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!