Phase relations in the ZrO2-La2O3-Y2O3-Al2O3 system
Final Report Abstract
2.1 . Allgemeinverständliche Darstellung der wesentlichen Ergebnisse und der erzielten Fortschritte gegenüber dem Stand des Wissens zum Zeitpunkt der Antragstellung The thermodynamic description of quaternary system ZrO2-La2O3-Y2O3-Al2C>3 was not available so far. There were assessments of thermodynamic parameters for binary systems produced by Calphad method. However most of them needed to be re-assessed because of incompatibility of models used for different systems and appearance of new experimental data. The only ternary system description was available for the ZrO2-Y2C>3-Al2O3 system [1]. In the present investigation, the binary descriptions have been derived based on recent experimental data. The same models - compound energy formalism for solid phases and partially ionic two-sublattice model for liquid have been used for all binary systems. Thermodynamic parameters for the ZrO2-La2U3 system have been assessed in this study with special attention to triangulation in the ternary system of ZrOi-LazOj-AhOs. It has been demonstrated that the phase equilibria between solid phases in the ternary ZrC>2-La2O3-Al2O3 system constrain thermodynamic parameters in the binary ZrO2-La2U3 system. The ternary interaction parameter has been assessed for the liquid phase using experimental data on liquidus surface [2], Isothermal sections at 1523, 1923 K, liquidus surface and several vertical sections have been calculated and compared with available experimental data. The revealed several inconsistencies between calculations and experimental data are due to the fact that calculations gave wider field of primary crystallisation of pyrochlore phase than indicated by [2]. The SEM investigation of melted samples performed in this work has confirmed the calculated primary crystallisation field of pyrochlore. The thermodynamic databases for the ZrO2-La2O3-Y2O3 and La2O3-Y2O3-Al2O3 ternary systems have been derived by combining of binary descriptions. The isothermal sections and liquidus surfaces have been calculated for both systems. The experimental data for these systems are very scarce and uncertain. The obtained results could be used for planning of new experiments. The derived thermodynamic descriptions for ternary systems are combined and thermodynamic dataset for the quaternary ZrCVI^C^^Os-AkCh system has been obtained. 2.2. Ausblick auf künftige Arbeiten und Beschreibung möglicher Anwendungen Further experimental phase studies should be performed in the ZrO2-La2O3-Y2O3 and La2O3-Y2C>3-Al2O3 systems. The preliminary calculations based on extrapolations from binary systems into ternaries can be used for selection of compositions to be investigated. The obtained thermodynamic description of the ZrO2-La2O3-Y2O3-Al2C>3 system could be applied to calculate equilibrium phase diagrams important for understanding interactions between layers in thermal barrier coating (TBC) systems. In addition, the calculations of temperatures of diffusionless transformations are possible to understand the effect of doping on TBC stability and durability.
Publications
- O. Fabrichnaya, Ch. Wang, M. Zinkevich, F. Aldinger: "Thermodynamic modelling in the ZrO2-La2O3-Al2U3 and ZrO2-La2O3-Y2C>3 systems" in E-MRS (Fall meeting of European Materials Research Society" 4-8 Sept. 2006, Warsaw, Poland, p. 192.
