Experimental Determination and Thermodynamic Optimization of the Nb–V–Zr System

Abstract

A comprehensive thermodynamic description for each phase is essential for designing of the novel Zr-based nuclear materials. The construction of the experimental liquidus surface projection and isothermal section of the Nb–V–Zr system was established through the analyses of solidification microstructures and phase constituents. The stability of the τ phase was established by investigating the range of Nb compositions in τ, which was measured to be between 19.8 and 40.5 at. %, and ~ 16.9 at. % in λ2 at 1473 K. The liquidus surface projection showed primary solidification areas of bcc(Nb,V,Zr), λ2 and τ. The thermodynamic parameters were derived combining the CALPHAD method with experimental results from phase equilibrium data. Solution phases, including liquid, bcc, and hcp, were regarded as substitutive solutions, while the crystal structures and solid solubilities of intermetallic compounds were considered in modeling λ2 and τ as (Nb,V,Zr)2(Nb,V,Zr). The thermodynamic properties of the Nb–V–Zr system were analyzed to offer theoretical guidance for the advancement of Zirconium nuclear materials.

Keywords: Nb-V-Zr system, Liquidus surface projection, microstructure, CALPHAD method