High Temperature Sintering and Oxidation Behavior in Plasma Sprayed TBCs [Single Splat Studies] Paper 2—Relevance of Variation in Materials Systems of TBC Components

摘要

The TBC system’s response to thermal exposure at high temperature is discussed here. The relevance of the microstructural aspects of each component of the TBC system is emphasized. The top coat is a YSZ ceramic coating consisting of a collection of splats on top of one another. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. This study investigates the effect of thermal exposure on the microstructure and sintering behavior in single splats produced using different starting powders since this has been shown to influence the basic microstructure of YSZ topcoat. The bond coat is an MCrAlY metallic coating which serves as an Al reservoir and allows the formation of a protective alumina, Thermally Grown Oxide (TGO) layer between the bond coat (BC) and the top coat (TC) layers. This oxide scale formed upon thermal exposure prevents further oxidation of the underlying component (substrate) and thus provides protection. As such, the content of free Al in the bond coat layer is of significance and makes it crucial to understand the influence of bond coat microstructure evolution and oxidation involved during its formation. The interaction between the bond coat, the TGO and the top coat layers is examined in this study to understand the high temperature behavior of the TBC system with regards to variations in the top coat and bond coat material systems used.