Alloying Behavior of Ni₃Nb

Abstract

The site preference of ternary additions in Ni₃Nb (D0_a) was determined from the direction of solubility lobes of the GCP phases which were available from the reported ternary phase diagrams and constructed in the present work. It was shown that Cr, Co and Cu preferred the substitution for Ni-site, Ti, V, Hf, Ta and W the substitution for Nb-site, and Fe the substitution for both sites. The thermodynamic model, which was based on the change in total bonding energy of the host compound by a small addition of ternary solute, was applied to predict the site preference of ternary additions. The bond energy of each nearest neighbor pair used in the thermodynamic calculation was derived from the heat of compound formation by Miedema’s formula. The agreement between the thermodynamic model and the experimental result was excellent. From both experimental and theoretical results, both the transition and B-subgroup elements have two possibilities, i.e., the case of substitution for Ni-site or the case of substitution for Nb-site, depending on the relative value of two interaction energies.