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Reaction of Lanthanide ZirconatePyrochlore Environmental Barrier

Coating Materials in CMAS

Jeffrey W. Fergus

2015 Crosscutting Research ReviewPittsburgh, PA28 April 2015

Participants

• Auburn University– Jeff Fergus – Honglong (Henry) Wang – Ph.D. Student– Xingxing Zhang – Ph.D. Student– Emily Tarwater – Undergraduate Student– Sudip Dasgupta – Visiting Scholar (Summer 2014)

• Plasma Processes LLC– Kyle Murphree– Tim McKechnie

28 April 2015 CCR 2015

Bond coat system

28 April 2015 CCR 2015

• Collaboration with Plasma Processes LLC

• Alternative bond coat layers• YSZ / zirconate coatings

http://www.plasmapros.com/

Thermal barrier coating system

TBC: YSZ and/or pyrochlore

Alloy: 738LC

Ir (50-100 μm)Re diffusion layer

Hf (25-50 μm)

Flash Ni coating

28 April 2015 CCR 2015

Plasma spray for YSZ / pyrochlore

Molten salt electrochemical deposition (El-Form®) for Re/Hf/Ir

Approach

• Coating development– Evaluate need for Ni coating– Optimize Hf/Ir for YSZ – Feasibility Hf/Ir for pyrochlore– YSZ + pyrochlore

• Coating materials– Stability of pyrochlore in CMAS

• Gd2Zr2O7, Sm2Zr2O7, mixed

– Accelerate with high temperature exposures

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Need for nickel layer

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TBC: YSZ and/or pyrochlore

Alloy: 738LC

Ir (50-100 μm)Re diffusion layer

Hf (25-50 μm)

Flash Ni coatingEvaluate possible elimination of Ni coating

?

Rhenium coating with/without nickel

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With Ni LayerWithout Ni Layer

Nickel coating needed

Iridium coatings on round samples

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2 out of 20 iridium coatings good quality

Electrochemical deposition reveals non-

visible defects in Re coating

Iridium coatings on rectangular samples

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Rectangular coatings for mechanical testing

Revised approach

• Electrochemical deposition process sensitive to defects in substrate coating

• Focus coating efforts on environmental barrier coatings

• Plasma-sprayed materials to corroborate results from sintered ceramics

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Pyrochlore coating materials

• Reaction with CMAS• Thermal conductivity

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Reaction with CMAS

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La2Zr2O7

YSZ + La2Zr2O7

YSZ

C.S. Ramachandran et al., Ceram. Int. 39, 1413 (2013)

Thermal conductivity of zirconia with 7-8% yttria

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

200 400 600 800 1000 1200 1400 1600

[ 13 ] [ 13 ] [ 14 ] [ 14 ] [ 15 ] [ 16 ]

[ 17 ] [ 18 ] [ 19 ] [ 20 ] [ 21 ] [ 21 ]

[ 21 ] [ 22 ] [ 23 ] [ 23 ] [ 23 ] [ 24 ]

[ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 29 ] [ 30 ]

Temperature (K)

Thermalcond

uctiv

ity (W

m‐1K‐

1 )

Range of thermal conductivities due to variations in morphology and microstructure

28 April 2015 CCR 2015

J. Fergus. Met. Mater. Trans E 1, 118 (2014).

Thermal conductivity of Gd2Zr2O7

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

200 400 600 800 1000 1200 1400 1600

[ 16 ] [ 18 ] [ 55 ]

[ 56 ] [ 56 ] [ 58 ]

[ 59 ] [ 60 ] [ 61 ]

Temperature (K)

Thermalcond

uctiv

ity (W

m‐1K‐

1 )

7‐8 wt% YSZ from Figure 1 κ of Gd2Zr2O7

in lower range of YSZ

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Thermal conductivity of Sm2Zr2O7

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

200 400 600 800 1000 1200 1400 1600

[ 16 ] [ 56 ]

[ 56 ] [ 61 ]

[ 62 ] [ 63 , 64 , 65 ]

[ 66 ] [ 67 ]

Temperature (K)

Thermalcond

uctiv

ity (W

m‐1K‐

1 )

7‐8 wt% YSZ from Figure 1 κ of Sm2Zr2O7

in lower range of YSZ

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Ytterbium-doping

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

200 400 600 800 1000 1200 1400 1600

0 Yb0.1 Yb0.3 Yb0.5 Yb

Temperature (K)

Thermalcond

uctiv

ity (W

m‐1K‐

1 )

(Gd1‐xYbx)Zr2O7

Increasing Yb

7‐8 wt% YSZ from Figure 1

Gd2Zr2O7from Figure 7

Sm2Zr2O7from Figure 8

Doping can reduce κ

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Thermal conductivity of mixed pyrochlores

1.4

1.6

1.8

2.0

2.2

2.4

2.6

0.0 0.2 0.4 0.6 0.8 1.0

[ 55 ] [ 66 ]

Thermalcond

uctiv

ity (W

m‐1K‐

1 )

x

(La1‐xGdx)Zr2O7

(Sm1‐xYbx)Zr2O7

Pyrochloresolid solutions have lower κ

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Pyrochlore coating materials

• Synthesis of pyrochlore– Co-precipitation

• CMAS exposure– Melt / solidify Ca-Mg-Al-Si oxide

mixtures– Crush glass, apply to pyrochlore pellet– Expose to 1200-1400°C

• Characterization– XRD, SEM, optical microscopy

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CMAS CompositionOxide PercentageCaO 33MgO 9AlO1.5 13SiO2 45

Microstructure of Gd2Zr2O7

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Co-precipitation

Phase content of Gd2Zr2O7

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30 40 50 60 70 80 90

(511

)

(531

)

(840

)(6

62)

(800

)

(444

)(6

22)

(440

)

(331

)(400

)

(222

)

1500C 5h

1400C 10h

1400C 5h

Inte

nsity

(A.U

.)

2

Pyrochlore

Gd2Zr2O7 after CMAS at 1400°C for 5 hours

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30 40 50 60 70 80 90

****

P(511)P(331)

P(511)P(331)

PPPP

PP

P

P

PPPP

PPP

PFFFF

FFF

2Before corrosion

Non-contacted surface

CMAS contacted surface

Inte

nsity

(A.U

.)

F

* Ca2Gd8(SiO4)6O2

# Gd2Si2O7P Pyrochlore Gd2Zr2O7F Fluorite structure

Pyrochlore

Fluorite


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30 40 50 60 70 80 90

# ## *****

P(511)P(331) PPPP

PP

P

P

PPPP

PP

P(511)P(331)P

F

FFFFF

FF

* *****

2Before corrosion



Inte

nsity

(A.U

.)

*

* Ca2Gd8(SiO4)6O2

P

# Gd2Si2O7

P Pyrochlore Gd2Zr2O7F Fluorite structure

Pyrochlore

Fluorite


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28 April 2015 CCR 2015


Ca2Gd8(SiO4)6O2

Gd2Zr2O7 after CMAS at 1300°C for 15 minutes + 1200°C for 30 hours

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Concentration

# O Mg Al Si Ca Zr Gd Au1 62 - - 14 5 - 15 42 60 2 4 12 5 - 13 4

Gd silicate


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Concentration

# O Mg Al Si Ca Zr Gd Au1 56 - - 14 6 1 17 52 63 - 3 12 5 1 13 43 67 - 1 12 4 1 12 34 64 - 1 1 5 - 13 4

Gd silicate


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Concentration

# O Mg Al Si Ca Zr Gd Au1 60 1 1 1 2 27 5 42 67 - 1 1 2 23 4 33 61 - 1 2 2 25 6 4

Cubic fluorite


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Concentration

# O Mg Al Si Ca Zr Gd Au1 59 - - - - 17 18 52 65 - - - - 18 17 -

Pyrochlore

Gd2Zr2O7 after CMAS at 1200°C

28 April 2015 CCR 2015

Concentration# Mg Al Si Ca Zr Gd1 0 0 15 7 9 142 0 0 15 6 11 203 0 0 14 6 7 124 0 0 2 2 33 55 0 0 2 3 34 76 0 0 2 2 29 5


40 hours 60 hours

Gd2Zr2O7 after CMAS at 1200°C – 60 hours

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Gd+Zr

CMAS

ZrO2-Gd2O3phase diagram

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T = tetragonalF = cubic fluoriteM – monoclinicP = pyrochloreC, B, H = Gd2O3 phases

Microstructure of Sm2Zr2O7

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1μm

Figure 2. Surface morphology of Sm2Zr2O7, sintered at 1500°C for 5h.

Phase content of Sm2Zr2O7

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30 40 50 60 70 80 90

1500C 5h

1400C 15h

1400C 10h

(511

)

(311

)

(840

)(6

62)

(800

)

(444

)(6

22)

(440

)

(331

)(440

)

Inte

nsity

(A.U

.)

2

(222

)

1400C 5h

Sm2Zr2O7 after CMAS at 1400°C for 5 hours

28 April 2015 CCR 2015

30 40 50 60 70 80 90

****

P(511)P(331)

P(511)P(331)

PPPP

PP

P

P

PPP P

PPP

P

FFFFFFF

2

Before Corrosion

Non-contactedsurface


* Ca2Sm8(SiO4)6O2

P Pyrochlore Sm2Zr2O7F Fluorite Sm2Zr2O7

Inte

nsity

(A.U

.)

F

*


28 April 2015 CCR 2015

30 40 50 60 70 80 90

*****

P(331)

P(511)

P(511)

PPPP

PP

P

P

PPPP

PP

P(331)

P

P

FFFFFF

F

F

Inte

nsity

(A.U

.)

2

Before corrosion



* Ca2Sm8(SiO4)6O2

P Pyrochlore Sm2Zr2O7F Fluorite Sm2Zr2O7

*


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10μm

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Sm2Zr2O7 after CMAS at 1300°C for 15 minutes + 1200°C for 30 hours

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Concentration

# O Mg Al Si Ca Zr Gd Au1 47 1 8 20 11 2 8 32 60 3 10 18 7 1 1 23 58 1 5 16 9 1 7 34 53 6 5 17 18 - - 25 54 4 7 17 13 - 1 26 55 3 10 19 10 1 1 2

1,3: Bright spotsSm silicate


28 April 2015 CCR 2015

Concentration

# O Mg Al Si Ca Zr Gd Au1 62 - 1 1 2 27 4 32 66 - - 1 2 25 3 33 58 2 5 7 10 13 3 34 65 1 2 3 5 18 4 2

Cubic fluorite


28 April 2015 CCR 2015

Concentration

# O Mg Al Si Ca Zr Gd Au1 47 - - 10 6 6 23 92 44 - - 2 4 38 7 53 51 - - 7 7 15 15 54 54 - - 2 3 31 6 45 40 - - 8 7 12 26 96 53 - 1 4 4 26 7 5

1,3,5: Sm silicate2,4,6: Cubic fluorite


28 April 2015 CCR 2015

Concentration

# O Mg Al Si Ca Zr Gd Au1 67 - 1 - - 18 12 22 72 - - 1 - 17 7 33 68 - - - - 19 13 -4 65 - - - - 18 15 35 66 - - 1 - 18 12 3

Pyrochlore

Sm2Zr2O7 after CMAS at 1200°C – 60 hours

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Sm2Zr2O7 after CMAS at 1200°C – 60 hours

28 April 2015 CCR 2015

CMAS

Sm + Zr

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T = tetragonalF = cubic fluoriteM – monoclinicPyr = pyrochloreC, B, H = Sm2O3 phases

ZrO2-Sm2O3phase diagram

(Gd,Sm)2Zr2O7 after CMAS at 1200°C for 60 hours

28 April 2015 CCR 2015

(Gd0.8Sm0.2)2Zr2O7 (Gd0.6Sm0.4)2Zr2O7

Concentration# Mg Al Si Ca Zr Sm Gd1 0 0 14 5 5 10 02 0 0 19 7 6 17 03 0 0 17 6 8 14 04 0 0 17 6 8 14 15 0 0 1 3 41 5 06 0 0 3 3 46 6 07 0 0 2 3 45 6 0

Concentration# Mg Al Si Ca Zr Sm Gd1 0 0 17 7 6 6 92 0 0 15 10 9 10 143 0 0 13 5 4 4 64 0 0 1 3 35 1 35 0 0 1 2 36 2 36 0 0 1 3 39 2 4

Conclusions• Coatings

– Ni flash coating needed to obtain quality Re coating– Only 2 out of 20 Ir coatings on Re-coatings round

samples were successful– No Ir coatings on rectangular samples were

successful• EBC materials

– Reaction of Gd2Zr2O7, Sm2Zr2O7 and (Gd,Sm)2Zr2O7with CMAS evaluated

• Pyrochlore dissolves in CMAS• Reprecipitates as lanthanide silicate and cubic fluorite phase

28 April 2015 CCR 2015