Enthalpies of formation of liquid binary (copper + iron, cobalt, and nickel) alloys
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I.
INTRODUCTION
THERMODYNAMIC properties of formation of liquid copper alloys with the metals of iron subgroup (Fe, Co, Ni) were measured or estimated a number of times in the past by various teams of researchers.[1–43] The interest shown in thermodynamics of these systems is not surprising, considering the very common metals involved as the constituents. At the same time, despite the variety of data reported, some of them are contradictory, while the others disagree with respect to the concentration dependence and/or absolute values of the apices of mixing enthalpies. We have found certain remaining ambiguities in the thermochemistry of alloying of copper with Group VIII metals unacceptable, and decided to repeat the direct calorimetric determination of mixing enthalpies in two of these systems (Cu-Fe, Cu-Ni) in a consistent way (enthalpies of formation of liquid CuCo alloys have been measured by us previously[21]). This was particularly important in the light of systematic revision of the thermodynamic properties of liquid binary copper alloys with transition metals of the fourth period carried out by us since 1992.[44,45,46] Among the other goals of such revision was a need for a reliable experimental database to compare with the results of first principles quantum-mechanical calculations conducted at present by one of us (IVN). Phase diagrams of all three systems, redrawn by Massalski,[47] are known quite well. No compounds are reported in either of them. While diagrams for Cu-Fe and Cu-Co systems look much alike, there is a marked difference in I.V. NIKOLAENKO, Associate Professor, is with the Department of Chemistry, National University of Lesotho, Lesotho, Southern Africa. M.A. TURCHANIN, Associate Professor, is with the Department of Technology and Apparatuses of Cast Manufacture, Donbass State Mechanical Engineering Academy, 343913 Kramatorsk, Ukraine. Manuscript submitted February 13, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
the appearance of the Cu-Ni system. Both the Cu-Fe and Cu-Co systems have peritectic-type diagrams with limited solid solubility of components in each other. Solubility of copper in (gFe) and (aCo) is characterized by a remarkably retrograde solidus with maximum values xCu 5 0.12 at 1683 K in (gFe) and xCu 5 0.197 at 1640 K in (aCo). Maximum solubility of the preceding metals in fcc Cu-rich solid solution (ε phase) is xFe 5 0.046 at 1369 K and xCo 5 0.08 at 1385 K, respectively. Two peritectic reactions, (dFe) 1 L ↔ (gFe) at 1758 K, (gFe) 1 L ↔ (Cu) at 1369 K, and one eutectoid reaction, (gFe) ↔ (aFe) 1 (Cu) at 1123 K, are reported for the Cu-Fe system. A similar peritectic reaction, (aCo) 1 L ↔ (Cu) at 1385 K, is observed in the Cu-Co system. Both systems have a noteworthy extended flat liquidus, slightly more pronounced for Cu-Fe (approximately in the range 0.2 , xFe , 0.8 at about 1723 K, compared to 0.25 , xFe , 0.75 at about 1673 K for the Cu-Co system), and are characterized by a trend toward liquid state immiscibility. In particular, miscibility gap was observed for
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