC/SiC CMC Systems

Oxidation kineticsFCT life, Testing in Air at 1500°C, 1 hr cycles

SiC

RESi(O)

RE2Si2O7-x

Transition region

between Si-rich

and silicate regions

40 mm

Cross-section TGA tested specimen

0

1

2

3

4

5

0 100 200 300 400 500 600

Specific weight gain, mg2/cm4Sp

ecif

ic w

eig

ht

gai

n,

mg

2/c

m4

Time, hours

YGdSi bond coat on SiC/SiC, 1500°C

1500°C (2700°F+) capable RESiO+X series EBC bond coat compositions developed for turbine engine

coatings

Oxidation kinetics in flowing O2 showed parabolic or pseudo-parabolic oxidation behavior at high

temperatures

Some early multi-component systems showed significantly improved furnace cyclic durability at 1500°C

9

Microstructures of the Advanced EBCs after the Oxidation

Tests

– RE-Si system: forming RE silicate “scales”, fully compatible with EBCs

– Reaction and oxidation mechanisms are being further studied, particularly RE

containing SiO2 – rich phase stability

– Further process improvements can help improve the oxidation resistance and

durability

9

EBC layer 1

EBC layer 2

EBC bond coat

SiC/SiC CMC

Cross-section micrograph of

YbGdSi(O) tested at 1500°C, 500hr

EBC bond coat“scales”

Yb,Gd,Y silicate EBC Layer 2

Yb,Gd silicate scale

1010

Microstructures of Furnace Cyclic Tested GdYbSi(O) EBC

Systems— Cyclic tested cross-sections of PVD processed YbGdSi(O) bond coat

— Self-grown rare earth silicate EBCs and with some RE-containing SiO2 rich phase separations

— Relatively good coating adhesion and cyclic durability

1500°C, in air, 500, 1 hr cycles

AB

B

A

Composition (mol%) spectrum Area #1

SiO2 67.98

Gd2O3 11.95

Yb2O3 20.07

Composition (mol%) spectrum Area #2

SiO2 66.03

Gd2O3 10.07

Yb2O3 23.9

- Complex coating architectures

after the testing

- Designed with EBC like

compositions – Self-grown

EBCs

1111

Microstructures of Cyclic Tested GdYbSi(O) EBC

Systems- Continued

1500°C, in air, 500, 1 hr cycles

Outlined area SpotComposition (mol%)

SiO2 66.72

Gd2O3 8.62

Yb2O3 24.66

Composition (mol%)

SiO2 96.15

Gd2O3 1.2

Yb2O3 2.64

— Cyclic tested cross-sections of PVD processed YbGdSi(O) bond coat

— Self-grown rare earth silicate EBCs and with some RE-containing SiO2 rich phase separations

— Relatively good coating adhesion and cyclic durability

12

0

20

40

60

80

100

0

20

40

60

80

100

0 10 20 30 40 50

Si

O

Sil

ico

n c

oncen

trati

on,

at%

Oxyg

en c

on

cen

trat

ion,

at%

Hafnium concentration, at%

12

HfO2-Si Bond Coats Processing and Composition

Optimizations─ EB-PVD HfO2-Si bond coat process and composition extensively studied

─ Achieving lower oxygen activity, lower silicon content, with robust processing

─ Coating systems demonstrated durability in various lab tests

─ Potential systems for using as “scales and coatings” of UHTCC

1313

HfO2-Si EBC Bond Coat Temperature Capability Tested

─ HfO2-Si bond coat tested at up to 1560°C +, 50 h

─ Higher temperature region had

HfO2-Si At%

O 26.08

Si 49.10

Hf 24.82

Total 100.00

HfO2-Si surfaceHf

HfHfHfHf

O

Low oxygen content

HfO2-Si surface

HfO2-Si At%

O 50-56

Si 4-10

Hf 30-40

Total 100.00

Low oxygen content

14

Advanced RE-Si Based EBC Bond Coats: Controlled

Oxygen Activities, Dopant Additions– Advanced compositions improve high temperature stability and environmental resistance

– Refined grain structures observed for hafnium-doped systems after 500 h furnace cyclic tests

YbSi-YbSi(O) EBC bond coat, 1500°C cyclic tested YbSi-YbSi(O)+Hf EBC bond coat, 1500°C cyclic tested

15

Advanced RE-Si Based EBC Bond Coats: Controlled

Oxygen Activities, Dopant Additions– Oxidation kinetics comparisons for various 2700°F coating systems

– The PVD processed REHfSi shown to have lower oxidation rates

-6.5

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

0.0005 0.00055 0.0006 0.00065 0.0007 0.00075 0.0008

YbGdSiLuGdSiLuGdSi/with PVD YbGdSiHfO2-SiYbGdHfSi

Ln

Kp

, m

g2/c

m2-h

1/T, K-1

Activation energy 110.6 kJ/mol

Activation energy 136.5 kJ/mol

Activation energy 54 kJ/mol

0

5

10

15

20

0 100 200 300 400 500 600

YbGdLuSi

YbGdHfSiS

pec

ific

wei

ght

gai

n, m

g2/c

m4

Time, hours

YGdSi-series bond coat on SiC/SiC, 1500°C

16

Thermal Gradient Tensile Creep Rupture Testing of Advanced

Turbine Environmental Barrier Coating SiC/SiC CMCs

- Some Benchmark Tests─ Advanced multi-component hafnia-rare earth silicate based turbine environmental barrier

coatings being tested for up to 1150 h creep rupture

─ Helped understand EBC-CMC creep, fatigue and environmental interactions, and modeling

Cooling

shower head

jets

Test specimen

High

temperature

extensometer

Laser beam

delivery optic

system

EBC coated tensile specimen

1

Tota

l st

rain

, %

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 = 2700°F

Tinterface= 2500°F

TCMC back=2320°F

Gen II CMC with advanced EBC

Tested at 15 ksi & heat flux

Tsurface = 2750ºF

Tinterface = 2450ºF

TCMC back = 2250ºC

Gen II CMC with advanced EBC

Tested at 20 ksi & heat flux

2400 F

2400 F

2250 F2400 F

EBCs on Gen II CMC after 1000 h fatigue testing

17

Laser Thermomechanical Creep - Fatigue Tests of

Advanced 2700°F+ EBC Systems

- APS, PVD and EB-PVD processed 2700°F bond coats and EBCs on SiC/SiC

CMC: focus on creep, fatigue high heat flux testing at temperatures of 1316-

1482°C+ (2400-2700°F+) – selected Examples

Creep rate 7.1x10 -6 1/s

EB-PVD Rare Earth Silicate EBC/YbGdYSi bond coat on Hyper Therm CVI-MI

TEBC surface 2850-3000°F (1600-1650°C)

Tcmc back at ~2600°F (1426°C)

D. Zhu, “Advanced Environmental Barrier Coatings for SiC/SiC Ceramic Matrix Composite Turbine

Components”, Engine Ceramics – Current Status and Future Prospects, pp 187-202, 2016

18

Laser Thermomechanical Creep - Fatigue Tests of

Advanced 2700°F+ EBC Systems - Continued

- APS, PVD and EB-PVD processed 2700°F bond coats and EBCs on SiC/SiC

CMC: focus on creep, fatigue high heat flux testing at temperatures of 1316-

1482°C+ (2400-2700°F+) – Selected Examples

Fatigue Tested (furnace)

PVD GdYSi(O) coated on CVI-MI SiC/SiC

1316°C, 10ksi, 1000 h fatigue (3 Hz, R=0.05)

Air Plasma Sprayed APS YSi+Hf-RESilicate

EBC Bond Coat series on CVI-MI SiC/SiC

1400°C,at 10 ksi, 400 hr

Creep and Fatigue Tests with CMAS

EB-PVD (HfRE2Si2-xO7-x EBC/GdYbSi(O) bond

coat on CVI-MI SiC/SiC (with CMAS)

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

EB-PVD (RE2Si2-xO7-x EBC/HfO2-Si bond coat on

3D CVI+PIP SiC/SiC (1482°C, 10ksi, 300 h

SPLCF fatigue at 3 Hz, R=0.5; furnace tested)

Fatigue Tested

19

Laser Thermomechanical Creep - Fatigue Tests of

Advanced 2700°F+ EBC Systems - Continued- Benchmark fatigue testing at 2700°F of coating

system

- Also demonstrating laser steam rig 500 hr at

laser rig tests at 2700°F+ EBC temperatures

- Development towards 3000°F+ thin coatings

Front with EBC and bond coat

Back with bond coat only

After testing

3hz fatigue testing at 10 ksi loading

Completed 500 hr testing in heat flux rig

with steam

EBC

Fast strength tested after fatigue testing

Bond coat

20

Ultra High Temperature and Multifunctional Ceramic Matrix

Composite – Coating Systems for Light-Weight Space and Aero

Systems

– Develop Ultra High Temperature Ceramics and Coatings (UHTCC) based on HfCN and

HfTaCN

– Focused on Hf-RE-Si-O-(CN) protective scales or coatings to improve oxidation resistance

– Evaluate and improve mechanical properties

– Incorporated atomistic modeling, and thermodynamic measurements and modeling

– Initiated the system testing and coating developments

Surface

HfCN based composites:

matrix

CO2 laser heat flux

Nanofiber reinforced composites

HfCN layer

NASA Hf(RESi)CN(O)

– Qi-June Hong and Axel van de Walle, “Prediction of the material with highest

known melting point from ab initio molecular dynamics calculations”, Physical

Review B92, 020104-1 - 020104-6 (R) (2015).

21

Ultra High Temperature and Multifunctional Ceramic Matrix

Composite – Coating Systems for Light-Weight Space and Aero

Systems - continued– Downselected initial HfC0.54N0.40 and HfC0.5N0.5 for evaluations

– Demonstration of calculation of HfCN bulk modulus using Density Function

Theory (DFT), understanding the atomic bonding with dopants

Bulk Moduli For HfC, HfN and various compositions of HfCN were computed using the Vienna Ab initio Simulation Package (VASP).

C

Hf

N

22

Develop HfO2 and Hf-RE Based Coatings or Protective

Scales– Based on HfO2-HfSiOx and HfYb-SiOx systems for improved temperature

capabilities and durability

– Evaluating HfOCN stability

DFT Modeling results (by Brian Good)

Reduced SiO2

O

NC

Hf

Hf

1300°C oxidized, 75hr

23

Summary

─ Durable EBCs are critical to emerging SiC/SiC CMC component technologies

─ Multicomponent EBC oxide/silicates being developed with higher stability and

improved durability

─ HfO2-Si and RE-Si bond coats being developed for realizing 1482°C+ (2700°F+)

temperature capabilities

• Further temperature capability improvement can be improved using RE-Si+Hf

bond coats

• Multicomponent RE-Hf-silicate top coat also developed to improve combustion

steam and CMAS resistance

• Hf-Y/Yb-RE silicates system also being explored for higher temperature

capabilities

─ EBC-CMC system rig durability testing and demonstrations

─ Ultra high temperature materials also benefit from the coating and material system

technologies

2424

Acknowledgements

The work was supported by NASA Transformational Tools and Technologies

Project.

The authors are grateful to

- LME and LMC colleagues, Kang N. Lee, Craig Smith, Narottam Bansal,

Valerie Wiesner and others for helpful discussions

- Ron Phillips for assisting thermomechanical tests

- John Setlock and Don Humphrey for assisting Thermogravimetric analysis

(TGA) and oxidation tests

- Sue Puleo and Rick Rogers for X-ray analysis