Aspects of the morphological evolution in thermal barrier coatings and the intrinsic thermal mismatch therein

The evolution of interfacial deformations and stresses in thermal barrier coatings due to the formation of the thermally grown oxide and the intrinsic thermal mismatch is investigated. The study focuses on systems that are prone to displacement instabilities of the thermally grown oxide and numerical models spanning a range of properties are investigated. Material changes in the Pt-modified aluminide bond-coat, such as martensitic transformation and the change from β- to γ′-grains, are considered. The numerical simulations show that when the mismatch is large enough to cause overall yielding in the bond-coat, the thermal expansion of the substrate (the superalloy) will rule the system response. Furthermore, the results suggest that the stresses and the interfacial deformation-thus the coating's lifetime-may be optimized if the martensitic transition temperature can be controlled for bond-coats undergoing such transformations. However, we show that due to the sensitivity of the system, this is unlikely to be successful for a real material system.