Thermophysical properties of thermal barrier coatings

Thin layers of thermal barrier coating (TBCs) are applied to metallic components of heat engines to reduce metal temperatures and to provide environmental protection. This results in increased engine efficiency and prolonged operational life. Of special current interest is the use of TBCs in aircraft engines. The TBCs, often yttria-stabilized zirconia (YSZ), are deposited on nickel or cobalt-based superalloy components used in high-temperature environments. The thermophysical properties (especially thermal conductivity) of the coatings are extremely important since, together with the coating thickness, they control the temperature drop across the coating. Accurate determinations of the thermal conductivity of the coating are critical in designing the engines and in research aimed at decreasing the thermal conductivity of TBCs. Such research includes very thin multiple layers, compositional changes and deposition techniques. The number of potentially applicable techniques is limited because of the sample configurations. Consequently, the reproducibility of results from a technique or agreement between the results from different techniques may not be satisfactory. © 1999 Elsevier Science S.A. All rights reserved.