novel functional graded thermal barrier coatings in coal-fired

Novel Functional Graded Thermal Barrier Coatings in Coal-fired Power Plant Turbines

Jing Zhang Department of Mechanical Engineering

Indiana University-Purdue University Indianapolis

Grant No.: DOE DE-FE0008868Program Manager: Richard Dunst

2016 CROSSCUTTING RESEARCH AND RARE EARTH ELEMENTS PORTFOLIOS REVIEWPittsburgh, PA, April 18–22, 2016

2

Acknowledgement

• Subcontract: James Knapp (Praxair Surface Technologies)• Collaborators: Li Li, Don Lemen (Praxair Surface

Technologies)• Yeon-Gil Jung (Changwon National University), Ungyu Paik

(Hanyang University)• Yang Ren, Jiangang Sun (Argonne National Laboratory)• Changdong Wei (OSU), Bin Hu (Dartmouth)• Ph.D. graduate students: Xingye Guo, Yi Zhang

3

Outline• Introduction• Coating design and fabrication

• Single ceramic layer (SCL) &Double ceramic layer (DCL) architectures• Composite coatings with buffer layers

• Characterization of physical and mechanical properties• Microstructure and composition• Porosity and hardness• Bond strength test• Erosion test

• Characterization of thermal property and thermal durability• Thermal conductivity, specific heat, coeff. of thermal expansion• Thermal shock (TS) test• Jet engine thermal shock (JETS) test• Furnace cycling thermal fatigue (FCTF) test• Thermal gradient mechanical fatigue (TGMF) test

• MD&FE modeling of thermal conductivity; DFT calculation of gas adsorption• Summary and future work

4

Limitation of yttria stabilized zirconia

Zirconia partially stabilized with 7~8 wt% yttria (YSZ) is the current state-of-the-art thermal barrier coating material.

The thermal conductivity of 8YSZ is ~2.12 W/m-K @ 800oC. Lower thermal conductivity materials are required for future gas turbines.

Above 1200 oC, YSZ transforms from t’ phase to the tetragonal and cubic phase (t and c phases, respectively) during cooling process, and then to monoclinic (m) phase with a volume expansion of about 3–5 vol.%, resulting in the spallation or delamination of TBCs.

Additionally, at temperatures above1200 oC, YSZ layers are prone to sintering, which increases thermal conductivity and makes them less effective. The sintered and densified coatings can also reduce thermal stress and strain tolerance, which can reduce the coating’s durability significantly.

5

Motivation and objective

• To further increase the operating temperatures of turbine engines, alternative TBC materials with lower thermal conductivity, higher thermal stability and better sintering resistance are required.

• The objective of the project is to develop a novel lanthanum zirconate (La2Zr2O7) based multi-layer thermal barrier coating system.

• The ultimate goal is to develop a manufacturing process to produce pyrochlore oxide based coatings with improved high-temperature properties.

6

Pyrochlore - A2B2O7

Pyrochlore-type rare earth zirconium oxides (Re2Zr2O7,Re = rare earth) are promising candidates for thermal barrier coatings, high-permittivity dielectrics, potential solid electrolytes in high-temperature fuel cells, and immobilization hosts of actinides in nuclear waste.

Pyrochlore crystal structure: A2B2O7. A and B are metals incorporated into the structure in various combinations. (credit: NETL)

7

Why La2Zr2O7?

• Lower thermal conductivity• Higher temperature phase

stability. No phase transformation

• Lower sintering rate at elevated temperatures

• Lower CTE

Phase diagram of La2O3–ZrO2

Compared with YSZ, La2Zr2O7 has

8

La2Zr2O7 vs. YSZ

Materials property 8YSZ La2Zr2O7

Melting Point (oC) 2680 2300Maximum Operating Temperature (oC) 1200 >1300Thermal Conductivity (W/m-K) (@ 800oC )

2.12 1.6

Coefficient of Thermal Expansion (x10-6/oC) (@1000 oC)

11.0 8.9-9.1

Density (g/cm3) 6.07 6.00Specific heat (J/g-oC) (@1000 oC) 0.64 0.54

9

Layered coating architecture

• The coefficient of thermal expansion of La2Zr2O7(~9x10-6 /oC) is lower than those of both substrate and bondcoat (~15x10-6/oC @ 1000 oC). As a result, the thermal cycling properties may be a concern

• The layered topcoat architecture is believed to be a feasible solution to improve thermal strain tolerance

• In this work, we develop multi-layer, compositionally graded, pyrochlore oxide based TBC systems

10

La2Zr2O7 spray powder morphology Powder surface morphology

•Spherical shape with a rough surface•Good flowability and high density•Particle size between 30 ~ 100 μm

+ 125 um - 125 um

Powder cross-section

•Porous interior

11

TEM image of La2Zr2O7

500 nm

credit: Bin Hu @ Dartmouth

12

La2Zr2O7 powder XRD analysisPhilips, NL/X''Pert PRO MPD, Eindhoven, NetherlandsKα1 wavelength: 1.5405600 Ǻ

XRD data show that the powder composition is La2Zr2O7

20 30 40 50 60 70 80

Cou

nts

(a.u

.)

2 Theta (deg.)

(2 2 2)

(4 0 0)

(3 3 1)(5 1 1)

(4 4 0) (6 2 2)

(4 4 4)(8 0 0)

(6 6 2)(8 4 0)

13

Synchrotron XRD

in situ synchrotron XRD shows no compositional change from 30 – 1400 oC.

Wavelength 0.108 Å

2θ (o)

Cou

nt (a

.u.)

credit: Yang Ren @ ANL

14

Coating fabrication using APS• La2Zr2O7 coatings were deposited using air plasma spray (APS)

technique by a Praxair patented plasma spray torch.• Haynes 188 superalloy was used as the substrate.

• The bond coat is Ni-based intermetallic LN-65 using APS, with a thickness of 228 μm

• Controlled spray parameters: • Powder feed ratio• Torch current• Torch gas (Argon), Carrier gas (Argon), Shield gas (Argon),

Secondary gas (Hydrogen)• Standoff distance• Sample rig surface rotation speed (RPM and surface speed)

LN-65 Ni Cr Al Y O(w%) 67.3 21.12 9.94 1.02 0.19

Haynes 188 Co Ni Cr W Si C La Fe Mn(w%) 39 22 22 14 0.35 0.10 0.03 3 1.25

15


• Single ceramic layer (SCL) – Dense Coat• Composite coatings with buffer layers




16

Cross sectional view of dense coating 1 2 3

4 5 6

Processing parameters (powder feeding rate, surface speed, current, stand off ) were varied to control the porosity.

17

200 400 600 800 1000 1200 1400 1600 1800 2000 22000

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

■ : 5279-13 line #1 ● : 5279-14 line #2▲ : 5279-15 line #3▼ : 5279-17 line #5◀ : 5279-18 line #6

Youn

g’s

mod

ulus

(GP

a)

Displacement (nm)

Nanoindentation Young’s modulus vs. displacement

18

0

20

40

60

80

100

120

140

160

180

200

159.50 ± 5.73156.00 ± 10.03

133.02 ± 9.52

121.76 ± 6.81116.26 ± 5.85

5279-13 line #1 5279-14 line #2 5279-15 line #3 5279-17 line #5 5279-18 line #6

Youn

g’s

mod

ulus

(GP

a)Nanoindentation Young’s modulus

Specimen species

19

0

1

2

3

4

5

6

7

8

9

10

11

12

Har

dnes

s (G

Pa)


10.2 ± 0.5 8.8 ± 2.1

7.87 ± 0.7

7.3 ± 0.67.0 ± 0.6

Nanoindentation hardness

Specimen species

5279-15 line #310μm 10μm

20

0

1

2

3

4

5

6

H

ardn

ess

(GP

a)


5.41 ± 0.33 5.51 ± 0.255.32 ± 0.28

4.85 ± 0.29 4.82 ± 0.24

Specimen species

Vicker’s indentation hardness

5279-15 line #310μm 10μm

21

Rockwell’s indentation hardness

0102030405060708090

5279-13-#1 5279-14-#2 5279-15-#3 5279-16-#4 5279-17-#5 5279-18-#6

Rockwell hardnessPorosity (%)

• Low density coatings with porosity between 7~10 % were achieved. • Porosity and hardness can be tuned via changing processing conditions• Powder feed rate↑ or current↓ porosity↑ hardness↓

[Hardness = 1.99×(100-porosity) -100]

22


• Single ceramic layer (SCL) – Porous Coat• Composite coatings with buffer layers




23

Cross sections of SCL La2Zr2O7 coatings

#1 #2 #3 #4 #5

24

Vickers hardness indentation

#1 #2 #3 #4 #5

10 µm 10 µm 10 µm

10 µm

10 µm

10 µm 10 µm 10 µm 10 µm 10 µm

10 µm

10 µm

10 µm10 µm10 µm

25

Nanoindentation

5 µm

5 µm 5 µm

5 µm

5 µm5 µm

#3 #4 #5

5 µm

5 µm

5 µm

26

0

1

2

3

4

5

6

H

ardn

ess

(GP

a)

4.22 ± 0.14 4.22 ± 0.20 3.97 ± 0.44 4.09 ± 0.30 3.90 ± 0.45

Samples#1 #2 #3 #4 #5

Vickers indentation hardness

27

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

Yo

ung’

s m

odul

us(G

Pa)

Displacement (nm)

■ : #1■ : #2■ : #3■ : #4■ : #5

Nano indentation Young’s modulus vs. displacement

28

0

20

40

60

80

100

120

140

Youn

g’s

mod

ulus

(Gpa

)

#1 #2 #3 #4 #5

89.04 ± 8.83

104.28 ± 9.45

100.83 ± 4.08101.11 ± 10.72

91.77 ± 14.55

Samples

Nanoindentation Young’s modulus

29

0

1

2

3

4

5

6

7

8

9

H

ardn

ess

(GP

a)

5.24 ± 1.14

6.09 ± 1.06

5.41 ± 0.13

5.41 ± 0.82 4.88 ± 1.44

Samples#1 #2 #3 #4 #5

Nanoindentation hardness

30

Porosity of low density SCL coating

Line # Density (g/cm3) Porosity (%)

7 5.3182 11.36

8 5.2587 12.36

9 5.2584 12.36

10 5.2917 11.81

11 5.2614 12.31

12 5.0089 16.52

Low density coatings with porosity between 11~17% were achieved.

31


• Double ceramic layer (DCL) coats• Composite coatings with buffer layers




32

Double ceramic layer (DCL) architectures

Bond coat (NiCrAlY)

Porous La2Zr2O7 top

coat

Substrate (Haynes-188)

432μm

228 μm 12

7 μm

Bond coat (NiCrAlY)

Porous La2Zr2O7 coat

Substrate Haynes-188

Porous 8YSZ coat

305 μm

228 μm

#6

Bond coat (NiCrAlY)

Porous 8YSZ top coat

Substrate (Haynes-188)

432μm

228

μm

#7 #8

127 μm

Bond coat (NiCrAlY)

Porous La2Zr2O7 coat

Substrate Haynes-188

Dense 8YSZ coat

305 μm

228 μm

#9

33

Interfaces of DCL coatings

#6 La2Zr2O7 and bond coat interface

#8 La2Zr2O7 and porous 8YSZ interface #9 La2Zr2O7 and dense 8YSZ interface

#7 porous 8YSZ and bond coat interface

34

Energy-dispersive X-ray spectroscopy

34

Applied heat treatments on sample #8: 8 La2Zr2O7 and porous 8YSZ

Heat treatment1080℃ 4h

Ar atmosphere

LD La2Zr2O7, 12 mils

LD 8YSZ, 5 mils

35

Vickers hardness of DCL coatings

0

1

2

3

4

5

6

7

8

9

Sample 9Sample 8Sample 6

La2Zr2O7 layer

Dense 8YSZ layerPorous 8YSZ layer

Har

dnes

s (G

Pa)

Sample 7

3.58±1.013.96±0.6

4.86±1.66

3.21±0.77

7.05±1.01

4.32±0.6

36






37

Bond strength testEpoxy (FM 1000 adhesive film) to glue coating buttons to a mating cap. Tensile test according to ASTM-C-633.

8YSZLa2Zr2O70

2

4

6

8

10

12

14

16

0

2

4

6

8

10

12

14

16

Sample 7 Porous 8YSZ

Strength

10.48±1.66 MPa

13.59±1.97 MPa

5.31±0.33 kN

Stre

ngth

(MP

a)

Lo

ad (k

N)

Load

6.88±0.99 kN

Sample 6, SCL La2Zr2O7

38

Residual stress distribution in coating

-3.2 -2.8 -2.4 -2.0 -1.6 -1.2 -0.8 -0.4 0.0 0.4-200

-150

-100

-50

0

50

100

150

Res

idua

l stre

ss (G

Pa)

Distance (mm)

Townsend et al

Zhang et al

Bond coat

Substrate

La2Zr2O7

1

( )n

k ki k i

k s s

E tT TE t

ε α α α=

= Δ Δ + − Δ

1

ni i

si s s

E t TE t

ε α=

= − Δ Δ

( )11

22

ns i i

i ii s s

t E t h tE t

δ −=

= − +

21

6ni i

i s s

E t TKE t

α=

Δ Δ= −

where α is the coefficient of thermal expansion (CTE), k is the ceramic coating layers range from 1 to n, ti is the thickness of ith layer.

( )s s sE K zσ ε δ= + + ( )i i iE K zσ ε δ= + +

X.C. Zhang, Thin Solid Films, 488 (2005) 274-282.

where

Guo et al., Thermal properties, thermal shock and thermal cycling behavior of lanthanum zirconate based thermal barrier coatings, Metallurgical and Materials Transactions E, (DOI: 10.1007/s40553-016-0070-4)

39

Erosion test

#9, La2Zr2O7 +Dense 8YSZ#7, Porous 8YSZ. #8, La2Zr2O7 +Porous 8YSZ#6, Single layer La2Zr2O7

• 600±0.2g alumina sands with a diameter of 50 μm

• Spray rate 6 g/s; duration 100 s; spray angle 20o

40

0

200

400

600

800

1000

Sample 9Sample 8Sample 7Sample 6

Crit

ical

vel

ocity

(m/s

)

La2Zr2O7

Porous 8YSZ

Dense 8YSZ

Erosion rate & critical erosion velocity

3/4 3

13/4 1/2 3/2105 ICcrit

E KVH Rρ

=

Critical erosion velocity is used toexpress the critical condition to initiatecracks [2]:

0

400

800

1200

1600

2000

2400

1562.0±25.8

1858.8±12.8

Sample 9Sample 8Sample 7

Ero

sion

rate

(μg/

g)

Sample 6

831.3±20.7

1914.6±7.3

Erosion rate describes the erosionresistance of TBC sample [1]:

[1] D. Park, Int J Adv Manuf Technol, 23 (2004) 444-450. [2] R.G. Wellman, Wear, 256 (2004) 889-899.

E: Young’s modulusH: hardnessKIC :fracture toughnessρ: density of erodent particleR: particle radius

41

Relationship between Vcrit and erosion rate

800 1000 1200 1400 1600 1800 20000.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

1/

Crit

ical

vel

ocity

(s/m

)

Erosion rate (μg/g)

● Sample 1 ▲ Sample 2■ Sample 3◆ Sample 4

6789

42






43

Thermal conductivityThermal conductivity is determined from thermal diffusivity Dth, specific heat capacity Cp, and measured density ρ:

Thermal diffusivity is measured using laser flash diffusivity system (TA instrument DLF1200). Specific heat is measured by analytical method (TA instrument DLF1200)

k = Dth·Cp·ρ

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 200 400 600 800 1000

Spe

cific

hea

t (kJ

/kg/

o C)

Temperature (oC)

-

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800 1000

Ther

mal

con

duct

ivity

(W/m

/o C)

Temperature (oC)

Sample #6 porous La2Zr2O7

Porous 8 wt% YSZ sample

Guo, et al., Thermal properties, thermal shock and thermal cycling behavior of lanthanum zirconate based thermal barrier coatings, Metallurgical and Materials Transactions E, (DOI: 10.1007/s40553-016-0070-4)

44

3

4

5

6

7

8

9

10

11

12

0 200 400 600 800 1000 1200 1400

Coe

ffici

ent o

f the

rmal

exp

ansi

on (×

10-6

/K)

Temperature (oC)

This work

LZ CTE expriment ( Lehmann )

8YSZ CTE expriment ( Hayashi )

LZ CTE Experiment ( Zhang )

LZ CTE Experiment ( Kutty )

LZ CTE Experiment ( Xu )

H. Lehmann, D. Pitzer, G. Pracht, R. Vassen, D. Stöver, Journal of the American Ceramic Society, 86 (2003) 1338-1344.H. Hayashi, T. Saitou, N. Maruyama, H. Inaba, K. Kawamura, M. Mori, Solid State Ionics, 176 (2005) 613-619.J. Zhang, J. Yu, X. Cheng, S. Hou, Journal of Alloys and Compounds, 525 (2012) 78-81.K.V.G. Kutty, S. Rajagopalan, C.K. Mathews, U.V. Varadaraju, Materials Research Bulletin, 29 (1994) 759-766C. Xu, C. Wang, C. Chan, K. Ho, Physical Review B, 43 (1991) 5024-5027.

CTE is measured using a BAEHR dilatometer from 25 to 1400 oC.

Coefficient of thermal expansion (CTE)


45





• MD&FE modeling of thermal conductivity;DFT calculation of gas adsorption• Summary and future work

46

La2Zr2O7 thermal conductivity calculation1x1x20 super cell

Replicate 20 conventional cells along the heat flow direction to form a super cell

(K)

The calculated thermal conductivity is 1.2 W/m/K at the temperature of 1000 oC, which is reasonably in agreement with the experimentally measured thermal conductivity ~1.5 W/m/K [1].

[1] R. Vassen, X. Cao, F. Tietz, J. Am. Ceram. Soc., 83 (2000) 2023–2028.Guo, et al., Image-Based Multi-Scale Simulation and Experimental Validation of Thermal Conductivity of Lanthanum Zirconate, International Journal of Heat and Mass Transfer, (doi:10.1016/j.ijheatmasstransfer.2016.04.067)

47

Imaged based FEM calculation of thermal conductivity of La2Zr2O7 TBC

k=0.723 W/m/K

k=0.538 W/m/K

k=0.550 W/m/K

Thermal conductivity of fully dense LZ k=1.5 W/m/K

SEM image Binary image FEM model

Guo, et al., Image-Based Multi-Scale Simulation and Experimental Validation of Thermal Conductivity of Lanthanum Zirconate, International Journal of Heat and Mass Transfer, (doi:10.1016/j.ijheatmasstransfer.2016.04.067)

48

Imaged based FEM calculation of thermal conductivity of La2Zr2O7 coating

Calculated thermal conductivity ~0.60 W/m-K, in good agreement with experimental data.

Guo, et al., Image-Based Multi-Scale Simulation and Experimental Validation of Thermal Conductivity of Lanthanum Zirconate, International Journal of Heat and Mass Transfer, (doi:10.1016/j.ijheatmasstransfer.2016.04.067)

49

TBC: Material: La2Zr2O7Thickness: ~600μm (this is used in calculation)Density: 90.55% dense, dense density=6 g/cc, so density ρ = 5.478 g/ccSpecific heat: c = 0.54 J/g-K @1000C

Substrate (following are room temperature properties obtained from matweb):Material: Haynes 188Density: ρ = 8.98 g/ccThermal conductivity: k = 10.4 W/m-K,Specific heat: c = 0.403 J/g-K, (therefore, ρc = 3.62 J/cm3-K)Thickness used in calculation: L = 4 mm (may have a small effect to results)

Sample information

Test conditionFlash thermal imaging test with one flash lampImaging speed: 994 Hz; imaging duration: 3 seconds

Mapping thermal conductivity & heat capacity

50

Thermal conductivity and heat capacity map

TBC is 90.55% dense (ρ=5.478g/cc), with a nominal thickness of 600μmIndentation marks are from previous study

credit: Jiangan Sun @ ANL

51

Mapping TBC thermal properties

Predicted average TBC properties (within red rectangular area): k = 0.55 W/m-K, ρc = 2.16 J/cm3-K

Thermal conductivity k image Heat capacity ρc image

0 1 W/m-K 0 2.5 J/cm3-K

These results were based on a TBC thickness of 600 μm TBC specific heat @RT: c = 0.393 J/g-K; predicted TBC density is: ρ=ρc/c=2.16/0.393=5.5 g/cc

credit: Jiangan Sun @ ANL

52





• MD&FE modeling of thermal conductivity, DFT calculation of gas adsorption• Summary and future work

53

CO2 adsorption on coating surfaces

Guo, et al., Carbon dioxide adsorption on lanthanum zirconate nanostructured coating surface: a DFT study, Adsorption, 22(2), pp 159-163, (2016)

Top view of CO2 adsorption sites on La2Zr2O7 planes. Only La2Zr2O7 top layer is shown

(a) (001) plane (b) (011) plane (c) (111) plane

(111) plane(011) plane(001) plane

-4

-3

-2

-1

Adso

rptio

n en

ergy

(eV)

0

-0.5618-0.8573

-4.1556

CO2 is prone to be adsorbed on (111) plane, when the adsorption occurs in the bridge sites between La atom and Zr atom.

54

O2 adsorption on coating surfaces

(a) (b) (c)La2Zr2O7

plane

A: bridge position

(La-Zr) (eV)

B: 4-fold

position (eV)

C: 3-fold-FCC

position (eV)

D: 3-fold-HCP

position (eV)

(001) -3.5127 -5.1148 - -

(011) -5.0240 -1.3080 - -

(111) -3.5795 - -5.5302 -3.8070

Computational slab models of various La2Zr2O7 planes: (a) (001) plane, (b) (011) plane, and (c) (111) plane. The blue, green, and red balls indicate La atoms, Zr atoms, and O atoms, respectively.

The adsorption energies are exothermic. The lowest adsorption energy site is the 3-fold-FCC on (111) plane, confirmed by Bader charge transfer analyses.

Guo, et al., First Principles Study of Nanoscale Mechanism of Oxygen Adsorption on Lanthanum Zirconate Surfaces, Physica E, (doi:10.1016/j.physe.2016.04.012)

55




• Characterization of thermal durability• Thermal conductivity, specific heat, coeff. of thermal expansion• Thermal shock (TS) test• Jet engine thermal shock (JETS) test• Furnace cycling thermal fatigue (FCTF) test• Thermal gradient mechanical fatigue (TGMF) test


56

Jet engine thermal shock tests (JETS)• Jet engine thermal shock (JETS) tests are

conducted to investigate the thermal cycling performance.

• TBC samples are heated to 2250 oF (1232.2 oC) at the center for 20 s, and then cooled by compressed N2 cooling for 20 s, and then ambient cooling for 40 s.

• Temperatures are measured by thermal couple and pyrometer.

57

Jet engine thermal shock test (JETS) results

Single layer La2Zr2O7 Porous 8YSZ+ La2Zr2O7 Dense 8YSZ+ La2Zr2O7 Porous 8YSZ

Single-layer

La2Zr2O7

Porous 8YSZ +

La2Zr2O7

Dense 8YSZ +

La2Zr2O7

Single-layer

porous 8YSZ

Number of cycles 25 > 2000 885 > 2000

Failure statusComplete

delaminated

Edge

delaminated

Complete

delaminatedIntact


58

Thermal gradient mechanical fatigue (TGMF)

0 10 20 30 400

200

400

600

800

1000

Time (minute)

Tem

pera

ture

(�)

0

50

100

150

200

Ten

sile

load

(MP

a)

Sample

Sample jig

TorchThermalcouple

Load sensor

Sample Test cycleSCL porous 8YSZ 1200

DCL porous 8YSZ + La2Zr2O7 220

DCL dense 8YSZ + La2Zr2O7 50

At 850 oC

Sample Test cycleDCL porous 8YSZ + La2Zr2O7 38

DCL dense 8YSZ + La2Zr2O7 49

At 1100 oC

59






60

Composite coatings with buffer layers

Bond coat (NiCrAlY)

La2Zr2O7 (50 vol%) +

8YSZ (50 vol%)coat

Substrate

430μm

A

60 μ

m

Bond coat (NiCrAlY)


8YSZ (50 vol%)coat

Substrate

Porous YSZ coat

370μm

B

120 μm

Bond coat (NiCrAlY[1])


8YSZ (25 vol%)coat

Substrate

310μm

D

LZ (25)+YSZ (75)

Porous YSZ coat

60 μm

In order to improve the thermal durability in thermal cycling tests, new composite top coats are proposed:thermal conductivity + matching CTEs

Introducing 1st buffer layer:Increasing strain compliance + Decreasing CTEs mismatch

2nd buffer layer:Further decrease CTEsmismatch

Bond coat (NiCrAlY)


8YSZ (75 vol%)coat

Substrate

430μm

C

Song, et al., Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings, ICMCTF 2016

61

As-coated composite coatings: microstructure, composition, hardness and Young’s modulus

100 μm

0 50 100 150 200 250 300

0

20

40

60

80

100

120

140

LanthanumZirconium

0 50 100 150 200 250 300

0

50

100

150

200

250

300

100 μm

LanthanumZirconium

100 μm

0 50 100 150 200 250 300

0

20

40

60

80

100

120

140

LanthanumZirconium

0 50 100 150 200 250 300

0

20

40

60

80

100

120

140

LanthanumZirconium

100 μm

Distance from surface (μm) Distance from surface (μm) Distance from surface (μm) Distance from surface (μm)

A-1 B-1 C-1 D-1

0

20

40

60

80

100

0

2

4

6

8

10

Hardness (G

Pa)

Ela

stic

mod

ulus

(GPa

)

InterfaceTop coat Bond coat0

20

40

60

80

100

120

140

160

0

2

4

6

8

10

Hardness (G

Pa)

Ela

stic

mod

ulus

(GPa

)


20

40

60

80

100

0

2

4

6

8

10

Hardness (G

Pa)

Ela

stic

mod

ulus

(GPa

)


20

40

60

80

100

120

0

2

4

6

8

10

Hardness (G

Pa)

Ela

stic

mod

ulus

(GPa

)

InterfaceTop coat Bond coat

A-2 B-2 C-2 D-2

A-3 B-3 C-3 D-3

CPS

CPS

CPS

CPS

Position Position Position Position

62

Thermal durability tests

• Top surface temperature : ~ 1100 ℃• Bottom surface temperature : ~ 950 ℃• Heating time : 40 min• Cooling type : Air & gas cooling

Thermocouple

Thermocouple

Aircooling

40 min40 min

Furnace cycling thermal fatigue (FCTF)

• Flame temperature : ~1400 ℃• Holding time : 20 sec • Cooling time : 20 sec• Cooling type : Nitrogen quenching

(1400 °C)

(260 °C)

Jet engine thermal shock (JETS)

• Heating temperature : ~ 1100 oC• Heating time : 40 min• Cooling type : Water quenching (30 oC)

Water cooling

Water cooling

40 min40 min

Thermal shock (TS)

Aircooling

Thermal gradient mechanical fatigue (TGMF)

63

Thermal durability of composite coatingsSample species FCTF test/Status TS test/Status JETS test/Status

(A) SLC TBC (50% LZ : 50 % YSZ

in volume)

540 cycles/Fully delaminated



(B) DLC TBC (50% LZ : 50 % YSZ

in volume) with single buffer layer



2000 cycles/Sound condition

(C) SLC TBC (25% LZ : 75 % YSZ

in volume)



1022 cycle/Fully delaminated

(D) DLC TBC (50% LZ : 50 % YSZ

in volume) with double buffer layers


54 cycles/Partially delaminated


64

Cross-sectional view after furnace cycling thermal fatigue (FCTF) test

100 μm

A-1

100 μm

B-1

100 μm

D-1

100 μm

C-1

A-2

50 μm

B-2

50 μm

D-2

50 μm

C-2

50 μm


• Delamination within top coat and/or the interface between the top and bond coats in A, B, and C.

• Thermally grown oxide (TGO) layer at interface between the top and bond coats in all samples

• Spinel (Cr2O3, NiAl2O4) in the TGO in D due to longer thermal exposure.

65

Cross-sectional view after thermal shock (TS) test

100 μm

A-1

100 μm

B-1

100 μm

D-1

100 μm

C-1

A-2

50 μm

B-2

50 μm

D-2

50 μm

C-2

50 μm

• In TS tests, A and C were delaminated less than 15 cycles, showing a thinner TGO layer than those in FCTF tests, due to CTE difference and low fracture toughness of LZ.

• B (survived 29 cycles, fully delaminated) and D (54 cycles, partially delaminated).

66

Cross-sectional view after jet engine thermal shock (JETS) test

100 μm

A-1

100 μm

B-1

100 μm

D-1

100 μm

C-1

A-2

50 μm

B-2

50 μm

D-2

50 μm

C-2

50 μm

• A and C survived 70 and 1022 cycles, respectively. • B and D survived 2000 cycles, showing a superior stability. (a) B and D

showed vertical cracks during JETS test; (b) buffer layer(s); and (c) composite coats.

67

Composite coating with double buffer layers

50μm 50μm50μm 50μm

(b) (c) (d)(a)

(a) as-coated (b) after FCTF (c) after TS (d) after JETS


68

Vicker’s hardness of composite coating with double buffer layers

0

1

2

3

4

5

6

After FCTF test

Har

dnes

s (G

Pa)

Buffer layer top coatYSZ + La2Zr2O7 composite top coat

Bond coat

After TS test After JETS testAs-prepared

• In general, hardness increased due to densification in top coat and buffer layer, and oxidation of bond coat.

69

Summary• La2Zr2O7 powder and coating microstructure and chemistry

characterizations show that La2Zr2O7 is stable at high temperatures, which makes it suitable for TBC applications.

• Mechanical properties (hardness, bond strength) are similar to 8YSZ.

• Thermal conductivity of La2Zr2O7 is lower than 8YSZ of similar porosity.

• Thermal properties using MD and image-based FE models calculations are in good agreement with experiments.

• Composite coatings and buffer layer are effective in improving the thermal durability of La2Zr2O7 TBCs.

• TBC with double buffer layers showed the most outstanding thermal durability in all tests.

70

Future workThermal stability of La2Zr2O7 coatings can be further improved by microstructure design using composite coating and buffer layers.

71

Publications and presentations1. Xingye Guo, Linmin Wu, Yi Zhang, Yeongil Jung, Li Li, James Knapp, and Jing Zhang, Carbon Dioxide

Adsorption on Lanthanum Zirconate Nanostructured Coating Surface: A DFT Study, Adsorption, 22(2), pp 159-163, 2016

2. Xingye Guo, Zhe Lu, Yeongil Jung, Li Li, James Knapp, and Jing Zhang, Thermal properties, thermal shock and thermal cycling behavior of lanthanum zirconate based thermal barrier coatings, Metallurgical and Materials Transactions E, (DOI: 10.1007/s40553-016-0070-4)

3. Xingye Guo, Linmin Wu, Yi Zhang, Yeongil Jung, Li Li, James Knapp, and Jing Zhang, First Principles Study of Nanoscale Mechanism of Oxygen Adsorption on Lanthanum Zirconate Surfaces, Physica E, (DOI: 10.1016/j.physe.2016.04.012)

4. Xingye Guo, Bin Hu, Changdong Wei, Jiangang Sun, Yeon-Gil Jung, Li Li, James Knapp, and Jing Zhang, Image-Based Multi-Scale Simulation and Experimental Validation of Thermal Conductivity of Lanthanum Zirconate, International Journal of Heat and Mass Transfer, (DOI:10.1016/j.ijheatmasstransfer.2016.04.067)

5. Dowon Song, Ungyu Paik, Xingye Guo, Jing Zhang, Zhe Lu, Je-Hyun Lee, Yeon-Gil Jung,Microstructuredesign for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings, 2016 International Conference on Metallurgical Coatings and Thin Films (ICMCTF 2016), San Diego, CA, USA, April 25-29, 2016

6. Xingye Guo, Zhe Lu, Yeon-Gil Jung, Li Li, James Knapp, Jing Zhang, Thermal and mechanical properties of novel lanthanum zirconate based thermal barrier coatings, 2016 International Thermal Spray Conference (ITSC 2016), Shanghai, China, May 10 - May 12, 2016

7. Sung Hoon Jung, Zhe Lu, Seung Soo Lee, Yeon Gil Jung, Jing Zhang, Ungyu Paik, Microstructure design and thermal durability of Yb-Gd-YSZ thermal barrier coatings in cyclic thermal exposure, 2016 International Thermal Spray Conference (ITSC 2016), Shanghai, China, May 10 - May 12, 2016

8. XingyeGuo, LinminWu, Yi Zhang, Yeon-Gil Jung, Li Li, James Knapp, Jing Zhang, Tensile Strength, Shear Strength and Adhesion Energy of Al2O3(0001) / Ni(111) Interface: A First Principles Study, Materials Science & Technology 2016 (MS&T16), Salt Lake City, UT, USA, October 23-27, 2016

72

9. Xingye Guo, Zhe Lu, Sung-Hoon Jung, Yeon-Gil Jung, Li Li, James Knapp, Jing Zhang, Microstructure Design of Novel Composite Lanthanum Zirconate-Yttria Stabilized Zirconia Based Thermal Barrier Coatings, Materials Science & Technology 2016 (MS&T16), Salt Lake City, UT, USA, October 23-27, 2016

10. Xingye Guo, Zhe Lu, Sung-Hoon Jung, Yeon-Gil Jung, Li Li, James Knapp, Jing Zhang, Thermal and mechanical properties of novel multi-layer lanthanum zirconate based thermal barrier coatings, Materials Science & Technology 2016 (MS&T16), Salt Lake City, UT, USA, October 23-27, 2016

11. Yi Zhang, Eun-Hee Kim, Geun-Ho Cho, Yeon-Gil Jung, Jing Zhang, Modeling mechanical properties of amorphous Na2O-SiO2 systems for high-temperature sand mold and core materials, Materials Science & Technology 2016 (MS&T16), Salt Lake City, UT, USA, October 23-27, 2016

12. Jing Zhang, Microstructure Design and Performance of Lanthanum Zirconate Based Thermal Barrier Coatings, Department of Materials Science, Purdue University, November 6, 2015

13. Xingye Guo, Jing Zhang, Yeon-Gil Jung, Li Li, James Knapp, Carbon Dioxide Adsorption on Nanostructured Lanthanum Zirconate Surface: A DFT study, IUPUI Nanotechnology Research Forum and Poster Symposium, Indianapolis, IN, October 23, 2015

14. Xingye Guo, Jing Zhang, Novel Lanthanum Zirconate Thermal Barrier Coatings For Gas Turbines, The Joint Board of Advisors Meeting, IUPUI, October 13th, 2015

15. Yeon-Gil Jung, Jing Zhang, Microstructure Design of Lanthanum Zirconate Coatings and Its lifetime Performance, The MS&T 2015, Material Science & Technology Conference and Exhibition, October 4 -October 8, 2015, Columbus, OH

16. Xingye Guo, Jing Zhang, Zhe Lu, Yeon-Gil Jung, Thermal Gradient Mechanical Fatigue Study of Lanthanum Zirconate Thermal Barrier Coatings, The MS&T 2015, Material Science & Technology Conference and Exhibition, October 4 - October 8, 2015, Columbus, OH

17. Xingye Guo, Jing Zhang, Density Functional Theory Study of Gas Adsorption on Lanthanum ZirconateNanostructured Coating Surface, The MS&T 2015, Material Science & Technology Conference and Exhibition, October 4 - October 8, 2015, Columbus, OH

18. Yi Zhang, Jing Zhang, Sintering of Nanostructured Zirconia: A Molecular Dynamics Study,The MS&T 2015, Material Science & Technology Conference and Exhibition, October 4 - October 8, 2015, Columbus, OH

73

19. Dowon Song, Ungyu Paik, Jing Zhang, Zhe Lu, Je-Hyun Lee, Yeon-Gil Jung, Microstructure Design and Thermal Durability of Lanthanum Zirconate Based Thermal Barrier Coatings, 7th Asian Thermal Spray Conference (ATSC2015), Xi'an, China, September 23-25, 2015

20. Zhe Lu, Je-hyun Lee, Yeon-Gil Jung, Jing Zhang, Dowon Song, Ungyu Paik, Microstructure Evolution and Durability of Thermal Barrier Coatings in Thermally Graded Mechanical Fatigue Environments, 7th Asian Thermal Spray Conference (ATSC2015), Xi'an, China, September 23-25, 2015

21. Jing Zhang, Advanced Materials Research, Argonne National Laboratory, September 11, 201522. Yeon-Gil Jung, Zhe Lu, Ungyu Paik, and Jing Zhang, Lifetime Performance of Thermal Barrier Coatings in

Thermally Graded Mechanical Fatigue Environments, The 11th International Conference of Pacific Rim Ceramic Societies(PacRim-11), Jeju, Korea, August 30 - September 4, 2015

23. Yeon-Gil Jung, Zhe Lu, Qi-Zheng Cui, Sang-Won Myoung, and Jing Zhang, Thermal Durability and Fracture Behavior of Thermal Barrier Coatings in Thermally Graded Mechanical Fatigue Environments, the International Symposium on Green Manufacturing and Applications 2015 (ISGMA 2015), Qingdao, China, June 23 - June 27, 2015

24. Jing Zhang, Yeon-Gil Jung (eds.), 1st International Joint Mini-Symposium on Advanced Coatings, Materials Today: Proceedings, 2014

25. Xingye Guo, Jing Zhang, Zhe Lu, Yeon-Gil Jung, Theoretical prediction of thermal and mechanical properties of lanthanum zirconate nanocrystal, the 1st International Conference & Exhibition for Nanopia, Changwon Exhibition Convention Center, Gyeongsangnam-do Province, Miryang City, Korea, November 13-14, 2014

26. Sang-Won Myoung, Zhe Lu, Qizheng Cui, Je-Hyun Lee, Yeon-Gil Jung, Jing Zhang, Thermomechanical properties of thermal barrier coatings with microstructure design in cyclic thermal exposure, the 1st International Conference & Exhibition for Nanopia, Changwon Exhibition Convention Center, Gyeongsangnam-do Province, Miryang City, Korea, November 13-14, 2014

27. Zhang, J., X. Guo, Y.-G. Jung, L. Li, and J. Knapp, Microstructural Non-uniformity and Mechanical Property of Air Plasma-sprayed Dense Lanthanum Zirconate Thermal Barrier Coating. Materials Today: Proceedings, 2014. 1(1): p. 11-16.

28. Guo, X. and J. Zhang, First Principles Study of Thermodynamic Properties of Lanthanum Zirconate. Materials Today: Proceedings, 2014. 1(1): p. 25-34.

novel functional graded thermal barrier coatings in coal-fired

Documents