Thermodynamics of formation of Y-Ni alloys
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INTRODUCTION
THEthermodynamics of formation of intermediate phases in the Y-Fe and Y-Co binary systems has already been measured.~'2 The present investigation completes the study of the binary systems of yttrium with the first group VIII transition metals; specifically, the present work deals with the thermodynamics of phase formation for all intermediate phases in the Y-Ni system. This series of studies was undertaken at the suggestion of Watson and Bennett 3 who have developed a simplified band theory approach for the estimation of the heats of formation of binary transition metal-transition metal alloys. It was their belief that thermodynamic data for the Y-Fe, Y-Co, and Y-Ni systems would provide a useful test of their approach. Phase relationships in the Y-Ni system were first investigated by Beaudry and Daane 4 and later by Domagala et al. 5 In the region 25 to 100 at. pct Y, the two investigations agree as to the occurrence of phases with stoichiometries of YNi4, YNi3, YNi2, YNi, Y3Ni2, and Y3Ni. The two investigations differ with regard to the stoichiometry of the most Ni-rich intermediate phase with Beaudry and Daane4 reporting Y2Ni~7 and Domagala et al. 5 reporting YNi9. A subsequent crystallographic study6 indicates that the most Ni-rich phase has, indeed, an ideal stoichiometry of Y2Ni17 and not YNig. An additional difference between the two investigations is that Beaudry and Daane 4 reported a phase at Y2Ni7 between YNi4 and YNi3 whereas Domagala et al. 5 omit such a phase. Because the alloying behavior of Y is normally analogous to that of the heavier rare earths and because Buschow's 7 survey of the phases in the R-Ni systems (R = rare earth) indicates that an R2Ni7 phase occurs in all of the heavier R-Ni systems, the occurrence of such a phase in the Y-Ni system is consistent with the general trend.
P R. SUBRAMANIAN, formerly Graduate Assistant, Department of Materials Science and Engmeenng, Iowa State University, is now Research Associate, Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon Umversity, Schenley Park, Pittsburgh, PA 15213 J.F. SMITH is Professor, Department of Materials Science and Engineerrag, and Senior Metallurgist, Ames Laboratory, Iowa State Umverslty, Ames, IA 50011. Manuscript submitted December 10, 1984.
METALLURGICALTRANSACTIONS B
Lemaire and Paccard 8 have discussed the crystallographic relationships among the Ni-rich phases in the system and have shown that they are all related to the YNi5 structure. A synopsis of crystallographic data for the various Y-Ni phases is shown in Table I, and Figure 1 shows a composite phase diagram which was taken from Elliott's compilation. 9 No experimental data were found which pertain to the thermodynamics of the Y-Ni system although van Mal et al. 1o have estimated the enthalpy of formation of various Y-Ni intermediate phases on the basis of the Miedema model.l~ Their prediction for the enthalpy of formation of a solid equiatomic alloy differs from the prediction of the Watson and Bennett model ~2by almo
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