11. Numerical Simulation of Crack Growth Mechanisms Occurring Near the Bondcoat Surface in Air Plasma Sprayed Thermal Barrier Coatings
- Dongming Zhu,
- Uwe Schulz,
- Andrew Wereszczak and
- Edgar Lara-Curzio
Published Online: 26 MAR 2008
Copyright © 2007 The American Ceramics Society
Advanced Ceramic Coatings and Interfaces: Ceramic Engineering and Science Proceedings, Volume 27, Issue 3
How to Cite
Casu, A., Marqués, J.-L., Vaßen, R. and Stöver, D. (2006) Numerical Simulation of Crack Growth Mechanisms Occurring Near the Bondcoat Surface in Air Plasma Sprayed Thermal Barrier Coatings, 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.ch11
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 2006
Print ISBN: 9780470080535
Online ISBN: 9780470291320
Under thermal cycling, the failure of an air plasma sprayed thermal barrier coating (TBC) on a metallic bondcoat (BC) usually occurs near the interface between both coatings. The local curvature of such an interface is responsible for the stress components which lead to the growth of micro-cracks already produced during the plasma spraying. The growth of oxide scales (TGO) between BC and TBC at high temperatures determines the stress level near the TGO-TBC interface during cooling, where the main stress source is the mismatch in thermal expansion.
A failure mechanism based on finite-element calculations of thermal stress within the TBC is presented, which models the TGO-TBC interface as a sinusoidal profile. Assuming the coating system has completely relaxed its stresses during the thermal cycling hot phase, sub-critical crack growth after cooling to room temperature is calculated for horizontal cracks starting at every hill of the curved TGO-TBC interface profile. Failure is assumed when the growing cracks cover one whole profile wavelength. In a second step, an extension of the presented model is discussed where crack growth follows the path where the energy release rate becomes maximum. Finally, the crack path is implemented directly in the finite-element mesh. The conclusions drawn from the numerical calculations are compared to crack configurations near the TGO-TBC interface, taken from micrographs of thermally cycled samples.