Lifetime of Plasma-Sprayed Thermal Barrier Coatings: Comparison of Numerical and Experimental Results

Atmospherically sprayed thermal barrier coatings (TBCs) are nowadays an essential part in modern gas turbines. However, a design integrated use of these coatings is only possible with reliable lifetime models. In this paper, a model is outlined which describes the major failure in TBCs associated with the growth of a thermally grown oxide (TGO) on the bond coat (BC). An essential part of the model is a simplified description of the crack growth as a result of thermal cycling and TGO growth. In addition, the energy release rate for the system is calculated and compared to an estimated critical energy release rate reduced by the crack growth. If both are equal, failure is assumed. The results of the modeling are compared to thermal cycling experiments partly applying a thermal gradient. BC temperatures and also microstructures of the ceramic topcoat have been varied and the influence on the cyclic life studied.