1. The Effect of Elastic Compliance of PYSZ EB-PVD Thermal Barrier Coatings on Cyclic Test Lives
Byron Williams – BAE Systems
David. S. Rickerby – Rolls-Royce Surface Engineering
Robert E. Jones – Rolls-Royce Surface Engineering
December 2005
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2. Background (i)
Turbine Surface Technologies Ltd manufacture thermal barrier coatings (TBC) for Rolls-Royce
Process steps involve;
Production of Ni based super alloy turbine blades at Rolls-Royce
Platinum coat applied by electroplating
Heated to produce Ni-Pt-Al alloy bond coat
December 2005
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3. SEM image showing cross-section through bond coat
December 2005
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4. Background (i)
Turbine Surface Technologies Ltd manufacture thermal barrier coatings (TBC) for Rolls-Royce
Process steps involve;
Production of Ni based super alloy turbine blades at Rolls-Royce
Platinum coat applied by electroplating
Heated to produce Ni-Pt-Al alloy bond coat
PYSZ TBC deposited by electron beam vapour deposition
December 2005
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5. SEM Image showing columnar microstructure of PYSZ TBC Coating
December 2005
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6. Background (i)
Turbine Surface Technologies Ltd manufacture thermal barrier coatings (TBC) for Rolls-Royce
Process steps involve;
Production of Ni based super alloy turbine blades at Rolls-Royce
Platinum coat applied by electroplating
Heated to produce Ni-Pt-Al alloy bond coat
Y-Zr TBC deposited by electron beam plasma
One blade from every batch (~30) sectioned for microscopy, chemical analysis and cyclic testing
December 2005
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7. Background (ii)
Cyclic testing of blade sections gives very variable results
December 2005
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8. Variability of cyclic test data for standard production blades
Data for average minimum cyclic life – error bars = +/- 1 standard deviation
December 2005
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9. Analysis of residual stress in TBC
Background (ii)
Cyclic testing of blade sections gives very variable results
Work program initiated to elucidate factors giving rise to variability which was structured as;
Detailed study of bond coat chemistry
Characterisation of thermally grown oxide (Al2O3)
Analysis of residual stress in TBC
December 2005
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10. asubstrate > apYSZ > aTGO
Background (iii)
EB-vapour deposition process carried out at ~ 1100oC
Coefficient of thermal expansion
asubstrate > apYSZ > aTGO
On cooling the blade to RT the thermal mismatch generates residual stress in TBC coating
Can this be measured – or inferred?
Does this vary from sample to sample?
Measure the cross-sectional hardness’ of representative samples
December 2005
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11. TBC Characterisation
Microindentation (Vickers Hardness – Buehler Micromet indentation tester)
Indenting at 30 points along centre of TBC CX & CC
(Analogous procedure used for nanoindentation)
Convex
Concave
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12. Vickers Hardness Testing
Indenting at 30 points along middle of TBC coating
Position of indents
50mm
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13. Typical Microindentation Results
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14. Microindentation Results: Summary
Hardness data very scattered.
Mean hardness for concave surface always greater than convex ~5GPa cx, ~6.2 GPa cc.
Sample to sample variation within analysed population.
Good cyclic life – narrower distribution
Poor cyclic life – harder regions in coating
Mean hardness does not vary markedly across population but sample-to-sample hardness distributions show marked variability
December 2005
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15. Correlation with Cyclic Life Data
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16. Correlation with Cyclic Life Data
December 2005
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17. Weibull plot of all TBC Hardness Data
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18. Correlation Results
No trend apparent for convex surface, but concave data shows weak trend of increasing lifetime correlating with lower hardness
Data sufficiently encouraging to justify further study – use nanoindentation to investigate variability in modulus
December 2005
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19. Nanoindentation Samples analysed at Cranfield University
Analysed at 50 mN & 200mN / Triangular diamond indenter
Two samples evaluated based on extremes from correlation data
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20. Nanoindentation sample selection
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21. Nanoindentation Samples analysed at Cranfield University
Analysed at 50 mN & 200mN / Triangular diamond indenter
Two samples evaluated based on extremes from correlation data
Literature data used to calculate Modulus
Weibull statistics used to present distribution
December 2005
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22. Nanoindentation: Data Treatment (i)
Poisson ratio for PSYZ taken from Rolls-Royce data base – 0.15
Literature data used for Poisson ratio and hardness for diamond;
Hardness = 1141GPa
Poisson’s ratio = 0.07
Thus obtain value for modulus from nanoindentation data using the following
December 2005
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23. Nanoindentation: Data Treatment (ii)
Nanoindentation analysis returns a value for the reduced modulus viz,
Rearranging and substituting values;
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24. Nanoindentation Data (i) – Convex surfaces
E values,
50mN load.
December 2005
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25. Nanoindentation Data (ii) – Concave Surfaces
E values,
50mN load.
December 2005
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26. Nanoindentation Data (iii) – Convex Surfaces (again)
Data for modulus, E.
200mN load.
December 2005
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27. Nanoindentation Data (iv) – Concave Surfaces (again)
Data for modulus, E.
Note b values & high end data for
200mN load.
December 2005
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28. Nanoindentation 50 vs 200mN
Marked change in response going from 50 to 200 mN indentation load
Distribution in modulus data larger for lower load (CX & CC)
Lower indentation loading, obtain material (i.e. column) properties
Higher indentation loading – interrogating coating properties
December 2005
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29. Conclusions
Microindentation testing of TBC’s shows variability in sample-to-sample hardness
Correlation of hardness data with cyclic test data suggests trend of high measured hardness values correlating with low cyclic test life
Nanoindentation analysis of samples showing large differences in cyclic test life shows marked differences in modulus
Poor performing sample more rigid cf sample showing increased test life
Data suggest variation in mechanical properties contributes significantly to variability observed for cyclic test performance
December 2005
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30. Acknowledgements
Andy Payne, Prof. John Nicholls – Cranfield University
Paul Morrell – Rolls-Royce Surface Engineering
BAE Systems / Rolls-Royce
December 2005
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