Experimental and First-Principles Studies of Phase Stability On the Nb–Ru System

Abstract

The partial phase relationship of Nb–Ru binary system was determined by diffusion couple and equilibrium alloy methods. Two-phase equilibria between Ru2Nb and Ru3Nb were observed at 1373 and 1473 K. Furthermore, the phase stability of Ru2Nb and Ru3Nb was investigated via ab initio calculations. The Ru2Nb with C37 structure and Ru3Nb with Ni3Sn prototype were stable at 1473 K in dynamics and thermodynamics, which were consistent with the experimental results. The second-order phase transition between bcc(Nb) and B2(RuNb) was determined by analyzing the Gibbs energy. The calculation results indicated that the vibrational and electronic contributions to the Gibbs energy were crucial for predicting phase transition. In addition, Nb atoms gained electrons and Ru atoms lost electrons in the ordered structure B2(RuNb), which strengthened the metal bonds and caused the ordered structure more stable than disordered structure bcc(Nb). Finally, the Nb–Ru phase diagram at high temperature was re-constructed based on experimental and calculated results.

Keywords: Nb-Ru system, Phase stability, First-principles calculation, Gibbs energy