Influence of creep and cyclic oxidation in thermal barrier coatings

The lifetime of thermal barrier coating systems is limited by cracks close to the interfaces, causing delamination. To study the failure mechanisms, a simplified model system is analysed which consists of a bond-coat bulk material, a thermally grown oxide, and an yttria-stabilised zirconia topcoat. The stresses in the model system are calculated using a finite element model which covers the simulation of full thermal cycles, creep in all layers, and the anisotropic oxidation during dwelling. Creep in the oxide and the thermal barrier coating is varied with the use of different creep parameter sets. The influence of creep in the bond-coat is analysed by using two different bond-coat materials: fast creeping Fecralloy and slow creeping oxide dispersion strengthened MA956. It is shown that creep in the bond-coat influences the lifetime of the coatings. Furthermore, a fast creeping thermally grown oxide benefits the lifetime of the coating system.