Modeling of thermal and lattice misfit stresses within a thermal barrier coating

An analytical model was developed to determine the stress distribution over thickness for a multilayered thermal barrier coating (TBC) system deposited within a cylindrical reaction vessel. Temperature dependent material properties were used to estimate the stress values. It was found that, even for small lattice misfits, very high compressive elastic stresses could exist at the ceramic-bond coat interface immediately after deposition. Furthermore, this interfacial stress could ultimately relax to a lower value with increasing film thickness by dislocation nucleation. In the presence of a Thermally Grown Oxide (TGO), however, a tensile stress was generated within the oxide layer and discrete changes in stress profile were predicted at ceramic-TGO and TGO-bond coat interfaces. While the stress-change was higher at the ceramic-TGO interface for a high deposition temperature, the change was greater at the TGO-bond coat interface at a lower deposition temperature. A high compressive stress was predicted within the TGO layer upon cooling down the TBC system to room temperature and the stress-change was highest at the TGO-bond coat interface. Finally, when the TGO layer was subjected to fatigue loading under compressive mean stress during thermal cycling, the model predicted that the internal pressure of the cylindrical vessel reduces the magnitude of mean stress and increases the stress-range in the thermal stress cycle. The effects of evolved stresses on the context of interfacial failure of TBCs should provide fundamental insight into material selection and component design.