Determination of the thermodynamic properties of Ni-Ti, Ni-Al, and Ti-Al, and nickel-rich Ni-Al-Ti melts based on the atom and molecule coexistence theory

Abstract

The thermodynamic properties of the full composition range of liquid Ni-Ti, Ni-Al, and Ti-Al alloys were determined using the atom and molecule coexistence theory (AMCT), which is an established thermodynamic model that was used to calculate the mass action concentration (activity) of the structural units in the abovementioned three alloy systems. The temperature dependence of the activity coefficients γiθ of Ti and Al dissolved in molten nickel to form dilute solutions (0 ≤ xi ≤ 0.01) relative to pure liquid were estimated from the calculated activity coefficients of Ti and Al at different temperatures. The standard Gibbs free energy changes ΔsolGm,iθ of dissolving Ti and Al in nickel and the enthalpies of mixing ΔmixHm, i of liquid Ni-Ti, Ni-Al, and Ti-Al were also obtained. The results indicated that the determined thermodynamic properties, such as the ΔsolGm,iθ, and ΔmixHm, i of the liquid binary alloys reasonably agreed with the experimental data previously reported in the literatures. Thermodynamic properties were predicted for three important subsystems, which included the Ni-Ti, Ni-Al, and Ti-Al alloys, and therefore, the activity ai and ΔmixHm, Ni‐Al‐Ti of the nickel-rich liquid Ni-Al-Ti ternary alloys were also obtained at 1873 K. Furthermore, the values calculated using the classical geometric models, including the Toop, Kohler, and Muggianu models, were compared with those determined by the GSM in this study.