Experimental and computational phase studies of the ZrO2-based systems for thermal barrier coatings

Abstract

The ZrO2-based materials are practically important as the thermal barrier coatings (TBC) for high temperature gas turbines, due to their low thermal conductivity, high temperature thermal stability and excellent interfacial compatibility. Studies of the phase equilibira, phase transformation, and thermodynamics of the ZrO2-based systems can provide the necessary basic knowledge to develop the next generation TBC materials. In the thesis, the systems ZrO2 - HfO2, ZrO2 - LaO1.5, ZrO2 - NdO1.5, ZrO2 - SmO1.5, ZrO2 - GdO1.5, ZrO2 - DyO1.5, ZrO2 - YbO1.5 and ZrO2 - GdO1.5 - YO1.5 were experimentally studied. The samples were prepared by the chemical co-precipitation method, with aqueous solutions Zr(CH3COO)4, HfO(NO3)2, and RE(NO3)3×xH2O (RE=La, Nd, Sm, Gd, Dy, Yb) as starting materials. Various experimental techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), differential thermal analysis (DTA), and high temperature calorimetry were employed to study the phase transformation, phase equilibria between 1400 and 1700°C, heat content and heat capacity of the materials. A lot of contradictions in the literature were resolved and the phase diagrams were reconstructed.

ZrO2-basierte Materialien sind wegen ihrer niedrigen Waermeleitfaehigkeit, ihrer hohen Hochtemperaturbestaendigkeit und ausgezeichneten Grenzflaechenkompatibilitaet als Waermedaemmschichten (WDS) fuer Hochtemperaturgasturbinen praktisch wichtig. Forschungen an Phasengleichgewichten, Phasenumwandlungen und der Thermodynamik von ZrO2-basierten Systemen koennen die notwendigen grundlegenden Kenntnisse zur Verfuegung stellen, um die naechste Generation von WDS Materialien zu entwickeln. In dieser Dissertation werden die Systeme ZrO2 - HfO2, Zr - O, Hf - O, ZrO2 - LaO1.5, ZrO2 - NdO1.5, ZrO2 - SmO1.5, ZrO2 - GdO1.5, ZrO2 - DyO1.5, ZrO2 - YbO1.5 und ZrO2 - GdO1.5 - YO1.5 experimentell und rechnerisch untersucht.