Thermodynamic Calculations and Phase Stabilities in the Y-Si-C-O System
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JPEDAV (2007) 28:90–100 DOI: 10.1007/s11669-006-9014-5 1547-7037 ASM International
Thermodynamic Calculations and Phase Stabilities in the Y-Si-C-O System Damian M. Cupid and Hans J. Seifert
(Submitted October 30, 2006) 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.
Keywords
CALPHAD, heat shields, Y-Si-C-O system, yttrium silicate coatings
1. Introduction The Y-Si-C-O system is a key system for the understanding of a manifold of engineering materials composed of SiC and yttrium silicates, respectively. For example, the system is of major interest for the understanding of the liquid phase sintering of SiC ceramics using oxide additives such as Y2O3.[1] In addition, phase reactions in this quaternary system have to be understood to analyze the compatibility and reactions of protective yttrium silicate coatings on carbon fiber reinforced carbon-based composite engineering materials. The yttrium silicate Y2SiO5 was introduced by Ogura et al.[2] as a promising candidate material for the oxidation protection of such materials (e.g., carbon/carbon (C/C), carbon/silicon carbide (C/SiC, C/C-SiC)). For high temperature structural applications, a two-layer coating system consisting of yttrium silicates deposited on a Chemical-Vapor-Deposition-SiC (CVD-SiC) bond coating can be used. This design has the potential for applications as a protective multilayer coating system in gas turbines and reusable space shuttle systems. Various methods such as slip 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. Damian M. Cupid, and Hans J. Seifert, Department of Materials Science and Engineering, University of Florida, Gainesville, FL326116400, USA; Contact e-mail: [email protected]
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casting,[3–5] atmospheric plasma spraying (APS),[2,6,7] low pressure plasma spraying (LPPS),[8,9] and the sol-gel process[10,11]
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