A parametric study of the stress state of thermal barrier coatings Part II: cooling stresses

The development of cooling stresses in the thermal barrier coating (TBC)/thermally grown oxide (TGO)/bond coat interface region is calculated for a TBC coated superalloy specimen using a finite element model. Stresses in the system are determined by the thermal mismatch between the components, with the TGO and the bond coat having an opposing effect on the TBC stresses. It is shown that TGO induced stresses dominate even at a moderate TGO layer thickness. Creep processes strongly influence the cooling stresses, and fast creep in TBC and bond coat significantly reduces TBC stresses, possibly leading to a substantial increase in TBC lifetime. The influence of the interface geometry and of bond coat plasticity on the cooling stresses are also studied.