Research On Phase Relations Of Fe-Ti-Bi And Fe-Ti-Sn Ternary System

Modifier play an important role in improving the steel microstructure and mechanical properties. Especially a mixture of RE (rare earth) and LMEs(low melting-point elements), it not only eliminates the harmful effects of low-melting impurity elements and also effectively improve the toughness and abrasion resistance and other properties. Phase diagrams and thermodynamics information of related system are important, which help researchers understand the role of elements in the modifier mixture. The present work focuses on experimental investigation about the phase equilibria in Fe-Ti-Bi and Fe-Ti-Sn ternary system and thermodynamic descriptions of the Ti-Bi binary system and Fe-Ti-Bi ternary system.(1) By using alloy sampling, the isothermal section of Fe-Ti-Bi ternary system at773K was determined, where the existence of a ternary phase Bi2FeTi4was confirmed. Three three-phase regions and two two-phase regions were measured.(2) Formation enthalpies of the intermediate phases BiTi2, Bi9Ti8and 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 bereasonably explained.(3) The isothermal section of Fe-Ti-Sn ternary system at1073K was investigated combining with electron probe microanalysis (EPMA) and X-ray diffraction (XRD) analysis. The existence of nine three-phase regions and five two-phase region were confirmed. Equilibrium relationship between Fe-Ti-Sn ternary1073K under. The isothermal section of Fe-Ti-Sn ternary system at1073K was constructed.