Tailoring the microstructures of thermal barrier coatings by atmospheric plasma spray

Atmospheric plasma spray (APS) is one of the most important methods to deposit thermal barrier coatings (TBCs). In this chapter, the ceramic topcoats of TBCs with different microstructures and properties deposited by different APS processes are reviewed, including the powder plasma spray and liquid feedstock plasma spray. For TBCs deposited by powder plasma spray process, six kinds of most primary TBCs are focused, including the conventional lamellar TBCs, vertically cracked TBCs, nanostructured TBCs, multilayered TBCs, composite TBCs, and laser-glazed TBCs. For the finely-structured coatings deposited by liquid feedstock plasma spray, columnar-structured TBCs by suspension plasma spray (SPS) and vertically cracked TBCs by solution precursor plasma spray (SPPS) are reported. For each kind of coating, the representative microstructural features, the related process parameters to obtain the microstructure, and the thermomechanical properties and performance of the coating are elaborated. The microstructural change and the related performance degradation of TBCs during thermal exposure are elucidated, followed by an introduction of an effective self-enhanced microstructure design to resist the performance degradation. MCrAlY bond coat deposited by the APS process, as a crucial layer of the TBC system, is also reviewed in aspects of the microstructures, oxidation behaviors, and critical treatments to improve the oxidation resistance.