Thermodynamic Properties of Binary Al–Y Melts

The thermodynamic characteristics of aluminum–yttrium melts are studied. An analysis and calculations of the thermodynamic properties ( , , ( ), c p ( T ), and c p (liq)) of the Al 3 Y, Al 2 Y, AlY, Al 2 Y 3 , and AlY 2 compounds are performed. The standard enthalpies of formation of the intermetallics, which are calculated by the semiempirical Miedema model, are –49.4, –60, –63.4, –55, and –46.5 kJ/(mol at), respectively. The calculation results are used for the thermodynamic modeling (TM) of the Al–Y melts, which is performed using the TERRA software as a calculation tool. The modeling of the composition and thermodynamic characteristics of the melts is carried our using the model of ideal solutions of interaction products (ISIP). Based on this model, the thermodynamics of the aluminum–yttrium liquid solutions is studied. The modeling is performed for an initial argon atmosphere at a total pressure of 10 5 Pa. The temperature and composition range corresponding to the liquid state of the system (1900–2100 K) is studied. A comparison of the results obtained and modeling results obtained in the ideal solution approximation allowed us to determine the excess integral thermodynamic characteristics of the melts (enthalpy, entropy, Gibbs energy). The values of enthalpy of mixing are shown to decrease regularly as the temperature increases. The determined values are compared with the available experimental data on the integral enthalpies of mixing of Al–Y melts. The data obtained in the present study by calculation procedures demonstrate a trend toward the strongest interaction of the components over the entire composition range. In this case, the integral enthalpy of mixing reaches –59.6 kJ/mol. The energy curves obtained by TM have an extremum at X Y = 0.46; the composition corresponding to this point is close to that of the AlY intermetallic compound. The experimental data indicate a weaker interaction of the components; the extremum corresponds to –49.6 kJ/mol. The data obtained in the present study agree well with the experimental data; the ISIP model used for TM allowed us to adequately describe the thermodynamic properties of the aluminum–yttrium melt.