Novel Functional Graded Thermal Barrier Coatings in Coal-fired … · 2015. 4. 28. · Novel Functional Graded Thermal Barrier Coatings in Coal-fired Power Plant Turbines Jing Zhang

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

2015 NETL Crossingcutting Research Review Meeting, Pittsburgh, PA, April 27-30, 2015

2

Acknowledgement

• Subcontract: James Knapp (Praxair Surface Technologies)• Collaborators: Li Li, Don Lemen (Praxair Surface

Technologies)• Yeon-Gil Jung (Changwon National 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 fabrications• Single ceramic layer (SCL) architecture• Double ceramic layer (DCL) architecture• Characterization of physical and mechanical properties• Microstructure and composition• Porosity and hardness• Bond strength test• Erosion test

• Characterization of thermal properties• Thermal conductivity and specific heat measurements• Jet engine thermal shock tests• Thermal gradient mechanical fatigue tests

• Summary and future work

4

Limitation of yttria stabilized zirconia

• Zirconia partially stabilized with 7 wt% yttria (7YSZ) is the current state-of-the-art thermal barrier coating material.

• However, at temperatures higher than 1200 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 temperature of turbine engines, alternative TBC materials with lower thermal conductivity, higher operating temperatures and better sintering resistance are required.

• The objective of the project is to develop a novel lanthanum zirconate based multi-layer thermal barrier coating system.

• The ultimate goal is to develop a manufacturing process to produce pyrochlore oxide based coating 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?

• Higher temperature phase stability. No phase transformation

• Lower sintering rate at elevated temperature

• Lower thermal conductivity• Lower CTE

Phase diagram of La2O3–ZrO2

Compared with YSZ, La2Zr2O7 has

8

La2Zr2O7 vs. YSZ

Materials property 8YSZ La2Zr2O7Melting Point (oC) 2680 2300Maximum Operating Temperature (oC) 1200 >1300Thermal Conductivity (W/m-K) (@ 800oC )

2.12 1.6

Coefficient of Thermal Expansion (x10-6/K) (@1000 oC)

11.0 8.9-9.1

Density (g/cm3) 6.07 6.00Specific heat (J/g-K) (@1000 oC) 0.64 0.54

9

Layered coating architecture

• The coefficient of thermal expansion of La2Zr2O7(10x10-6 /oC) is lower than those of both substrate and bondcoat (about 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 a multi-layer, functionally graded, pyrochlore oxide based TBC system

10

La2Zr2O7 spray powder morphology Powder surface morphology

•Spherical shape with a rough surface•Good flowability and high density•Particle size between 30 ~ 100 m

+ 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, NetherlandsK1 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)

13

Synchrotron XRD

In situ Synchrotron XRD shows no compositional change at high temperatures

Wavelength 0.108 Å

2 (o)

Cou

nt (a

.u.)

credit: Yang Ren @ ANL

14

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

15

Outline• Introduction• Coating fabrications• Single ceramic layer (SCL) architecture – dense coating• Double ceramic layer (DCL) architecture• Characterization of physical and mechanical properties• Microstructure• Hardness and Young’s modulus• Bond strength test• Erosion test

• Characterization of thermal properties• Thermal properties• Jet engine thermal shock tests• Thermal gradient mechanical fatigue tests


16

Cross sectional view of dense coating 1 2 3

4 5 6

Processing parameters (powder feed rate, surface speed, current, stand off ) were varied to control the porosity.

17

200 400 600 800 1000 1200 1400 1600 1800 2000 22000

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

■ : 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)


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)


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]

22

Outline• Introduction• Coating fabrications• Single ceramic layer (SCL) architecture – porous coating• Double ceramic layer (DCL) architecture• Characterization of physical and mechanical properties• Microstructure and composition• Porosity and hardness• Bond strength test• Erosion test



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

27

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

240

0 500 1000 1500 2000 25000

20

40

60

80

100

120

140

160

180

200

220

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




32

Double ceramic layer (DCL) architectures

Bond coat (NiCrAlY)

Porous La2Zr2O7 top

coat

Substrate (Haynes‐188)

432μm

228 μm 1

27 μ

m

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

33

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

Heat treatment1080 4h

Ar atmosphere

LD La2Zr2O7, 12 mils

LD 8YSZ, 5 mils

35

Vickers hardness of DCL

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

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

37

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

1

ni i

si s s

E t TE t

11

22

ns i i

i ii s s

t E t h tE t

21

6n i ii s s

E t TKE t

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 z i i iE K z

X.C. Zhang, Thin Solid Films, 488 (2005) 274-282.

where

38

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

39

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 3/2105IC

critE KV

H R

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

40

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 (g/g)

● Sample 1 ▲ Sample 2■ Sample 3◆ Sample 4

6789

41




42

Thermal conductivity

Thermal 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

43

Thermal conductivity and heat capacity map

TBC is 90.55% dense (=5.478g/cc), with a nominal thickness of 600mIndentation marks are from previous study

credit: Jiangan Sun @ ANL

44

TBC: Material: La2Zr2O7Thickness: ~600m (this is used in calculation)Density: 90.55% dense, dense density=6 g/cc, so density = 5.478 g/ccSpecific heat: c = 0.54 J/g-K @1000C

Substrate (following are room temperature properties obtained from matweb):Material: Haynes 188Density: = 8.98 g/ccThermal conductivity: k = 10.4 W/m-K,Specific heat: c = 0.403 J/g-K, (therefore, c = 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

Thermal conductivity and heat capacity map

45

Measured TBC thermal properties

Predicted average TBC properties (within red rectangular area): k = 0.55 W/m-K, c = 2.16 J/cm3-K

Thermal conductivity k image Heat capacity c image

0 1 W/m-K 0 2.5 J/cm3-K

These results were based on a TBC thickness of 600 m TBC specific heat @RT: c = 0.393 J/g-K; predicted TBC density is: =c/c=2.16/0.393=5.5 g/cc

credit: Jiangan Sun @ ANL

46

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)

47

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.

48

Jet engine thermal shock test (JETS) results

#6, Single layer La2Zr2O7 #7, Porous 8YSZ

#8, Porous 8YSZ+ La2Zr2O7 #9, Dense 8YSZ+ La2Zr2O7

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50

Tem

prea

ture

diff

eren

ce (F

)

Cycles

#6-A

#6-B

#6-C

#7-A

#7-B

#7-C

49

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

50

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.

51

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

52

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Ther

mal

con

duct

ivity

(W/m

/o C)

Temperature (oC)

Experiment Calculation

Imaged based FEM calculation of thermal conductivity of La2Zr2O7 coating

Calculated thermal conductivity 0.60±0.08 W/m-K, in good agreement with experimental data.

53

Summary• La2Zr2O7 powder, 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 ab initio and image-based finite element model calculations are in good agreement with experiments.

• Thermal cycling behavior of La2Zr2O7 needs to be improved.

Future work

54

Composite coatings with buffer layers

Bond coat (NiCrAlY)

La2Zr2O7 (50 vol%) +

8YSZ (50 vol%)coat

Substrate

430μm

1

60 μ

m

Bond coat (NiCrAlY)


8YSZ (50 vol%)coat

Substrate

Porous YSZ coat

370μm

1

120 μm

Bond coat (NiCrAlY[1])


8YSZ (25 vol%)coat

Substrate

310μm

2

LZ (25)+YSZ (75)

Porous YSZ coat

60 μm

Composite top coats:thermal conductivity + matching CTEs

Introducing buffer layer:Increasing strain compliance + Decreasing CTEs mismatch

2nd buffer layer:Further decrease CTEs mismatch

Bond coat (NiCrAlY)


8YSZ (75 vol%)coat

Substrate

430μm

2

55

Publications and presentations1. Jing Zhang, Yeon-Gil Jung, Li Li, co-organize “Advanced Coating Materials for Energy and

Environmental Applications” symposium in Materials Science & Technology 2015 (MS&T15), October 4-8, 2015, Columbus, OH

2. Jing Zhang, Yeon-Gil Jung (eds.), 1st International Joint Mini-Symposium on Advanced Coatings, Materials Today: Proceedings, 2014

3. 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

4. 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

5. 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

6. 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

7. 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.

8. Guo, X. and J. Zhang, First Principles Study of Thermodynamic Properties of Lanthanum Zirconate. Materials Today: Proceedings, 2014. 1(1): p. 25-34.

Novel Functional Graded Thermal Barrier Coatings in Coal-fired … · 2015. 4. 28. · Novel Functional Graded Thermal Barrier Coatings in Coal-fired Power Plant Turbines Jing Zhang

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