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Effects of Microstructures on Radiative
Properties of YSZ Thermal Barrier Coatings
Bo-Xiang Wang
School of Mechanical Engineering
Shanghai Jiao Tong University
Email:[email protected]
16th CSS-EEST, Nov. 13-15, 2014
Outline
Background: Thermal barrier coatings
Simulation and experimental methods
Microstructural effects on radiative properties
Temperature distribution across thermal barrier
Heat conductivity of EB-PVD YSZ coating as a function
of temperature
Thermal Barrier Coatings
The microstructures of Air Plasma Sprayed (APS) and EB-PVD
thermal barrier coatings
Standard thermal barrier coatings have a typical porosity of 10–20%
SEM micrographs of fracture surfaces of as-sprayed YSZ top coats
MATERIALS
Nowadays Typical state-of-the-art TBCs utilize ZrO2 partially with 6-8 wt% Y2O3
Table 1.Thermal physical properties and electromagnetic performance parameter of ZrO2
Name Value SI unit
6.0
2700
4300
0.2~3.5
86
12.5 ~
Refractive index n 2.1 ~
θ
a
b
mic-crack
void
pore
Simulated Structures
Simulation Methods
Plane wave source
TBC coating
Per
iod
ical
bound
ary c
ondit
ion
Per
iod
ical
bound
ary c
ondit
ion
PML obsorbing boundary condition
PML obsorbing boundary condition
-ln( ( ) / (0)) -ln( ( ))I L I LK
L L
ln( ( ) / (0)) ln( ( ))I L I LK
L L
0 r
EH
t
0
HE
t
Maxwell’s equations Extinction coefficient
Measurement principle of hemispherical transmittance/reflectance
Measurement principle
1 2 3 4 5 6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Tra
nsm
itta
nce
Wavelength (m)
Experimental data
Calculated data
Experimental data vs. simulation results
Experimental data: thickness=200μm, porosity=15%
Simulation data: 10% spherical pores (radius=1μm) and 5% cracks (a=1 μm,b=5 μm)
1 2 3 4 5 6
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
Exti
nct
ion c
oef
fici
ent
K (
1/m
)
Wavelength (m)
random arrangement
regular arrangement
Extinction coefficient of coating for different arrangement of spherical pores
Microstructural effect on the radiative properties
1 2 3 4 5 6
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10000
porosity=20%
porosity=15%
Exti
nct
ion c
oef
fici
ent
1
/m)
Wavelength (m)
porosity=5%
porosity=10%
(a)5 10 15 20
3000
4000
5000
6000
7000
8000
9000
Tota
l ex
tinct
ion c
oef
fici
ent
K (
1/m
)
Porosity (%)(b)
Extinction coefficient of the coating for different porosity
Microstructural effect on the radiative properties
0 1 2 3 4 5 6 7
2000
3000
4000
5000
6000
7000
8000
9000
10000
Exti
nct
ion c
oef
fici
ent
(1/m
)
Wavelength (m)
r=0.3m
r=0.5m
r=1m
r=1.5m
(a)
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
4500
5000
5500
6000
6500
7000
7500
8000
pore radius (m)
Tota
l ex
tinct
ion c
oef
fici
ent
(1/m
)
(b)
Extinction coefficient of the coating for different pore radius
Microstructural effect on the radiative properties
a b
a
a
a
b
b
b
b/a=1
b/a=2
b/a=4
b/a=6
(a)
θ
(b)
Schematic of microstructures with different shapes (a), and orientations (b)
Microstructural effect on the radiative properties
1 2 3 4 5 6
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
Exti
nct
ion c
oef
fici
ent
(1/m
)
Wavelength (m)
b/a=1
b/a=2
b/a=4
b/a=8
b/a=12
a=0.5m
(a)0 2 4 6 8 10 12
3000
4000
5000
6000
7000
8000
9000
Tota
l ex
tinct
ion c
oef
fici
ent
(1/m
)
Shape coefficient b/a(b)
Extinction coefficient of the coating for different microstructure shape
Microstructural effect on the radiative properties
0 1 2 3 4 5 6
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
Exti
nct
ion c
oef
fici
ent
(1/m
)
Wavelength (μm)
=0
=30
=60
=90
(a)0 30 60 90
2000
4000
6000
8000
10000
12000
Tota
l ex
tinci
ton c
oef
fici
ent
(1/m
)Orientation ()(b)
Extinction coefficient of the coating for different orientations
Microstructural effect on the radiative properties
Many thanks for your attention!
