Thermodynamic Modeling and Solidified Microstructure in the Mo–Nb–Zr Ternary System

An attempt to model the Mo–Nb–Zr ternary system using CALPHAD (CALculation of PHAse Diagram) methodology was performed in this work. The solution phases including liquid, bcc_A2 and hcp_A3 were modeled by substitutional solution model, and the Laves phase was modeled using a two sublattice model. The large solubility of Nb in the binary Laves phase (Mo2Zr) was considered in the sublattice model. This thermodynamic modeling contains all the essential procedure of the CALPHAD methodology. A set of self-consistent thermodynamic parameters for the Mo–Nb–Zr system was obtained. Experimental investigations for the primary crystallization fields were conducted to illustrate the reliability of this thermodynamic description. Primary crystallization phase analysis was performed with the aid of electron probe microanalysis and X-ray diffraction. The observed experimental microstructures were also validated by means of Scheil solidification simulation. The calculated isothermal sections, vertical sections and liquidus projection superimposed with the experimental information were presented in this work.