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
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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
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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)
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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
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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
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Outline• Introduction• Coating design and fabrication
• Single ceramic layer (SCL) – Dense Coat• 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
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.
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■ : 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)
5279-13 line #1 5279-14 line #2 5279-15 line #3 5279-17 line #5 5279-18 line #6
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)
5279-13 line #1 5279-14 line #2 5279-15 line #3 5279-17 line #5 5279-18 line #6
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]
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Outline• Introduction• Coating design and fabrication
• Single ceramic layer (SCL) – Porous Coat• 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
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
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40
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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
Outline• Introduction• Coating design and fabrication
• Double ceramic layer (DCL) coats• 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
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
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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
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
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
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
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)
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)
45
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
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
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
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
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 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
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
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)
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
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
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)
La2Zr2O7 (50 vol%) +
8YSZ (50 vol%)coat
Substrate
Porous YSZ coat
370μm
B
120 μm
Bond coat (NiCrAlY[1])
La2Zr2O7 (75 vol%) +
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)
La2Zr2O7 (25 vol%) +
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
)
InterfaceTop coat Bond coat0
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
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
10 cycles/Fully delaminated
70 cycles/Fully delaminated
(B) DLC TBC (50% LZ : 50 % YSZ
in volume) with single buffer layer
768 cycles/Fully delaminated
29 cycles/Fully delaminated
2000 cycles/Sound condition
(C) SLC TBC (25% LZ : 75 % YSZ
in volume)
936 cycles/Fully delaminated
14 cycles/Fully delaminated
1022 cycle/Fully delaminated
(D) DLC TBC (50% LZ : 50 % YSZ
in volume) with double buffer layers
1143 cycles/Sound condition
54 cycles/Partially delaminated
2000 cycles/Sound condition
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
Song, et al., Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings, ICMCTF 2016
• 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
Song, et al., Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings, ICMCTF 2016
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.