A life time model for ceramic thermal barrier coatings

The life time of Y2O3 stabilized ZrO2 thermal barrier coatings (TBC) has been modelled using a rather simple fracture mechanical approach. The basis of the model, is a finite element analysis of the thermal stresses and approximate assumptions of crack growth along the bond coat (BC)-ceramics interface. The FE calculations show the influence of several microstructural features of the TBC system, as profile of the BC TBC interface, thickness of thermally grown oxide formed during thermal cycling and others, on the stress state. From these results, a specific way of crack growth is predicted and included into the model. The modelling results are compared to life times obtained from thermal cycling experiments. An analysis of the location of failure within the samples, as well as the influence of a variation of the roughness of the BC–ceramics interface on life time are presented. Both are in reasonable agreement with the modelling results. Finally, the shorter life times, which are predicted for samples exposed to an additional compressive mechanical strain, are discussed.