Thermodynamic modeling of Fe-Ti-Bi system assisted with key experiments

Phase equilibria of Fe-Ti-Bi ternary system have been studied in this work. Firstly, by using alloy sampling, the isothermal section of Fe-Ti-Bi ternary system at 773 K was determined, where the existence of a ternary phase Bi2FeTi4 was confirmed. Meanwhile, formation enthalpies of the intermediate phases BiTi2, Bi9Ti8 and Bi2FeTi4, were obtained with first-principles calculations. Based on experimental data of phase equilibria and thermodynamic properties in literatures along with the calculated formation enthalpies in this work, thermodynamic modeling of Ti-Bi binary system and Fe-Ti-Bi ternary system were carried out with the CALPHAD approach. A set of self-consistent thermodynamic parameters to describe the Gibbs energy for various phases in Fe-Ti-Bi ternary system was finally obtained, with which solidification processes of two typical Fe-Ti-Bi alloys could be reasonably explained.