Thermodynamic Calculations and Phase Stabilities in the Y-Si-C-O System

A thermodynamic computer dataset for the Y-Si-C-O system was used for calculations of multicomponent, multiphase reactions. The phase reactions of yttrium silicate coatings for the oxidation protection of C/SiC-based composites were analyzed. They were simulated as a function of the temperature and other environmental conditions. To illustrate the high temperature behavior of the coatings, isothermal sections, isopleths, pseudo-binary and -ternary diagrams, phase fraction diagrams, volatility diagrams and potential phase diagrams are presented. Additionally to the thermodynamic aspects, mass balance criteria were taken into account for the analysis of the active/passive oxidation in the coating system. This article was presented at the MultiComponent Alloy Thermodynamics Symposium sponsored by the Alloy Phase Committee of the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12–16, 2006, to honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI, Patrice Turchi of the Lawrence Livermore National Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany.