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I.

INTRODUCTION

IN the previous paper, J phase equilibria of the Fe-Ni binary system below 1200 K were analyzed. In this analysis, the two important contributions to the Gibbs energies of the bcc and fcc phases were considered. These contributions are of chemical and magnetic origins. While the magnetic portion of the total Gibbs energy plays an important role in determining the stabilities of phases at low temperatures, its influence on phase stabilities becomes less important at high temperatures. At high temperatures, both the bcc and fcc phases become paramagnetic and the chemical portion of the total Gibbs energy becomes dominant. The values of the solution parameters for the chemical portion of the total Gibbs energies or the nonmagnetic Gibbs energies of the bcc, fcc, and liquid phases may be determined in principle from thermochemical and phase boundary data alone at high temperatures. The high-temperature thermodynamic data of Fe-Ni were reviewed by Hultgren, Desai, Hawkins, Gleiser, and Kelley2 and the phase equilibrium data more recently by Kubaschewski. 3 Subsequent to the review of Hultgren et al.,2 the Gibbs energies of the liquid alloys were redetermined by Mills, Kinashita, and Grieveson, 4 Kubaschewski, Geiger, and Hack, 5 Conard, McAneney, and Sridhar, 6 and Rammensee and Fraser 7 and the enthalpies of mixing by Batalin, Mineko, and Sudavtsova8 and Predel and Mohs 9 by calorimetry. The Gibbs energies of the fcc alloys were redetermined by Kubaschewski et al. ,5 Conard et al. ,6 Rammensee and Fraser, 7 Fleischer and Elliott, ~~ Henriet, Gatellier, and Olette," Ono, Ueda, Yamaguchi, and Moriyama, ~2Dalvi and Sridhar,~3 and Trinel-Dufour and Perrot 14 and the enthalpies of mixing by Spencer, Hayes, and Elford.~5 These thermochemical data and the known phase equilibrium data at high temperatures allow us to fix the values of the solution parameters for the nonmagnetic portions of the total Gibbs energies of the liquid phase, YING-YU CHUANG and KER-CHANG HSIEH, Project Associates, and Y. AUSTIN CHANG, Professor, are with the Department of Metallurgical and Mineral Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706. Manuscript submitted June 24, 1985.

METALLURGICAL TRANSACTIONS A

the fcc phase, and to a lesser extent the bcc phase. The magnetic portions of the total Gibbs energies of the fcc and bcc phases may be determined independent of these data as given in the previous paper. The primary objective of the present study is to analyze all the thermodynamic and phase equilibrium data at high temperatures. This analysis will assure internal consistency among all these data and enables the prediction of metastable solid and liquid equilibria which may be difficult to obtain experimentally. In addition, a knowledge of the type of metastable equilibria is important in the understanding of solidification under nonequilibrium conditions. Furthermore, from this analysis for Fe-Ni and similar analyses for Fe-Cu, 16 Cu-Ni, 17 Fe-S, 18'19 Ni-S, 2~ and Cu-S, 21 thermodynam