Experimental determination and thermodynamic optimization of the Nb–V–Zr system

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 analyzing solidification microstructures and phase constituents. The stability of the τ phase with C14-structure was established by investigating the composition range of Nb in τ, which was measured to be between 19.8 and 40.5 at. % at 1473 K. The solubility of Nb in λ2 with the C15-type was ∼ 16.9 at. % 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 diagram data in this work and the literatures. Solution phases, including liquid, bcc, and hcp, were regarded as substitutional solutions. Considering the crystal structures and solid solubility of intermetallic compounds, λ2 and τ were modeled as (Nb,V,Zr)2(Nb,V,Zr) using two-sublattice model. A set of self-consistent thermodynamic parameters of the Nb–V–Zr system was obtained, which will provide theoretical guidance for the design of Zr-based nuclear materials.