Microstructure and Oxidation Behavior of Atmospheric Plasma-Sprayed Thermal Barrier Coatings

Abstract Thermal barrier coatings (TBCs) are widely used as insulation layered at elevated temperatures in gas turbine components. Yttria-stabilized zirconia (YSZ) ceramic has outstanding properties such as phase stability at high temperature, a prolonged service lifetime, and low thermal conductivity, which make it a promising candidate. The high temperature of gas turbines leads to the transfer of oxygen from the top coat to the bond coat; therefore, oxidation occurs on the bond coat; it is called the thermally grown oxide layer and is mainly considered a failure mechanism of TBC systems. Gas turbine engines that have applications in energy production, transportation, and the defense industry depend on high-temperature TBCs for higher efficiency. During thermal cycling, mechanical forces can occur in turbine engines, oxidation, hot corrosion, the sintering of the top coat, and a thermal expansion coefficient mismatch between the metallic substrate and the ceramic top coat as a result of spallation or crack degradation. TBCs can be affected by coating materials, manufacturing processes, and their microstructure. Spallation of the ceramic top coat is a main problem for TBCs because it leads to oxidation, corrosion, and creeps in the TBC system. This chapter gives brief information about thermal barrier materials and the microstructure and oxidation behavior of TBCs.