Phase equilibria and multi-element interaction study in the metal-rich side of the Nb–Ti–Si–Al quaternary system

The knowledge of phase diagram is theoretical principle for compositional design. Since Ti and Al are important alloying elements for Nb–Si alloys, and Nb and Si are important alloying elements for Ti–Al alloys, Nb–Ti–Si–Al phase equilibria is prerequisite for optimal microstructural design of both Nb–Si and Ti–Al systems. In this work, key alloys were selected firstly according to calculated isothermal section based on extrapolated thermodynamic description, then key alloy ingots were prepared by arc-melting and heat treated to reach equilibrium state. Currently obtained phase equilibria data coupled with critically reviewed literature data were employed to study the element interaction of relative phases (α-Nb₅Si₃, β-Nb₅Si₃, Ti₅Si₃, Nb₃Al and TiAl et al.) in the Nb–Ti–Si–Al system. Thermodynamic parameters of these phases were modified accordingly to reproduce the determined phase relationships. Finally, the important phase equilibria features of the Nb–Ti–Si–Al system were described with several isothermal sections. The phase equilibria extending from ternary systems and new phase equilibria appearing in the quaternary space were demonstrated in this work.