Thermal barrier coatings on surfaces with micro-machined roughness profiles

Thermal barrier coating systems are used to enhance the temperature resistance of hot section components in gas turbines. The coatings protect the underlying nickel based components and consist of the bond coat (BC) the thermal barrier coating (TBC) and a thermally grown oxide (TGO) between the BC and TBC. The coating systems fail in service at or near the TBC/TGO interface. To study the failure mechanisms a simplified coating system is introduced which consists of a MCrAlY bond-coat material as the substrate, a TGO, and ayttria-stabilised zirconia TBC as a topcoat. The TBC is applied by atmospheric plasma spraying on top of specimens with defined roughness profiles, manufactured by a micromachining process. The main advantage of micro-machining is a defined interfacial roughness between the TBC and the BC in contrast to sandblasted specimens. Furthermore, a FEM simulation of the coating system was developed which approximates the interface by sinusoidal functions. This simplified model system and additional FEM calculations show the influence of varying the interfacial roughness between the BC and the TBC.