Thermodynamic Analysis of the Nb–Ti–B Ternary Phase Diagram

A thermodynamic analysis of the Nb–Ti–B ternary system was carried out by estimating the unknown thermodynamic properties of binary and ternary borides by using a first-principles method. The calculated value for the binary TiB2 phase was in reasonable agreement with those found by experiment. Due to a lack of experimental values concerning thermodynamic properties of the ternary system, the formation enthalpies for the Nb3B2–Ti3B2, NbB–TiB (Cmcm), NbB–TiB (Pnma), Nb5B6–Ti5B6, Nb3B4–Ti3B4, and NbB2–TiB2 pseudo-binary sections were also determined by constructing various kinds of superstructures for binary borides. The thermodynamic functions determined using these theoretical values, as well as the available experimental information on the phase fields, successfully revealed the phase equilibria in the Nb–Ti–B ternary system across the entire composition and all temperature ranges. [doi:10.2320/matertrans.MC200820