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www.DLR.de Chart 1 >3rd Japanese-German TBC Workshop 27. June 2013 In-situ synchrotron X-ray strain measurements in TBC systems during thermal mechanical cycling M. Bartsch, J. Wischek, C. Meid German Aerospace Center, Cologne

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SLIDE 1

www.DLR.de • Chart 1 >3rd Japanese-German TBC Workshop • 27. June 2013

In-situ synchrotron X-ray strain measurements in TBC systems during thermal mechanical cycling

  • M. Bartsch, J. Wischek, C. Meid

German Aerospace Center, Cologne

  • A. M. Karlsson1, 2

former: 1Department of Mechanical Engineering, University of Delaware now: 2Fenn College of Engineering, Cleveland State University, Ohio

  • K. Knipe, A. Manero, S. Raghavan

Mechanical and Aerospace Engineering, University of Central Florida, Orlando, Florida

  • J. Okasinski, J. Almer

Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois

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SLIDE 2

Outline

www.DLR.de • Chart 2 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Motivation of the investigation
  • Experimental test facility at DLR and results
  • Numerical model and simulation results
  • Research objective and test set up at Argonne APS
  • Test configuration
  • Experiments and first results
  • Conclusions and project status
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SLIDE 3

Turbine blades in an aircraft engine

www.DLR.de • Chart 3 >3rd Japanese-German TBC Workshop • 27. June 2013

Rotating turbine blades

Engine Alliance GP7000

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SLIDE 4

Load and temperature cycle of a flight mission

www.DLR.de • Chart 4 >3rd Japanese-German TBC Workshop • 27. June 2013

Turbine entrance temperature (TET) time (min) 0 1 201 200 20 Rotational speed (rpm) Taxi Taxi Take

  • off

Climb Cruise Approach Thrust-reverse

→ very high heating and cooling rates during take off and after landing

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SLIDE 5

Turbine blades with protective coatings

www.DLR.de • Chart 5 >3rd Japanese-German TBC Workshop • 27. June 2013

Cooling air Hot gas Temperature difference across TBC: ca. 100°C  Increase of lifetime ca. 4 - times

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SLIDE 6

Stress distribution due to thermal gradient

www.DLR.de • Chart 6 >3rd Japanese-German TBC Workshop • 27. June 2013

Biaxial compressive stress Biaxial tensile stress Cooled inner wall Hot outer wall

Cooling air Cooling air Hot gas

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SLIDE 7

Summarizing thermal and mechanical loads

www.DLR.de • Chart 7 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Maximal material temperatures ca. 1000°-1100°C
  • Thermal gradient (temperature drop over a ceramic TBC of 100-200µm

thickness of about 80°-150°C)

  • High thermal heat flux
  • Multiaxial thermally induced stresses
  • High thermal transients (heating and cooling rates)
  • Superposed mechanical loads (centrifugal forces on rotating blades)

Causing

  • Ageing of materials
  • Oxidation of the metallic bond coat
  • Sintering of ceramic top coat
  • Fatigue damages due to cyclic loading (flight cycle)
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SLIDE 8

Investigated coating system

www.DLR.de • Chart 8 >3rd Japanese-German TBC Workshop • 27. June 2013

1 – 10 µm

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SLIDE 9

Laboratory test facility for thermal mechanical loading

www.DLR.de • Chart 9 >3rd Japanese-German TBC Workshop • 27. June 2013

16 Quartz lamps, 1 kW each Internally cooled tensile test specimen Thermal Gradient Mechanical Fatigue = TGMF

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SLIDE 10

View of open furnace

www.DLR.de • Chart 10 >3rd Japanese-German TBC Workshop • 27. June 2013

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SLIDE 11

Time dependent effects

www.DLR.de • Chart 11 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Oxidation of bond coat at high temperature has major impact on

lifetime of ceramic layer

  • It is not practical to perform test cycles with realistic cycle duration

(e.g. 2 - 10 hour flights)

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SLIDE 12

Scheme for accelerated testing

www.DLR.de • Chart 12 >3rd Japanese-German TBC Workshop • 27. June 2013

+

Thermal - mechanical fatigue 500 h 250 h 0 h Time at 1000°C Pre-oxidation until spallation 1000 (50h) 500 (25h) TGMF- cycles

+

Mechanical loads: servo-hydraulic testing machine Thermal gradient over specimen wall by internal cooling

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SLIDE 13

After pre-oxidation: bi-layer thermally grown oxide

www.DLR.de • Chart 13 >3rd Japanese-German TBC Workshop • 27. June 2013

50h/1000°C 200h/1000°C

2 µm

Fine grained intermixed zone Al2O3 +ZrO2 Coarse grained Al2O3

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SLIDE 14

Failure after thermomechanical laboratory testing

www.DLR.de • Chart 14 >3rd Japanese-German TBC Workshop • 27. June 2013

after 933 TGMF*-cycles & 500h pre-oxidation at 1000°C

*TGMF = Thermal Gradient Mechanical Fatigue

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SLIDE 15

After 994 cycles (pre- oxidized 500 h/1000°C)

www.DLR.de • Chart 15 >3rd Japanese-German TBC Workshop • 27. June 2013

A A

‚Smiley-crack‘

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SLIDE 16

3 - dimensional sketch of defects

www.DLR.de • Chart 16 >3rd Japanese-German TBC Workshop • 27. June 2013

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SLIDE 17

Summary of experimental results

www.DLR.de • Chart 17 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Without pre-oxidation no spallation
  • ccurred up to 7000 cycles
  • 250h (500h) pre-oxidation +

1000 cycles, open delamination cracks, spallation

500 h 250 h 0 h Time at 1000°C 1000 (50h) TGMF- cycles

+

Evolution of the ‚smiley‘ cracks is linked to the formation of cracks in the TGO, perpendicular to the applied mechanical load. To form the TGO cracks, axial tensile stresses are necessary. The questions are

  • how can axial tensile stresses evolve in the TGMF tests?
  • why do they only evolve in pre-aged specimens?
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SLIDE 18

Numerical model: Geometry and boundary conditions

www.DLR.de • Chart 18 >3rd Japanese-German TBC Workshop • 27. June 2013

Bi-layered TGO

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SLIDE 19

Numerical model: load cycle

www.DLR.de • Chart 19 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Temperature at the outer

surface is shown

  • Thermal gradient: time

dependent temperature difference between outer and inner wall (not shown)

  • mechanical cycle TGMF

Highest mechanical tensile load, thermal gradient near equilibrium

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SLIDE 20

Axial stresses for elastic – plastic material properties

www.DLR.de • Chart 20 >3rd Japanese-German TBC Workshop • 27. June 2013

Axial stresses across the specimen wall due to

  • thermal gradient
  • mechanical load
  • property mismatch

TGO always under compression even at highest mechanical tensile load Stress free at coating temp. (1000°C, homogenous)

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SLIDE 21

Including time dependent TGO properties: growth strain and creep / relaxation

www.DLR.de • Chart 21 >3rd Japanese-German TBC Workshop • 27. June 2013

Thickening εt and lengthening εl growth strain

εl = 0.1· εt

Karlsson, A.M. and G. Evans,. Acta Materialia, 2001 49(10): p. 1793-1804

Growth strain increases the compressive stress in TGO! Relaxation decreases the compressive stress in TGO!

J.D. French, J.H. Zhao, M.P. Harmer, H.M Chan, G.A. Miller. J. American Ceramic Society 77 (1994)

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SLIDE 22

Effect of relaxation properties on stress accumulation

www.DLR.de • Chart 22 >3rd Japanese-German TBC Workshop • 27. June 2013

Temperature

  • Mech. Load

time Deformation

  • f TGO

Linear-elastic Deformation

  • f TGO

Linear-elastic + TGO-growth

External wall Inner wall

RT 1000°C

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SLIDE 23

Effect of relaxation properties on stress accumulation

www.DLR.de • Chart 23 >3rd Japanese-German TBC Workshop • 27. June 2013

Temperature

  • Mech. Load

time Deformation

  • f TGO

slow relaxation Deformation

  • f TGO

fast relaxation

External wall Inner wall

RT 1000°C

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SLIDE 24

Evolution of axial TGO-stresses

www.DLR.de • Chart 24 >3rd Japanese-German TBC Workshop • 27. June 2013

Aged As Coated

Small grains (d < 1 µm) Fast stress relaxation As Coated TGO Large grains (d >1 µm) Slow stress relaxation Aged TGO

Hypothesis: Initiation of fatigue crack in TGO due to accumulation of tensile stress during subsequent TGMF-cycles

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SLIDE 25

Open questions – things we want to know

www.DLR.de • Chart 25 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Mechanical material properties of the coating materials are still unknown:

Temperature dependent elastic properties, yield strength, creep laws of TGO (intermixed zone and coarse grained layer), bond coat and TBC

  • Most sensitive for damage behavior of the coating system are TGO

properties

  • Measurement of TGO properties is difficult due to small layer thickness

(below 10 µm) and complex chemical composition (intermixed zone)

  • Strategy:
  • measuring the strains in the coating system during TGMF by means of

high energy X-ray diffraction

  • calculating the respective (fitting) material properties by means of finite

element simulation

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SLIDE 26

Experimental set-up at Argonne Advanced Photon source

www.DLR.de • Chart 26 >3rd Japanese-German TBC Workshop • 27. June 2013

  • Argonne National Laboratory,

Argonne, Illinois

  • 1-ID Synchrotron High Energy X-Ray

Beamline; 65 keV Beam Energy

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SLIDE 27

Schematic of test facility configuration

www.DLR.de • Chart 27 >3rd Japanese-German TBC Workshop • 27. June 2013

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SLIDE 28

Top view of heater and beam

www.DLR.de • Chart 28 >3rd Japanese-German TBC Workshop • 27. June 2013

  • 4 Focused IR Lamps
  • 8 kW Total
  • Beam Exit Window
  • 17⁰ 4θ
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SLIDE 29

Measurement method

www.DLR.de • Chart 29 >3rd Japanese-German TBC Workshop • 27. June 2013

TGMF-Parameter:

  • Thermal mechanical cycle

(80min duration)

  • uter surface temperature
  • max. 1000°C, temperature

difference between outer and inner surface ca. 150°C

  • variation of thermal gradient

by variation of cooling flow rate

  • Superposition of mechanical

load cycle Beam parameter:

  • 65 keV beam energy
  • exposure time 0.5 to 15 sec.
  • through specimen center

and grazing

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SLIDE 30

Measurement Methods

www.DLR.de • Chart 30 >3rd Japanese-German TBC Workshop • 27. June 2013

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SLIDE 31

www.DLR.de • Chart 31 >3rd Japanese-German TBC Workshop • 27. June 2013

Qualitative Strain Results

g _ _ p _ g radial bins, covering 350 to 1000 pixels azimuthal bins, covering 0 to 360 deg 560 570 580 590 600 610 620 630 100 200 300 400 500 600 700 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

TGO Al2O3 (116) YSZ ZrO2 (202) Bond Coat AlNi (110)

  • Evaluating radial position of diffraction ring for 0

to 360 degrees azimuthal angle

  • strain is displayed by variation in ring radius
  • significant strain visible in Bond Coat
  • TGO displays texturing

2-D Strained Ring

Azimuthal Angle

0 45 90 135 180 225 270 315 360 0 45 90 135 180 225 270 315 360

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SLIDE 32

Status of the project

www.DLR.de • Chart 32 >3rd Japanese-German TBC Workshop • 27. June 2013

  • TGMF-tests have been successfully performed in-situ at the Advanced

Photon Source at Argonne National Lab

  • Diffraction data acquired for several cyclic loading conditions (up to

1000°C, temperature difference between inner and outer surface up to 150°C, superposed mechanical loads)

  • All phases of the coating system are identified
  • Significant strain observed in bond coat and TGO (qualitatively, calculation
  • f strains and stresses ongoing)
  • TGO and TBC display texture

Acknowledgement

Financial support by National Science Foundation Grants OISE 1157619 and CMMI 1125696, German Science Foundation TRR 103 – A3. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) at Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02- 06CH11357.

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SLIDE 33

www.DLR.de • Chart 33 >3rd Japanese-German TBC Workshop • 27. June 2013

Publications

  • J. Shi, A.M. Karlsson, B. Baufeld, M.Bartsch: Evolution of surface morphology in thermo-mechanically cycled

NiCoCrAlY- bond coats, Mat. Sci. & Eng. A 434 (2006) 39-52

  • M. Bartsch, B. Baufeld, S. Dalkilic, I. Mircea, K. Lambrinou, T. Leist , J. Yan, A.M. Karlsson: Time economic lifetime

assessment for high performance thermal barrier coating systems, Key Eng. Mat., Vol. 33 (2007) 147-154

  • M.Bartsch, B. Baufeld, M. Heinzelmann, A. M. Karlsson, S. Dalkilic, L. Chernova: Multiaxial thermo-mechanical fatigue
  • n material systems for gas turbines, Materialwiss. & Werkstofftechnik 38, (2007) 712-719
  • B. Baufeld, M. Bartsch, M. Heinzelmann: Advanced thermal mechanical fatigue testing of CMSX-4 with oxidation

protection coating, Int. J. fatigue 30 (2008) 219-225

  • M. Bartsch, B. Baufeld, S. Dalkilic, L. Chernova, M. Heinzelmann: Fatigue cracks in a thermal barrier coating system on

a super alloy in multiaxial thermomechanical testing, Int. J. fatigue 30 (2008) 211-218

  • M. Hernandez, A. Karlsson, M. Bartsch: On TGO creep and the initiation of a class of fatigue cracks in thermal barrier

coatings, Surf. Coat. Techn. 203 (2009) 3549-3558

  • M. T. Hernandez, D. Cojocaru, A. M. Karlsson, M. Bartsch: On the crack opening of a characteristic crack due to

thermo-mechanical fatigue testing of thermal barrier coatings, Comp. Mat. Sci. (50) (2011) 2561-2572

  • S. F. Siddiqui, K. Knipe, A. Manero, C. Meid, J. Schneider, J. Okasinski, J. Almer, A.M. Karlsson, M. Bartsch,
  • S. Raghavan: Synchrotron X-Ray Measurement Techniques for Thermal Barrier Coated Cylindrical Samples under

Thermal Gradients, submitted to Review of Scientific Instruments (May 2013)

  • Prof. Dr.-Ing. Marion Bartsch

German Aerospace Center (DLR) Institute of Materials Research Linder Höhe D-51147 Köln Phone: +49-(0)2203-601-2436 e-mail: marion.bartsch@dlr.de

Contact: