FEM simulation of oxidation induced stresses in a simplified thermal barrier coating system

To study the behaviour of the complex failure mechanisms in thermal barrier coatings, a simplified model system is used to reduce the number of system parameters. The artificial system consists of a bond-coat material (fast creeping Fecralloy or slow creeping MA956) as the substrate with a Y2O3 partially stabilized plasma sprayed zircon oxide TBC on top and a TGO between the two layers. A FEM simulation was developed to calculate the stress distribution inside the coating system. The simulation permits the identification of compression and tension areas which are established by the growth of the oxide layer and the stresses which occur during the heating and cooling processes. Full thermal cycles, including heating from RT to 1000°C, dwelling for 2 hours and cooling to RT, were simulated. The stress distributions provide an insight into the possible failure mechanisms in the coating and allow to draw conclusions for optimizing real thermal barrier coating systems. It is shown that the failure mechanism depends on the creep properties of the bond-coat. Therefore, optimizing the creep properties may adjust lifetime of the whole coating system. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)