Thermodynamic calculation of phase equilibria in the Ti-Co and Ni-Sn systems

A thermodynamic model for the titanium-cobalt system has been developed uti lizing measured enthalpies of mixing of the liquid and evaluated phase-diag ram data. The free energies of the liquid, bcc, fee, and hcp solid solution s, and TiCo, Ti2Co, TiCo2, and TiCo3 compounds were calculated for a temper ature of 400 K. The model and measured heats of crystallization have been u sed 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 mech anical 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 fee solid solutions in the nickel-ri ch region at 240 K. In this system the inclusion of the magnetic contributi on to the free energy of the Ni-rich fee solid solution is important in int erpreting the results of mechanical alloying. We propose a simple transform ation of the free-energy curves, which assists in the graphical identificat ion of the glass-forming ranges. (C) 1998 Kluwer Academic Publishers.