10. Simulation of Stress Development and Crack Formation in APS-TBCS for Cyclic Oxidation Loading and Comparison with Experimental Observations

  1. Dongming Zhu,
  2. Uwe Schulz,
  3. Andrew Wereszczak and
  4. Edgar Lara-Curzio
  1. R. Herzog,
  2. P. Bednarz,
  3. E. Trunova,
  4. V. Shemet,
  5. R. W. Steinbrech,
  6. F. Schubert and
  7. L. Singheiser

Published Online: 26 MAR 2008

DOI: 10.1002/9780470291320.ch10

Advanced Ceramic Coatings and Interfaces: Ceramic Engineering and Science Proceedings, Volume 27, Issue 3

Advanced Ceramic Coatings and Interfaces: Ceramic Engineering and Science Proceedings, Volume 27, Issue 3

How to Cite

Herzog, R., Bednarz, P., Trunova, E., Shemet, V., Steinbrech, R. W., Schubert, F. and Singheiser, L. (2006) Simulation of Stress Development and Crack Formation in APS-TBCS for Cyclic Oxidation Loading and Comparison with Experimental Observations, in Advanced Ceramic Coatings and Interfaces: Ceramic Engineering and Science Proceedings, Volume 27, Issue 3 (eds D. Zhu, U. Schulz, A. Wereszczak and E. Lara-Curzio), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291320.ch10

Author Information

  1. Institute of Materials and Processes in Energy Systems 2, Research Centre Juelich, 52425 Juelich, Germany

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 2006

ISBN Information

Print ISBN: 9780470080535

Online ISBN: 9780470291320

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Keywords:

  • APS-TBCs;
  • TGO;
  • TIT;
  • FEA;
  • TBC

Summary

Oxidation induced spallation of plasma-sprayed thermal barrier coatings (APS-TBCs) is regarded as one major failure mode of ceramic coated gas turbine components. A failure crack path, which is located partly in the thermally grown oxide (TGO) and partly in the TBC is typical for this kind of failure (grey failure). Recent investigations have shown that the related damage evolution starts within the first 10% of life by the formation of micro cracks at the TGO and by opening of pre-existing micro cracks in the TBC. Crack growth and linking of these cracks along the interface lead to final spallation. However, parameters, which govern the kinetics and thus the life-time are not sufficiently known. Finite element simulations of the stress response near the TGO at micrometer scale were conducted corresponding to cyclic furnace tests with identical loading. The load cycle consisted of thermal cycling between 20°C and 1050°C and a dwell-time of 2 h at 1050°C. Continued TGO growth was considered (thickness increase and lateral growth). To include realistic material data, the deformation properties of both the actual NiCoCrAlY bond coat and the plasma-sprayed TBC (ZrO2 with 7–8 wt. % Y2O3) as well as the oxidation kinetics have been experimentally determined and implemented in the FE code. The stress calculations showed two distinct features: (i) a fast development of high tensile stresses in the bond coat with a maximum value directly at the interface bond coat / TGO below a roughness peak, which occurred during the cooling stage and which were maximum at the lowest cycle temperature, and (ii) a development of a lateral region of larger tensile stresses alongside the roughness peak over roughness valleys. The simulation of crack formation at the interface bond coat / TGO using cohesive elements resulted in an early formation of a micro crack at the roughness peak.