Introduction

TBCs for turbine airfoils in high-performance engines represent an advanced materials technology that has both performance and durability benefits1. As indicated in Figure 1, TBCs are typically composed of a metallic bond coating layer which inhibits oxidation, and an insulative ceramic coating layer.

Foremost of the TBC benefits is the reduction of heat transferred into air-cooled components (Figure 2). Other potential benefits of ceramic coatings include increased resistance to hot corrosion (Figure 3) and oxidation.

TBCs applied by PVD processes are currently tailored to achieve superior strain-tolerant microstructures, which facilitate reliable operation in aircraft engines used for commercial airline and business aircraft missions.

In contrast, the current strain-tolerant microstructure is not optimum for engine environments where significant amounts of sea salt deposition on turbine components can be expected. Consequently,' TBC microstructures are being tailored with densified surface layers in order to achieve lives required for industrial-marine, maritime surveillance, and helicopter applications.

Two PVD processes, sputtering and EB/PVD have been developed to produce ceramic coating systems, with major emphasis on stabilized (yttria and ceria) zirconia. At this time, sputtering remains a laboratory process. In contrast, EB/PVD ceramic coatings can be applied at commercially viable rates and production is imminent.2

1T.E. Strangman, "Thermal Barrier Coatings for Turbine Airfoils," Thin Solid Films, 127 (1985), 93-105. 2R. Shankar, "Electron-Beam Physical Vapor Deposition Development of Zirconia Coatings," Presented at Coatings for Advanced Heat Engines Workshop, Castine, Maine, 1987.

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