Thermodynamic Calculation of Phase Equilibria in the Ti–Co and Ni–Sn Systems

Abstract

A thermodynamic model for the titanium-cobalt system has been developed utilizing measured enthalpies of mixing of the liquid and evaluated phase-diagram data. The free energies of the liquid, bcc, fcc, and hcp solid solutions, and TiCo, Ti2Co, TiCo2, and TiCo3 compounds were calculated for a temperature of 400 K. The model and measured heats of crystallization have been used to predict the free energy of the metastable amorphous phase at 400 K, needed for comparison with experimental results on the mechanical alloying of Ti and Co. The predicted glass-forming range for alloys prepared by mechanical alloying is from 10 to 81.5 at. % Co. We adopted a similar approach for modeling the Ni–Sn system to calculate the free energies of Ni3Sn, and Ni3Sn2, and the liquid (amorphous) and fcc solid solutions in the nickel-rich region at 240 K. In this system the inclusion of the magnetic contribution to the free energy of the Ni-rich fcc solid solution is important in interpreting the results of mechanical alloying. We propose a simple transformation of the free-energy curves, which assists in the graphical identification of the glass-forming ranges.