Thermophysical property measurements of thermal barrier coatings materials

O. Nashed1, R. Wulf1, O. Fabrichnaya2, G. Savinykh2, M. Kriegel2, H. Seifert2 and U. Gross1

1TU Bergakademie Freiberg, Institute of Thermal Engineering, Germany
2TU Bergakademie Freiberg, Institute of Materials Science, Germany

Keywords: thermal barrier coating
property: thermal diffusivity, thermal conductivity
material: ceramics, insulation materials

Thermal protection systems were the subject of vigorous development over the past few years. Thermal barrier coatings (TBCs) are widely used in advanced gas turbines in order to improve reliability and durability of hot-section metal components as well as the efficiency of engines. The application of TBCs can result in a significant increase of the temperature difference between the hot gas flow and the surface of these components.

To enhance the insulating properties of a thermal barrier coating, one has to focus on new materials with lower intrinsic thermal conductivity than the established yttria-stabilized-zirconia (YSZ, being composed of Y2O3 and ZrO2). Since the fluorites do not offer any other viable candidate material, attention has turned to the pyrochlores (A2 B2 O7, where A and B represent rare earth or transition metal species) as several zirconate pyrochlores have lower thermal conductivities than YSZ. In the present study, zirconates with pyrochlore structure ( La2Zr2O7 , Nd2Zr2O7 , Sm2Zr2O7 ) were investigated having high melting points which is important for thermal barrier coatings at operating temperatures above 1200 C. Samples from the fluorite and the pyrochlore phases in the La2Zr2O7 - Y2O3 system were prepared at 1600 C, and the same has been done for the Nd2Zr2O7 - Y2O3 and Sm2Zr2O7 - Y2O3 systems. Thermophysical properties data of these samples were investigated. Samples were processed at 1600 C, principally by the co-precipitation technique. Other technics, like pulver oxide mixing, were also used. The thermophysical property determination includes Laser-Flash and DSC measurements of thermal diffusivity, heat capacity and phase transformations (using LFA 427 and DSC 404 C Pegasus of NETZSCH, respectively). These data allow evaluation of the thermal conductivity. XRD (X-ray diffraction) and SEM/EDX (Scanning Electron Microscopy combined with Energy Dispersive X-ray) were used for sample characterization.

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