Title - Arial 28pt

Slurry-Based Environmental Barrier Coatings

Kang N. Lee, Bryan J. Harder, Gustavo Costa*, and Bernadette J. Puleo

NASA Glenn Research Center, Cleveland OH

*Vantage Partners, Cleveland, OH

CIMTEC 2018, Perugia Italy

June 4-8, 2018

This work was supported by NASA Transformational Tools and Technology and Advanced Air Transport Technology programs

• https://ntrs.nasa.gov/search.jsp?R=20180005511 2020-04-14T08:10:22+00:00Z

Title - Arial 28pt

2

Implementation of ceramic matrix composite (CMC) in Gas Turbines

Combustor

linersBladetrack

(Shroud)

Blades

Vanes

• CFM International LEAPx: HPT* Shroud in A320neo (2016) & B737max (2017)

• GE 9X: Combustor Liner, HPT* Shroud, HPT* Vanes in B777x (~2019)

* High Pressure Turbine

•

L,--1 .__ ___________ .__ ________ __. '---~----,---Ar t Col'T'f)ressor 8chalst

Cold Section

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Evolution of Environmental Barrier Coatings (EBCs) at NASA

H2O(g) Si(OH)4(g) H2O(g) H2O(g)

• An external coating to protect CMCs from recession by H2O

• Enabling technology for CMCs

Gen 1 EBC (EPM: NASA-GE-PW-1997)

Gen 2 EBC(UEET: NASA-2003)

Silicon Bond Coat, mp = 1416oC(2580oF)

K. N. Lee, Surf. and Coat. Tech, 133-134 1-7 (2000).

Yb2Si2O7

SiCMC

CMC Recession

E. J. Opila et al., Am. Ceram. Soc., 80[1], 197-205 (1997)

: gas velocity

P(H2O) : water vapor pressure

PTOTAL : total pressure

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

EBC

Mullite Coating(NASA-1993)

K. N. Lee et al. ," J. Am. Ceram. Soc., 78(3) 705-710 (1995).

Next Gen EBC

(NASA Developmental)

CMC

EBC

2700oF (1482oC) Bond Coat

•

1/ 2

Volatility oc v x P(H20) 2

(PTOTAL ) 112

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• Develop next Gen EBCs with 2700oF (1482oC) bond coat capability using slurry process

• Bond coat: Yb2Si2O7-Based, Mullite-Based

• Sintering aids: Oxide-based

• Validation: Steam cycling rig, Combustion rigs

Objective

Yb2Si2O7

Steam Cycle, 1350oC, 90% H2O, 100h

TGO ~10mm

Feasibility Demonstrate of

Slurry EBC (mid 2000’s)

Cleveland State Univ./NASA (J. Euro. Ceram. Soc., 1123-1130, 2011)

Planetary Mill (Submicron coating

powders)

Organic processing aids

(Coating powders+ Processin aids +Solvent

Processing (Dip, Spin-Dip, Spraying)

Drying (Burnout organic

Sintering (Consolidate coating)

Particle size analysis

Zeta otential

Dilatometer

Test & Characterization

•

Lift

Cycle

Temp Up to "'2700F

Velocity "'10 cm/s

Water vapor Up to "'0.9 atm

Pressure latm

Title - Arial 28pt

5

5,366-h GE Shroud Rig Test 15,144-h Solar Combustor Liner Engine Test

GE Final Report – DOE AMAIGT Program, Dec. 2010J. Kimmel et al., ASME paper GT2003-38920, ASME TURBO EXPO, Atlanta, GA, USA, June 16-19, 2003.

Key EBC Failure Mode: Oxidation-Induced Spallation

• Water vapor (H2O) is the primary oxidant

• SiO2 TGO (thermally grown oxide) forms due to Si bond coat oxidation

• Growth stress (~2.2x volume expansion)

• Phase transformation stress (~5% volume expansion due to b to a cristobalite at ~200oC)

• CTE* mismatch stress (a cristobalite =10.3 x 10-6/C vs. Yb2Si2O7 = 4.7, Si = 4.4, SiC = ~5)

• Causes large residual stresses that provide the strain energy release rates required to drive EBC delamination cracks

*Coefficient of thermal expansion

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100h/100 cycles

500h

As-Sintered

CMC CMC

100h

TGO

TGO

Bond Coat

Top Coat

80 mm

80 mm

20 mm

As-Sintered

Bond Coat

Top Coat

Bond Coat

Top Coat

• Yb2Si2O7-based top coat for recession resistance• Sintered at T>2700oF (1482oC)• Excellent microstructural & chemical stability • EBC remained adherent after 500h

Slurry EBC w/ Yb2Si2O7-Based Bond Coat

[Steam Oxidation: 1 hr at 2600oF (1427oC) / 20 min at T<100oC, 90% H2O]

TGO

--------- - •

Title - Arial 28pt

7

100h

CMC

Chem Barrier

Top Coat

Bond Coat

As-Sintered Bond Coat

CMC

80 mm

20 mm

500h

80 mm

TGO

CMCTGO

Chem Barrier

Top Coat

Bond Coat

• Yb2Si2O7-based top coat for recession resistance•HfSiO4-based chemical barrier

• Yb2Si2O7-Mullite Eutectic = ~1500oC

• Sintered at T> 2700oF (1482oC)• Excellent microstructural & chemical stability• EBC remained adherent after 500h

Slurry EBC w/ Mullite-Based Bond Coat

[Steam Oxidation: 1 hr at 2600oF (1427oC) / 20 min at T<100oC, 90% H2O]

TGOTGO

~ J .., . :; ~ ... ",.) ..... • ..,,.., • • -., ;- • I (iJ •, ~ ~;,• •·._ .,, ...... ~ ' .,

•

Title - Arial 28pt

8

Time, Hrs

CMC

Yb2Si2O7-Based EBCMullite-Based EBCInternal Surface

Si (10% O2)*

* Extrapolated from Deal and Grove, J. Appl. Phys., 36[12] 3770-78 (1965)

Steam Oxidation Rates of Slurry EBCs in Steam Cycling[2700oF (1482oC) in 90% H2O+10% O2, 1h cycles]

• Both slurry coatings provide substantial mitigation of steam oxidation• Mullite-based bond coat shows slightly lower TGO growth rates

• TGO is thicker on the internal surface (~25%) than under the EBC• Oxidation mechanism studies in progress

35

30

Ill C 25 e

.!::! ~ 20 .. Ill Ill a, C

,.:=.:: 15 .!::! .c l-o 10

~ 5

0 • ~

, , , ,

, , , ,

, , , , ,

, , , , , --

I

------__ ... -------* --o+ 10% O_i~----------. 10.0°lo \-\1. ------

S\ ''? ------------------

0 ~ •

-----------------------------0 n-........ -,.,,-:..::-:..::-___________________________ _ 0 100 200 300 400 500

•

Title - Arial 28pt

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Parabolic Oxidation Plot of Slurry EBCs[1 hr at 2600oF (1427oC) / 20 min at T<100oC, 90% H2O]

Substrate CVI* CMC CVI* CMC CVI* CMC

Coating Yb2Si2O7-Based Mullite-Based Uncoated(Internal Surface)

k (mm2/h) 0.70 0.47 2.11

• Parabolic rate constant is ~50% higher with Yb2Si2O7-Based bond coat• Uncoated CMC (Internal surface) shows ~2x – 3.5x higher parabolic rate

constant than coated CMC

YbDS-Based EBC

Mullite-Based EBC

*Chemical vapor infiltration

450 r-J

E 400 :::i.

350 r-J - 300 Vl

C

~ 250 u

£ 200

I- 150 0

~ 100

- so 0

.. . ... .... \~~-_. ............... a·· 0 100

k =0.7043 O

.... •·~

ij ....................... •····: .... -o -··Q ······· ········

W•·········· ··•' .... k = 0.4705 .... •· ········· ····· ····· ......

200 300

Time, Hrs

400 500

•

Title - Arial 28pt

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Spin-Dip CoaterSlurry EBC-coated

3”x3” CMC Airfoil

• Durability testing in a combustion rig at 2500oF-2700oF (1371-1482C) is in progress• Steam cycling test of witness coupons at 2600oF (1427C) in progress

•

Title - Arial 28pt

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EBC on Monolithic SiC (3”x 3”) – 1st Airfoil Spin-Dip Trial

As-Coated

100h-100 cycles at 2700oF in Air

Leading

Edge

Trailing

Edge

20 mm

• Demonstrated 2700oF (1482C) temperature capability in air cycling• SiC substrate broke due to thermal shock

•

Title - Arial 28pt

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Slurry EBC Fabrication on Mini-composite (via Air Brush)

As-Deposited and Dried(Fractured Surface)

As-Sintered(Polished Surface)

Top Coat

Bond Coat

Top Coat

Bond Coat

• Steam oxidation and mechanical testing in progress

100 mm

200 mm

30 mm

30 mm

•

Title - Arial 28pt

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Time, hr

Uncoated, Air

Coated, Steam

Coated, Air

Cyclic Oxidation of Slurry EBC on SiC Heating Element(1 hr at 2600oF (1427oC) / 20 min at T<100oC, 90% H2O)

• High oxidation rate of uncoated SiC due to additives and high porosity • EBC is effective in reducing oxidation rate in air and steam

SiC

EBC

EBC

We

igh

t g

ain

. m

g/c

m2

100 mm

30 mm

SiC

5

4

3

2

1

0 0 20 40

•

60 80 100

Title - Arial 28pt

Conclusion

Two slurry-based EBCs capable of 2700oF have been developed

Low-cost, non-line-of-sight EBC technology

Coating can be readily applied on components of various complexities

and shapes

Coated coupons demonstrated 500h-500 cycle steam oxidation

durability at 2600oF (1427C)

Parabolic oxidation rate is ~1/3 of the rate on uncoated internal CMC surface

Coated SiC airfoil demonstrated 100h-100 cycle cyclic durability in

air at 2700oF (1482C)

A spin-dip coating process developed for airfoils

Coated CMC airfoil combustion rig test at 2500oF-2700oF (1371-

1482C) in progress

14

•

Title - Arial 28pt

Deborah Waters for the initial development work of slurry

EBCs (NASA GRC)

John Setlock for air brush spraying of slurry EBC on mini-

composites (University of Toledo)

Dagny Sacksteder for testing of EBC-coated SiC heating

elements (Summer Intern, The Ohio State University)

15

Acknowledgement •