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
Outline
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• 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
Turbine blades in an aircraft engine
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Rotating turbine blades
Engine Alliance GP7000
Load and temperature cycle of a flight mission
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Turb
ine
entra
nce
tem
pera
ture
(TE
T)
time (min) 0 1
201
200 20
Rot
atio
nal s
peed
(rpm
)
Taxi Taxi
Take-off Climb
Cruise
Approach
Thrust-reverse
→ very high heating and cooling rates during take off and after landing
Turbine blades with protective coatings
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Cooling air
Hot gas
Temperature difference across TBC: ca. 100°C Increase of lifetime ca. 4 - times
Stress distribution due to thermal gradient
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Biaxial compressive
stress Biaxial tensile stress
Cooled inner wall Hot outer wall
Cooling air Cooling air
Hot gas
Summarizing thermal and mechanical loads
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• 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)
Investigated coating system
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1 – 10 µm
Laboratory test facility for thermal mechanical loading
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16 Quartz lamps, 1 kW each
Internally cooled tensile test specimen
Thermal Gradient Mechanical Fatigue = TGMF
View of open furnace
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Time dependent effects
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• 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)
Scheme for accelerated testing
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+
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
After pre-oxidation: bi-layer thermally grown oxide
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50h/1000°C 200h/1000°C
2 µm
Fine grained intermixed zone Al2O3 +ZrO2
Coarse grained Al2O3
Failure after thermomechanical laboratory testing
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after 933 TGMF*-cycles & 500h pre-oxidation at 1000°C
*TGMF = Thermal Gradient Mechanical Fatigue
After 994 cycles (pre- oxidized 500 h/1000°C)
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A A
‚Smiley-crack‘
3 - dimensional sketch of defects
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Summary of experimental results
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• Without pre-oxidation no spallation occurred 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?
Numerical model: Geometry and boundary conditions
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Bi-layered TGO
Numerical model: load cycle
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• 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
Axial stresses for elastic – plastic material properties
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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)
Including time dependent TGO properties: growth strain and creep / relaxation
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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)
Effect of relaxation properties on stress accumulation
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Temperature Mech. Load
time
Deformation of TGO Linear-elastic Deformation of TGO
Linear-elastic + TGO-growth
External wall
Inner wall
RT
1000°C
Effect of relaxation properties on stress accumulation
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Temperature Mech. Load
time
Deformation of TGO slow
relaxation
Deformation of TGO fast
relaxation
External wall
Inner wall
RT
1000°C
Evolution of axial TGO-stresses
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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
Open questions – things we want to know
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• 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
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
Schematic of test facility configuration
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Top view of heater and beam
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• 4 Focused IR Lamps • 8 kW Total
• Beam Exit Window
• 17⁰ 4θ
Measurement method
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TGMF-Parameter: • Thermal mechanical cycle
(80min duration) • outer 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
Measurement Methods
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Qualitative Strain Results g _ _ p _ g
radial bins, covering 350 to 1000 pixels
azim
utha
l bin
s, c
over
ing
0 to
360
deg
560 570 580 590 600 610 620 630
100
200
300
400
500
600
7000
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
1
35
180
225
27
0 3
15
360
0
45
90
1
35
180
225
27
0 3
15
360
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 of 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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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 on 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: [email protected]
Contact: