ICF13B

13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Thermomechanical fatigue life of a TBC – comparison of computed and measured behaviour of delamination cracks Sören Sjöström1,*, Håkan Brodin1,2, Magnus Jinnestrand1 1 Department of Management and Engineering, Linköping University, SE-58183 Linköping, Sweden 2 Siemens Industrial Turbomachinery AB, SE-61283 Finspång, Sweden * Corresponding author: email@address.aa.b.cc Abstract Abstract Thermal barrier coatings (TBCs) are used in hot parts of gas-turbine engines in order to increase gas temperatures and improve thermal efficiency. A TBC consists of a metallic bond coat (BC) and a ceramic top coat (TC). During high-temperature service, thermally grown oxide will form in the BC/TC interface. This together with the general difference in mechanical and thermal expansion properties leads to a tendency of spalling damage, by which areas of the coating will flake off during thermomechanical cycling. The modelling of this damage process is rather difficult, but the authors have managed to set up a fracture-mechanically based model, which takes thermal cycling, mechanical cycling and oxide growth into account. The model has been tested and verified under controlled laboratory conditions, using thermal cycling furnaces and continuous inspection of damage development. It has also been used in an FEM computation environment for prediction of TBC spalling in real gas-turbine components. In this article, the model is described, computations are shown of the development of a typical delamination crack in the BC/TC interface, and the computed results are compared with actual delamination crack behaviour seen in the corresponding testing. Keywords TBC, fracture-mechanical model, experimental, FEM, interface crack 1. Introduction A thermal barrier coating (TBC) is a ceramic coating applied for thermal insulation purposes on a metallic substrate. Figure 1. Schematic figure of a TBC-coated gas-turbine blade. Typical spalling mechanisms marked are explained below Fig. 1 shows a schematic example of a TBC-coated gas-turbine blade. The TBC consists of a substrate (light grey in Fig. 1) on which a metallic bond coat (darker grey in Fig. 1) is applied. On top of the bond coat, finally, the top coat ceramic (yellow in Fig. 1) is applied. The substrate is usually a nickel-based superalloy, the bond coat is an alloy, rich in Al, and the top coat ceramic is usually

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