Advanced Thermal Barrier Coatings for Operation in High ......Advanced Thermal Barrier Coatings for Operation in High Hydrogen Content Gas Turbines Gopal Dwivedi, Vaishak Viswanathan,Yang

DOE UTSR Meeting, Oct 2014, Purdue University, IN

Advanced Thermal Barrier Coatings for Operation in High Hydrogen Content Gas Turbines

Gopal Dwivedi, Vaishak Viswanathan,Yang Tan, Yikai Chen

Prof. Christopher M. Weyant, Prof. Sanjay Sampath

DOE UTSR Meeting, Oct 22nd, Purdue University

Dwivedi et al., JACerS, DOI: 10.1111/jace.13021

Viswanathan et al., JACerS, DOI: 10.1111/jace.13033

Dwivedi et al., JTST, Under Review

Viswanathan et al., JACerS, Under Review

DOE NETL UTSR

Contract #DE-FE0004771

2010-2014

Program Manager: Dr. Briggs while


2

Single Layer YSZ

2010

4 years 600 hrs

50 +coating conditions

40+ architectures

600+ FCT samples

Adequate erosion

resistance

Significantly higher

durability

CMAS resistance

Mechanisms and

Methodology to

incorporate andy

new composition

Snapshot of accomplishment under UTSR program

Layer-2

Layer-1

Layer-3

1,200 hrs

2014


Interplay between TBC durability and “manufactured” coating properties

o Ceramic strength/toughness o Ceramic coating compliance

and ceramic chemistry

o Bond coat chemistry, Roughness

o Ceramic coating toughness o Ceramic coating composition

o Coating density o Coating porosity/cracks

o Bond coat roughness

o Coating thickness

o Pore architecture

o Coating thickness

3


Multilayered architecture to combat multifunctional requirements

Plasma spray is naturally suited for such layered

manufacturing

Erosion, FOD, CMAS/Ash

Low-K material, Porosity,

Lower sintering rate

Remains complaint

Compatibility with Bondcoat

Mostly traditional TBC, High

toughness

Adequate roughness,

oxidation resistant (dense),

environmental effects

Mech

. A

nd

ch

em

ical

co

mp

ati

bil

ity

4


Multilayered architecture to combat multifunctional requirements

Erosion, FOD, CMAS/Ash

Low-K material, Porosity,

Lower sintering rate

Remains complaint

Compatibility with Bondcoat

Mostly traditional TBC, High

toughness

Adequate roughness,

oxidation resistant (dense),

environmental effects

5


6 Impact of water vapor on conv. & new TBC materials

No significant difference found at this temperature, and long term

exposures

HVOF bond coats (NiCoCrAlY & NiCoCrAlYHfSi) for ORNL testing

ORNL is investigating the interactions with several different substrate materials

Collaborative partnership with ORNL- Materials selection

Initia

l Results


Figure 7: This process map relates NiCr (a surrogate for NiCrAlY) particle states, achieved during liquid and gas fuel HVOF (Woka and Diamond Jet) and plasma spray (Triplex) to resultant microstructures and roughness. Significant difference among the TS bond coats exist in terms of microstructure, density and internal oxidation. These differences can dramatically affect performance. It is critical to understand these effects to optimize NiCrAlY bond coats. Maps allow for systematic tailoring of coating properties.

Not all bond coats are the same! Processing plays a role 7


Processing Effects on HVOF Bond Coats

HVOF process type and spray

conditions significantly affect

deposition stresses and final stress

state of the coaitng.

Jetkote STD JP5000 STD

Jetkote- Reducing JP5000- Reducing

JP5000 chosen due to microstructure and

compressive stress state.

8

Stress State

Evolving Thermal Residual

Str

es

s (

MP

a)

-300

-200

-100

0

100

200

Jetkote STD

Jetkote Reducing


9

Collaboration with Dr. Bruce Pint and Dr. Allen Haynes at ORNL

XPT: NiCoCrAlY

AMDRY: NiCoCrAlY-HfSi

Reactive element bondocat showed

higher life under all the conditions

Down selection of bond coat material

Pint et al., AMP May 2012


100 µm

100 µm

Fra

ctu

re in

to

pco

at

Fra

ctu

re in

TG

O

100 µm

100 µm

BC roughness effects may overshadow chemical effects? T

op c

oat

life

(h

ou

rs)

0

100

200

300

400

500

600

700

Commercial CTSR

Furnace

cycle test

24 hrs cycle

0

2

4

6

8

10

12

Ro

ug

hn

ess,

Ra (

mm

) Commercial CTSR

Bondcoat layer

require adequate

roughness for

high TBC life

10

NiCoCrAlYHfSi


Particle Diameter (m)10 100

Volu

me (

%)

0

4

8

12

16

20

AMDRY 386-2 D50

: 32.31m

AMDRY 386-4 D50

: 62.72mCoarse

Fine Particle size

Two layered architecture

Processing Control

Rough bond coat surface

Strategy

Utilize the Fine particle size for Dense Oxidation Resistant initial layer

Utilize the Coarse particle size to tailor the topography for high surface

roughness

Feedstock

Processing Strategies 11


Substrate

Layer-1: ~100µm Fine powder (Dense microstructure)

Layer-2: ~50µm Coarse powder (Rough Surface) b

on

d c

oa

t

Two layers bond coat deposition

50µm 50µm 50µm

Densest bottom layer

Poor splat cohesion

Denser bottom layer

Poor splat cohesion and some

cracking

Least dense bottom layer

Good particle melting and splat

cohesion

Deposition Scheme 12


Rene 80

NiCrAlYHfSi

YSZ

150μm

300μm

Rene 80

NiCrAlYHfSi (Two Layered)

YSZ

150μm

300μm

Rene 80

Commercial

YSZ

150μm

300μm

NiCrAlYHfSi NiCrAlYHfSi

(Two Layered)

Commercial

Similar top coats on 3 different bond coats

FOCUS : Two Layered Bond Coat

0

200

400

600

800

1000

FC

T H

ours

Improved bond coat

roughness

Performance of the Two Layered Bond Coat 13


14

Teixeira et al., JTST, 9(2), 2000—191

Padture et al., vol. 296,Science, 280,

2002

With extending service hours

TGO Growth: Additional Stress build up at

the interface. (limited control)

Sintering: loss in compliance

=> higher stress build up. Higher driving force

for crack propagation. Process optimization to

design coating with large compliance in as

sprayed condition.

Substrate

Bondcoat

TBC

σ= 0

σ = σi σ = σis

1st cool

down

nth cool

down

σis >> σi

σis ≥ σc :Failure

100µm 100µm

As-deposited TBC Failed (~600 hrs)

Failure

Mechanism

Failure mechanism of TBCs: Occurring at BC-TC interface

Majority of TBC failure occur at the BC-TC

interface. Parameter of interest is Fracture

Toughness.


15 Is the toughness sensitive to microstructure of TBCs?

Fractured X-section. APS YSZ coating

Splat

Intersplat boundaries

Pores or voids

Lamellar pores

Intrasplat cracks

1 m Some defects present more tortuous

path to a crack than others.

1µm

Splat

detachment

Fracture

through

splats

Interlamellar pore as a

possible crack path

These defects can be controlled via

processing.

Plasma spray can be utilized to produce significantly different microstructures.

Can we manipulate the effective fracture toughness of these structure?

Abradables Layered

structures Segmented

Structures

APS YSZ

50m 50m 50m

Large globular

pores

Layered structure

with thin splats

Vertical crack with

high “local” density

The defect architecture governs

Thermal conductivity and Coating

compliance


Fracture Toughness: Double Torsion Technique

PrecrackLoad, P Specimen

t

W

Wm

Notch

Max. Load for

fracture

12 mm

39- 40 mm

20

mm

16

4 point bend loading at the notched edge

Pre-cracking @ 0.001 mm/sec

Loading till fracture @ 0.01 mm/sec

21

4

13

StSPK mICIC

PIC - Maximum load at failure

- Poisson’s ratio

S - specimen width

Sm - moment arm

t - specimen thickness

- thickness correction factor

= 1-1.26(t/S)+2.4(t/S)exp(-pS/2t)

Free standing

coating

Advantages:

Does not require crack length monitoring

Can be performed a low thickness specimen (~600µm).


50µm

Coarse powder cut

50µm

Ensemble powder cut

Particle Diameter (microns) 3 30 10 100

Volu

me (

%)

0

5

10

15

20

25

30 D50: Mean particle size

D50 =96.11 µm

D50=59.75 µm

D50 =24.01 µm

En

se

mb

le

0.0

0.5

1.0

1.5

2.0

2.5

Co

ars

e

Fra

ct.

tough,

KIC

(M

Pa

-√m

)

Fin

e

50µm

Fine powder cut

Case Study: Effect of particle size distribution 17


YSZ

as-sprayed

0 10 20 30 40 50 60 70 80

Indentation modulus, Eind (GPa)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fra

ctu

re toughness, K

IC (

MP

a-√

m) YSZ

sintered

ohigh sintering

rate

ohigh intrinsic

toughness

Fracture toughness and modulus relationship

o With sintering or

densification of

microstructure,

fracture toughness

increases.

o Toughness is more

sensitive towards

sintering FC

coarse

med E

highE

lowE

fine

150mm

18

E α 1/porosity

Fracture toughness is

sensitive to coating

microstructure


19 FCT life of various APS YSZ architectures

D

50 µm 50 µm

DVC

unmolten

particles

vertical

cracks

A B

50 µm 50 µm

C

50 µm

interlamellar

pores

globular

pores microcracks

FC

T L

ife

(H

ou

rs)

0

200

400

600

800

1000

FCT Hours

FCT Hours: 784.0000

A B C D

Typical APS coatings

DVC

FC

T L

ife (

Hours

) FCT carried out at

1100oC, 24 hrs cycle

In order to limit the

compliance loss

1. Porous coatings

2. DVCs

Generally, it has been

believed that the porous

TBCs last longer.


20

0

10

20

30

40

50

60

0

1

2

3

4

Ela

stic M

odulu

s (

GP

a)

Fra

ctu

re T

ou

gh

ne

ss (

MP

a

m)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Therm

al C

onductivity (

W/m

K)

A B C D DVC*

FC

T L

ife

(H

ou

rs)

0

200

400

600

800

1000

FCT Hours

FCT Hours: 784.0000

DVC A B C D

Design requirements

Design requirements

1. High toughness : Improved Cyclic Life

2. Low modulus : Less driving force to failure

3. Low thermal conductivity : Low substrate temperature

Need a strategic approach towards

coating design for multi-functionality

Multiple requirements from a thermal barrier coating


Substrate

Bond Coat

Primary Requirement

Elastic Modulus Fracture Toughness Thermal Conductivity

Durability Thermal Performance Compliance

Function of coating

microstructure

Processing strategies can control layer by layer coating properties

Multiple requirements from a thermal barrier coating 21


Ni based Superalloy Substrate

Mu

ltila

ye

r To

pco

at

Bo

nd

co

at

Oxidation protection

strength/creep resistant

High fracture toughness layer

Sinter Resistant

Low Thermal conductivity

Erosion and CMAS Resistant

Low thermal conductivity

Phase stability

Teixeira et al., JTST, 9(2), 2000—191

Padture et al., vol. 296,Science, 280, 2002

Focus on need for high toughness ceramic at failure location 22

σis ≥ σc :Failure


23

Substrate

Bondcoat

TBC

U= 0

U = Ui

Low

stiffness

High

stiffness For constant hc

Uinterface α E (modulus)

Elastic Energy approach to optimize coating architecture

)()()1(2

)1( 2ccsubc

c

isothermal hETU -

Levi et al., MRS Bulletin, 2012

Total Elastic Energy available for

interfacial crack propagation

Failure occurs when

Uinterface ≥ Gc

UiDense > Ui

Porous EDense > EPorous

Approach: Higher toughness with denser coatings…


24

Substrate

Bondcoat

TBC

U= 0

U = Ui

Low

stiffness

High

stiffness For constant hc

Uinterface α E (modulus)

Elastic Energy approach to optimize coating architecture

)()()1(2

)1( 2ccsubc

c

isothermal hETU -

Levi et al., MRS Bulletin, 2012

Total Elastic Energy available for

interfacial crack propagation

Failure occurs when

Uinterface ≥ Gc

....)()1(2

)1(332211

2

ccccccsubc

c

isothermal hEhEhETU -

Derived from Levi et al., MRS Bulletin, 2012

For multilayer coatings


25 Revised TBC Architecture: Strategic approach for multi-functionality

Substrate

Bond Coat

Typical APS TBC

YSZ

as-sprayed

0 10 20 30 40 50 60 70 80


0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fra

ctu

re toughness, K

IC(M

Pa-√

m) YSZ

sintered

FC

coarse

med E

highE

lowE

150mm

High Plasma

Power

Fine

Particles

Sintered for 24

hours

Substrate

Bond Coat

Functionally Optimized TBC with high

fracture toughness interface layer

High

Toughness

Layer

Porous layer for

lower modulus

Crack initiation due

to TGO growth

Structural

Compliance


26

50µm 50µm 50µm

Bi-layer with tough near-

interface layer Porous single layer Bi-layer with inverse

architecture

Revised TBC Architecture

Substrate

Bondcoat

Porous architecture

Conventional TBC

Substrate

Bondcoat Layer 1 : High toughness

Layer 2 : Low modulus

Optimal bi-layered TBC Inverse bi-layered TBC

Substrate

Bondcoat


Layer 2 : High toughness


27 T

BC

lif

eti

me

(h

ou

rs)

0

200

400

600

800

1000

1200

1400

Co

nve

nti

on

al

Single layer

TBCs

Bi-layer

TBCs

Bi-layer

architecture

Inverse bi-layer

architecture

Porous Low near-

int. layer

KIC

FCT durability of revised TBC Architecture

YSZ

as-sprayed

0 10 20 30 40 50 60 70 80


0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fra

ctu

re to

ug

hn

ess, K

IC(M

Pa-√

m) YSZ

sintered

FC

coarse

med E

highE

lowE

150mm

High Plasma

Power

Fine

Particles

Sintered for 24

hours

Consistent improvement in

TBC life for bi-layer coatings

With high toughness interface

layer

Do

ub

led

li

fe


28

Bi-layer with tough near-interface layer Conventional porous single layer Bi-layer with inverse architecture

Conventional

poro

us s

ingle

layer

50 µm

C1

50 µm

B5

bi-

layer

with

dense n

ear-

inte

rfa

ce

la

ye

r

50 µm

B3

bi-

layer

with

invers

e

arc

hitectu

re

epoxy epoxy epoxy

Failed Specimens

The failure location for all the architectures remains the same

Substrate

Bondcoat

Porous architecture

Conventional TBC

Substrate

Bondcoat



Optimal bi-layered TBC Inverse bi-layered TBC

Substrate

Bondcoat




29 Process optimization strategies

Superalloy Substrate

Overlay BC

Porous

YSZ

Low K

Low E

Conventional TBCs

Enhanced

Durability TBCs

Superalloy Substrate

Overlay BC enhanced

roughness

Layer-1

Layer-2

High KIC TBC Layer

Porous

YSZ

Low K

Low E

Ne

ar-

inte

rfa

ce la

ye

r K

IC, (M

Pa

m)

bi-layer

TBCs

Inverse

bi-layer TBC

15

Effective in- plane elastic modulus, E (GPa )

20 25 30 35 40 45 50 55

2.0

2.4

2.8

3.2

3.6

1.2

1.6

B5 B6

B7 Single layer

TBCs Property based

design map for

coatings with

enhanced

durability

TB

C life

tim

e (

hou

rs)

RT Thermal conductivity (W/m-K)

0.6 0.8 1.0 1.2 1.4 1.6 1.8

400

600

800

1000

1200

1400

Single layer

TBCs

bi-layer

TBCs with

improved

durability

Inverse

bi-layer TBC

Simultaneous

optimization of

coating durability

and functionality


Traditional YSZ

New TBC Requirement

Phase Stability Good < 1200C Good


Candidates for top coat composition under consideration

Material Composition Advantages Powder

YSZ 7-8wt% YSZ Stable below 1200 C, cost effective, properties well-characterized

Various sources,

different levels

of purity

Zirconate La2Zr2O7 Pyrochlore, low thermal conductivity, phase stability to 1400 C

Julich

Zirconate Gd2Zr2O7 Pyrochlore, low thermal conductivity, phase stability to 1400 C, compatible

with YSZ

Saint Gobain,

Julich,

Co-doped 1.5mol%Yb2O3 1.5mol% Gd2O3

2.1mol% Y2O3

ZrO2

t’ phase, low thermal conductivity,

sintering resistant, compatible with

MCrAlY bond coat, high erosion

resistance

NASA

YSZ-Al-Ti YSZ+20mol%Al+5mol%Ti

CMAS resistant Ohio State Univ

TBC Materials under considerations

31


Exploring and processing new materials

Cluster-doped YSZ Gd2Zr2O7 La2Zr2O7

32


Courtesy : Levi et al MRS Bulletin 2012

Challenges:

1. CMAS mitigation

2. High erosion/FOD

resistance

3. Compatibility with YSZ

100 μm

YSZ

Gd2Zr2O7

Transitioning to low K TBC: Gd2Z2O7 pyrochlores

All have significant

dependency on processing

33


SiO2 CaO FeO Al2O3 Cr2O3 MgO SO3 TiO2 SrO MnO K2O Na2O P2O6

29.7 25.4 14.8 14.7 5.1 3.6 1.8 1.1 1.0 0.9 0.8 0.6 0.2

34

Reaction zone

~100 µm

100 µm

Porous GDZ Dense GDZ

Reaction zone

~35 µm

100 µm

Dense GDZ seems to offer lesser Lignite ash penetration depth.

It also offer benefits in terms of erosion resistance.

However, it has high modulus, which will increase the overall strain energy

Coating microstructure for enhanced CMAS resistance

Courtesy: Prof. Nitin Padture


SiO2 CaO FeO Al2O3 Cr2O3 MgO SO3 TiO2 SrO MnO K2O Na2O P2O6

29.7 25.4 14.8 14.7 5.1 3.6 1.8 1.1 1.0 0.9 0.8 0.6 0.2

35

Reaction zone

~100 µm

100 µm

Porous GDZ Dense GDZ

Reaction zone

~35 µm

100 µm

Dense GDZ seems to offer lesser Lignite ash penetration depth.

It also offer benefits in terms of erosion resistance.

However, it has high modulus, which will increase the overall strain energy

Molten ash

wicking

DVC GZO

Lignite Ash

Isothermal treatment under CMAS like conditions

Potential candidate for Top layer

Coating microstructure for enhanced CMAS resistance

Courtesy: Prof. Nitin Padture


1300C-110h

1200C-110h

1300C-10h &

1200C-110h

Various duration at 1100C and

1200C

YSZ

New

TBC Th

erm

al C

on

du

cti

vit

y (

W/m

-K)

Larson Miller Parameter (LMP)

LMP = T(ln t + C)

Larson Miller Parameter (LMP): Temp and Time for thermal exposure

36

High K, Low

Sintering rate

Sintering behavior of new materials: Challenges


Befo

re

After

Free standing bi-layer coatings

Isothermal exposure at 1200oC for 24 hours

LMP

42000 44000 46000 48000 50000 52000 54000 56000

Co

nd

ucitiv

ity (

W/m

K)

0.8

1.0

1.2

1.4

1.6

1.8

YSZ

Gd2Zr2O7

LMP (Larson Miller Parameter)

Tan et . al

Gd2Zr2O7

Big difference in sintering rates require microstructural modifications 37


GZO

as-sprayed

YSZ

as-sprayed

GZO

sintered

0 10 20 30 40 50 60 70 80


0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fra

ctu

re toughness, K

IC (

MP

a-√

m) YSZ

sintered

o high sintering rate

o high intrinsic

toughness

o low sintering

rate

o low intrinsic

toughness

Toughness is an issues with Cubic pyrochlore, GDZ

o YSZ more sensitive to

processing than GDZ

o Equivalent sintering

affects YSZ fracture

toughness more than

GDZ

FC

coarse

med E

highE

lowE

fine

150mm

med E

highE lowE

fine

38

E α 1/porosity


39

GDZ

20µm

YSZ

20µm

SE

M

Filt

ere

d

G3

20µm

Y3

20µm

Larger microcracking in GDZ due to low toughness

Introduces

processing

challenges


100 μm

YSZ

Gd2Zr2O7 A

100 μm

YSZ

Gd2Zr2O7

B

100 μm

YSZ

Gd2Zr2O7

C

0

100

200

300

400

500

600

700

TB

C L

ifetim

e (

Hours

)

Sin

gle

La

ye

r P

oro

us Y

SZ

A B

C

Porous Med. Porosity Low Porosity

FCT durability of bi-layered YSZ and Gd2Zr2O7 coatings

Failed

At YSZ-GDZ

interface

40

100μm

YSZ layer

Spalled GDZ layer

Failed microstructure (C)


Befo

re

After

Free standing bi-layer coatings

Isothermal exposure at 1200oC for 24 hours

LMP

42000 44000 46000 48000 50000 52000 54000 56000

Co

nd

ucitiv

ity (

W/m

K)

0.8

1.0

1.2

1.4

1.6

1.8

YSZ

Gd2Zr2O7

LMP (Larson Miller Parameter)

Tan et . al

Gd2Zr2O7

Big difference in sintering rates require microstructural modifications 41

Toughness of GDZ!!!


42

Y1

• YSZ and GDZ process property relationships • Process Map development

• Toughness, Lignite ash penetration depth, erosion

Y2

• Rough bond coat process optimization with 40% increase in FCT life

• Two layer dense BC layer

Y3

• bi-layer YSZ coating with two fold increase in FCT life, and maintaining low K

• High toughness interface layer, Elastic energy model

Y4 • Multilayer YSZ-GDZ coating system

• enhanced life, Lignite ash penetration minimization, erosion resistance

Systematic progress over past four years


43

CTSR

UTSR

Program

GE Aviation

Different FCT

cycling time

Praxair

Gradient Jet-test

Siemens

FCT

ORNL

Various cycling

time and

substrate

material

CTSR

Further reduction in the

cost- Bondcoat processing,

other TBC materials

CTSR

Burner rig testing with

CMAS attach

CTSR

TBC overhaul:

reclaimed substrates

Extension and evaluation of multilayer YSZ-GDZ coatings

CTSR

Deposition and testing

on an actual component


Gratefully acknowledged

Dr. Briggs While, Program Manager

Prof. Toshio Nakamura, Stony Brook University

Dr. Curtis Johnson, Rtd. GE GRC

Prof. John Hutchinson, Harvard university

Prof. Nitin Padture

Documents

Advanced Thermal Barrier Coatings for Operation in High ......Advanced Thermal Barrier Coatings for Operation in High Hydrogen Content Gas Turbines Gopal Dwivedi, Vaishak Viswanathan,Yang