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Development of Advanced Thermal Barrier Coatings by Plasma Spraying
High Temperature Thermo-Chemistry Laboratory&
Korea Institute of Materials Science
Date: 16th March 2021
Yeon Woo Yoo
High Temperature Thermochemistry Laboratory
2Contents
I. Introduction about Thermal Barrier Coatings
II. Development of Low-k Ceramic Top Coat by Suspension Vacuum Plasma Spraying
III. Development of Advanced Metallic Bond Coat by Vacuum Plasma Spraying
3
I. Introduction about Thermal Barrier Coatings
High Temperature Thermochemistry Laboratory
4Introduction
- Hot sections in industrial / aviation gas turbine(GT)
Tem
pera
ture
o C TIT(Turbine inlet temperature)1400 ~ 1600 oC
• Components in combustion chamber and turbine
• High temperature & oxidation environment
compression combustion
High Temperature Thermochemistry Laboratory
5Introduction
- Increment of turbine inlet temperature
• Efficiency of GT ↑ → TIT ↑
• Increment rate of TIT exceed increment of metal material temperature
→ Protective coating(thermal barrier coating) and cooling are required
High Temperature Thermochemistry Laboratory
6Introduction
• Top coat- Yttria stabilized zirconia (8YSZ), GZO(Gd2Zr2O7), LZO(La2Zr2O7)
- Thermal insulation from high temperature environment
- Low thermal conductivity and porous microstructure
• Bond coat- MCrAlX M= Ni and/or Co , X = Y, Ta, Hf, and/or Si, other minor
elements
- Intermediate thermal expansion coefficient between top coating and
bottom Ni based superalloys
- Directly related to the thermal lifetime of thermal barrier coatings
• Ni based superalloys- Maintain excellent mechanical strength at high temperature
(γ and γ` phase)
- Thermal barrier coatings (TBCs)
High Temperature Thermochemistry Laboratory
7Introduction
Lamellar structure Columnar structure
• Lower thermal conductivity• Poor thermal lifetime
→ Suitable for industrial gas turbine
• Excellent thermal lifetime• Higher thermal conductivity
→ Suitable for aviation gas turbine
- Two types of microstructures of TBCs
Jordan, Eric, and Gell, Maurice. Low Thermal Conductivity, High Durability Thermal BarrierCoatings for IGCC Environments. United States: N. p., 2015. Web. doi:10.2172/1182555.
1.942 1.876 1.256 0.800 0.176Calculated T/C
High Temperature Thermochemistry Laboratory
8Introduction
- Thermal spraying
9
II. Development of Low-k Ceramic Top Coat by Suspension Vacuum Plasma Spraying
*Low-k : Low thermal conductivity
High Temperature Thermochemistry Laboratory
10Introduction
• Particle sizes for suspension plasma spraying range from nanometer to sub micrometer
• Enable to melt completely high melting temperature powders
• Length of plasma flame increases as environment pressure decreases
- Suspension plasma spraying (SPS)
High Temperature Thermochemistry Laboratory
11Results
0 100 200 300 4000
5
10
15
20
25
0
5
10
15
20
Working pressure [ mbar ]
Form
atio
n ra
te [ µm
/min
]
Poro
sity
[ %
]
MCrAlY bond coating 50 μmMCrAlY bond coating 50 μm
MCrAlY bond coating
50 μm50 μm
• As increasing working pressure, coating formation rateand porosity of SVPS YSZ coating increased
Increasing working pressure
- Microstructures of SVPS YSZ coatings at various working pressure
High Temperature Thermochemistry Laboratory
12Results
20 30 40 50 60 70 80 90
Bond Coating
100 mbar
250 mbar
Inte
nsity
[ a.
u. ]
2theta [ degree ]
400 mbar
0 100 200 300 400 5000.0
0.5
1.0
1.5
2.0
Ther
mal
con
duct
ivity
[ W
/m K
]
Working pressure [ mbar ]
• Crystalline structure of SVPS YSZ coating did not changed as working pressure changed
• Thermal conductivity of SVPS YSZ coating decreased as working pressure decreased
t-ZrO2
- Crystalline structure and thermal conductivity of SVPS YSZ coatings at various working pressure
High Temperature Thermochemistry Laboratory
13Results
0 30 60 90 1200
200
400
600
800
1000
1200
Tem
pera
ture
[ o C
]
Time [ min ]APS 400 mbar 250 mbar
0
100
200
300
400
500
Ther
mal
Life
time
[ cyc
les
]
• SVPS YSZ coatings and APS YSZ coatings were evaluated thermal lifetimethrough furnace cyclic test (FCT)
• SVPS YSZ coatings showed better thermal lifetime than APS YSZ coatings
- Thermal lifetime evaluation and failure analysis of TBCs
High Temperature Thermochemistry Laboratory
14Results
- Low-k ceramic top coat by SVPS
20 30 40 50 60
SVPS GZO GZO Powder
Inte
nsity
[ a.
u. ]
2theta [ degree ]
Gd2Zr2O7 (GZO)
MCrAlY bond coat
Ni superalloy
• Pyrochlore oxides(A2B2O7) have low thermal conductivities than flurorite oxides(AO2) due to more phonon scattering
• Low-k pyrochlore oxide, Gd2Zr2O7(GZO) was formed on MCrAlY bond coat, however thickness was too thin to measure thermal conductivity of GZO layer.
High Temperature Thermochemistry Laboratory
15Summary
1. YSZ coatings were achieved by suspension vacuum plasma spraying at various working pressure
2. Lower thermal conductivity and longer thermal lifetime were achieved by SVPS
3. Low-k oxide(Gd2Zr2O7) were formed on MCrAlY bond coat and further analysis should be required
16
III. Development of Advanced Metallic Bond Coat by Vacuum Plasma Spraying
High Temperature Thermochemistry Laboratory
17Results
0 10 20 30 40 500
2
4
6
8
10
CoNiCrAlY NiCoCrAlY+Hf,Si NiCoCrAlY
Wei
ght c
hang
e [ %
]
Time [ hrs ]0 200 400 600 800 1000
13
14
15
16
17
18
19
20
21
NiCoCrAlY NiCoCrAlY + Hf,Si CoNiCrAlY
Ther
mal
Exp
ansi
on C
oeffi
cien
t [ 1
0-6 /
K ]
Temperature [ oC ]
• Thermal expansion analysis • STA analysis • Initial oxidation behavior
- Thermal properties analysis of bond coat alloys
*Conventional Ni superalloy ~14 ppm/KYttria stabilized zirconia < 10 ppm/K
High Temperature Thermochemistry Laboratory
18Results
- High temperature oxidation of bond coat alloys
0 200 400 600 800 1000-0.014
-0.012
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
0.002
∆(W
/ W
o)
Time [ hrs ]
NiCoCrAlY NiCoCrAlY + Hf,Si NiCoCrAlY + Ta IN7920 20 40 60 80 100
0.0000
0.0005
0.0010
0.0015
0.0020
∆(W
/ W
o)
Time [ hrs ]
NiCoCrAlY NiCoCrAlY + Hf,Si NiCoCrAlY + Ta IN792
1000 oC, air atmosphere
High Temperature Thermochemistry Laboratory
19Results
- EBSD analysis of bond coat alloys
NiCoCrAlY 1000 ℃
High Temperature Thermochemistry Laboratory
20Results
- Bond coat alloy design by thermodynamic calculation
FCC#1
FCC#1
BCC#1
BCC2#1
L12#1
HCP#1
Liquid
Co + Ni + Cr + Al + Y
Temperature [ oC ]
Wei
ght p
erce
nt [
% ]
600 700 800 900 1000 1100 1200 1300 1400 15000
10
20
30
40
50
60
70
80
90
100
1500
Hf2Ni7
Liquid
FCC#1
FCC#1
BCC#1
SIGMA
BCC2#1
BCC2#1L12#1
L12#1
Ni + Co + Cr + Al + Y + Hf + Si
Temperature [ oC ]
Wei
ght p
erce
nt [
% ]
600 700 800 900 1000 1100 1200 1300 14000
10
20
30
40
50
60
70
80
90
100
FCC#1
FCC#1
BCC#1
SIGMA
BCC2#1
BCC2#1L12#1
Liquid
Ni + Co + Cr + Al + Y
Temperature [ oC ]
Wei
ght p
erce
nt [
% ]
600 700 800 900 1000 1100 1200 1300 1400 15000
10
20
30
40
50
60
70
80
90
100
FCC#1
BCC#1
BCC2#1
L12#1
IN792 - NiCoCrAlY1000 oC
Wei
ght p
erce
nt [
% ]
IN792 NiCoCrAlY0
10
20
30
40
50
60
70
80
90
100
• Phase fractions of MCrAlY bond coats as function of a temperature
FCC#1
BCC2#1
IN792 - CoNiCrAlY1000 oC
Wei
ght p
erce
nt [
% ]
IN792 CoNiCrAlY0
10
20
30
40
50
60
70
80
90
100
• Secondary reaction expectation in interface between MCrAlY bond coats and Ni superalloys
Substrate SRZ Bondcoat
Ni, Ta, Re, etc.
Al, Cr, Co, Y
High Temperature Thermochemistry Laboratory
21Summary
1. Thermal properties were analyzed
2. Microstructure and crystalline structure of surface of metallic bond coat were analyzed after high temperature oxidation
3. Phase change at the surface and interface between bond coat and superalloys were analyzed by EBSD
4. Adoption of thermodynamic calculation could help with design of low oxidation and low diffusion bond coat
Thank you for
your attention!