Thermodynamic Analysis of the Fe–Nb–B Ternary System

Abstract

A thermodynamic analysis of the Fe–Nb–B ternary system has been carried out by estimating the unknown thermodynamic properties of various borides and solid solutions with using a first-principles method. The calculations showed that, at least in the ground state, the solid solution, in which the B atoms substitute for the Fe atoms, was more probable than that where the B atoms dissolved in the octahedral interstitial sites. Furthermore, the calculated values for the binary borides in the Fe–B and Nb–B systems were in reasonable agreement with those found by experiment. The thermodynamic properties such as formation enthalpies for the FeNbB and Nb₃B₂ phases were also determined for ternary borides. The thermodynamic functions determined using these theoretical values, as well as the available experimental information on the phase boundaries, successfully revealed the phase equilibria in the Fe–Nb–B ternary system over the entire composition and temperature ranges.