June 22-27, 2014
A thermodynamic database has been developed for calculating thermochemical interaction of thermal barrier coatings, namely 7YSZ (yttria partially stabilized zirconia), with CaO-MgO-Al2O3-SiO2 (CMAS) deposits. CaO-MgO-Al2O3-SiO2-Y2O3-ZrO2 is thus the core system for understanding and modeling of processes occurring between CMAS and TBC. A good thermodynamic description of all phases in the system is essential in modeling related to materials design and process optimization. An efficient technique used to obtain a self-consistent thermodynamic database is called the CALPHAD method , where the Gibbs energy of each phase is described with a mathematical model. The Gibbs energy of the total system is then minimized with respect to temperature and composition in order to predict the most stable phases under equilibrium conditions. In this work Y2O3-ZrO2 was incorporated into an existing description  of the CaO-MgO-Al2O3-SiO2 system. Many pseudo-binaries and ternaries are assessed within the CaO-MgO-Al2O3-SiO2-Y2O3-ZrO2 system. Two examples on calculated phase diagrams are shown below. The compound energy formalism  is used to model solid oxide solutions such as spinels, monoxide, corundum, zirconia, yttria etc. The ionic two-sublattice liquid model [4,5] is used to model molten slags.
Lina Kjellqvist, Johan Brattberg, Ake Jansson, and Huahai Mao, "A thermodynamic database for simulation of CMAS and TBC interactions" in "Thermal Barrier Coatings IV", U. Schulz, German Aerospace Center; M. Maloney, Pratt & Whitney; R. Darolia, GE Aviation (retired) Eds, ECI Symposium Series, (2015). http://dc.engconfintl.org/thermal_barrier_iv/25