I. O. Gilev, A. B. Shubin, P. V. Kotenkov.
ABSTRACT
The thermodynamic properties of aluminum-hafnium melts were studied. The known (ΔfH0298) were analyzed and the unknowns (S0298), (H0298 – H00), Cp(T) и Cp(liq)) thermodynamic properties of congruently melting compounds Al3Hf, Al2Hf, AlHf и Al2Hf3 were calculated. The values of the standard enthalpies of formation for intermetallic compounds were adopted from the literature, where they were calculated using the semiempirical Miedema model, and were equal to -142.4, -134.1, -100.6, -225 kJ/mol for each of the intermetallic compounds, respectively. The analysis and calculations results were used in the thermodynamic modeling (TM) of the Al-Hf melts. The «TERRA» software package was used as a calculation tool for TM. The model of ideal solutions of interaction products (ISIP) was used as a calculation model in the process of modeling the composition and thermodynamic characteristics of melts. This model was used to study the thermodynamics of liquid solutions in the aluminum-hafnium system. The simulation was carried out in an initial argon atmosphere at a total pressure of 105 Pa. The range of temperatures and compositions corresponding to the liquid state of this system 2100-2300K were investigated. A comparison of the results obtained with the results of modeling in the approximation of an ideal solution made it possible to determine the excess integral thermodynamic characteristics (enthalpy, entropy, Gibbs energy) of the Al-Hf melts. It is shown that the absolute value of enthalpies of mixing regularly decreases with increasing the temperature. The found values were compared with the known data on the integral enthalpies of mixing for aluminum melts containing other transition elements of III-IV groups (Sc, Ti, Zr). It was established that the formation of the Al-Hf, Al-Sc, Al-Ti, and Al-Zr liquid alloys is accompanied by a significant heat release. The extreme value of the integral enthalpy of mixing of the Al-Hf alloy is at the same level as the same value for the Al-Ti alloy and does not exceed -32 kJ/mol in modulus. The components of the Al-Sc and Al-Zr systems tend to interact more strongly, ΔHmix reaches a value of -45 kJ/mol. The ISIP model used for TM made it possible to adequately describe the thermodynamic properties of the aluminum-hafnium melt.
KEY WORDS:
thermodynamic modeling, excess thermodynamic functions, melt, aluminum, hafnium, transition metals, associates, intermetallic compounds.
DOI: 10.31857/S0235010621010035