Thermodynamic analysis of the Fe-Cr-B ternary system

Abstract

A thermodynamic analysis of the Fe-Cr-B ternary system was carried out to clarify the complex phase equilibria between several types of borides and solution phases. To satisfy the lack of experimental information on thermodynamic properties for this ternary system, a first-principles method was applied to evaluate the enthalpies of formation of binary Cr-boride phases. The calculated enthalpy of formation of CrB2 agreed well with the experimental value. However, the first-principles calculations suggested that the CrB phase is more stable in the ground state than previously thought. Variations of the formation enthalpies of Fe2B (IA/mcm) and CrB (Cmcm) with dissolving Cr and Fe were also evaluated for superstructures constructed by modifying the stack of atoms along a given direction of the parent lattice structures. The thermodynamic parameters of the Fe-Cr-B ternary system were optimized with the CALPHAD technique using these calculated thermodynamic properties along with available experimental information on phase equilibria and some thermodynamic data. We found that the evaluated parameters reasonably reproduced the experimental data on the isothermal sections, the pseudo-binary section, and the liquidus projection in the Fe-rich region.