Phase equilibria and thermodynamics of binary copper systems with 3d-metals. VII. Concentration-temperature dependences of the thermodynamic functions of mixing for liquid alloys of copper and transition metals

Abstract

The CALPHAD method is used for thermodynamic description of binary copper systems with transition metals based on data on the thermodynamic properties of phases and phase transformations. The parameters of models describing the temperature-concentration dependence of thermodynamic functions of mixing are obtained, and the phase diagrams of the systems are calculated. An analysis of the models makes it possible to establish the behavior of the temperature-concentration dependence of the excess thermodynamic functions of mixing for liquid alloys with different types of interaction of the components and to calculate the excess heat capacity. A correlation between the excess heat capacity of liquid alloys and the mixing enthalpy is established.This paper completes the series of studies on modeling the thermodynamic properties of the phases and phase transformations in binary copper systems with transition metals of the fourth period. In these studies, we used the CALPHAD-method and generalized thermodynamic data on phases and their transformations to give a thermodynamic description of the following systems: Cu-Sc [1], Cu-V [2], Cu-Cr [3], Cu-Mn [4], Cu-Fe [5], Cu-Co [6], and Cu-Ni [7]. In [8], the thermodynamic properties of Cu-Ti melts were described and their metastable transformations were modeled. The results obtained in these studies indicate that the components of these liquid alloys interact in a large variety of ways, which results in complex concentration and temperature dependences of the thermodynamic functions of mixing. The objective of this paper is to generalize and systematize the results obtained in [1-8] and some other publications. CONCENTRATION DEPENDENCE OF THERMODYNAMIC PROPERTIESThe concentration dependence of the excess thermodynamic properties of melts may be analyzed by examining the concentration dependence of their isotherms. It is certainly of interest to correlate the concentration dependence of the excess thermodynamic functions of melts with the behavior of the interacting components in the solid state. To this end, we will simultaneously examine the concentration-dependent isotherms of the thermodynamic functions of melts and the corresponding phase diagrams. Figure 1 compares isotherms of the integral mixing enthalpy of Cu-3d-metal melts with phase diagrams of the following systems: Cu-Sc [1], Cu-Ti [9], Cu-V [2], Cu-Cr [3], Cu-Mn [4], Cu-Fe [5], Cu-Co [6], Cu-Ni [7], and CuZn [9].According to [10,11], the integral mixing enthalpy of liquid copper-scandium alloys achieves a minimum near the equiatomic composition. It is this composition that corresponds to the most thermally stable intermetallic compound (IMC), CuSc, on the phase diagram.Donbass State Mechanical Engineering Academy, Kramatorsk, Ukraine.

Physicochemical phenomena at interfaces

“…The negative deviation of the melts from ideal solutions is also confirmed by thermodynamic studies (low activities of components [15][16][17][18][19][20], negative integral mixing heats, reaching 10.7 ± 3.0 kJ/m 2 for the Ti-Cu system at X Ti = 0.63 and 18.0 ± 2.7 kJ/m 2 for the Zr-Cu system at X Zr = 0.48 [15,21,22]). …”

“…We used the surface tension, molar volumes [7][8][9][10], and thermodynamic activities of components by volume [18][19][20] for the systems studied (Tables 1 and 2). …”

On the abilities and limitations of the linear, exponential and combined models to describe the temperature dependence of the excess Gibbs energy of solutions

“…At medium temperatures (around the liquidus line of any system) the excess heat capacity of mixing has some final value. In all non-ideal liquid alloys for which experimental data exists, it is found that ΔC E p;Φ significantly deviates from zero [19][20][21][22]. It is also shown that its sign is different from the signs of the heat of mixing and the excess entropy of mixing [8,[19][20][21][22] (the latter two quantities usually have the same sign [7,8]).…”