Thermophysical characterization of thermal barrier layers

Increasing the efficiency of modern gas turbines requires the increase of operating temperature. Current fuel gas temperatures above 1400 degrees C significantly exceed critical temperatures of the turbine steels used. To ensure operational safety, the turbine blades are actively cooled and also protected by protective layers, the so-called thermal barrier coatings (TBC). Since the TBC are ceramic layers, an adhesion promoter (bond coat) must be applied to increase the adhesive strength. Since properties of thin layers can differ from properties of the bulk material and are also influenced by the manufacturing method, an investigation of the thermal and infrared-optical properties of the actual layer is essential, especially in the high temperature range. For this purpose, samples of the pure carrier steel, the carrier steel with bond coat and the complete layer system of carrier steel, bond coat and TBC of various thicknesses were produced and examined using the laser flash method. The evaluation was carried out analytically, starting from the single-layer sample, via the two-layer and three-layer systems. These investigations were completed by infrared-optical characterizations, allowing the description of the heat transport through the layer systems. These measurements allow a future quantification of the individual heat transport mechanisms occurring in ceramics.