No abstract

The site preference of ternary additions in Ni 3 Nb (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.

The atom substitution preference of ternary additions in Ni 3 M-type GCP (geometrically close-packed) compounds with D0 a structure was determined from the direction of single-phase region of the GCP phase on the reported ternary phase diagrams. In Ni 3 Nb, Co and Cu preferred the substitution for Ni-site, Hf, Ta, Ti, V and W the substitution for Nb-site, and Fe the substitution for both sites. In Ni 3 Ta, Co, Cu, Fe, Ir, Mn and Re preferred the substitution for Ni-site, Mo and Nb the substitution for Ta-site, and Al and Cr the substitution for both sites. In Ni 3 Mo, Pd and W preferred the substitution for Ni-site, and Al, Nb, Ta, Ti and Zr the substitution for Mo-site. The thermodynamic model, which was based on the change in heat of formation of the host compound by a small addition of ternary solute, was applied to predict the atom substitution preference of ternary additions. The heat of compound formation used in the thermodynamic calculation was derived from Miedema's formula. Good agreement was obtained between the thermodynamic model and the result of the literature search. For Ni 3 Mo, with a small negative heat of formation, a weak binding force between the constituent elements is often enhanced by the addition of the ternary elements that substitute for Mo-site.

The site preference of ternary additions in Ni3X-type GCP compounds was determined from the direction of solubility lobe of the GCP phase on the experimentally reported ternary phase diagrams. In Ni3Nb (D0a), Co and Cu preferred the substitution for Ni-site, Ti, V and W the substitution for Nb-site, and Fe the substitution for both sites. In Ni3V (D022), Co preferred the substitution for Ni-site, Cr the substitution for both sites, and Ti the substitution for V-site. In Ni3Ti (D024), Fe, Co, Cu, and Si preferred the substitution for Ni-site, Nb, Mo and V the substitution for Ti-site. 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 result of the literature search was excellent. Both transition and B-subgroup elements have two possibilities, i.e., the case of substitution for Ni-site or the case for X-site, depending on the relative value of two interaction energies.

The site preference of ternary additions in GCP (geometrically close-packed) Ni 3 X-type compounds with D0a structure was determined from the direction of the single-phase region of the D0a phase in the reported ternary phase diagrams. The thermodynamic model based on the Bragg-Williams approximation, which is based on the change in heat of formation of the host compound by a small addition of ternary solute, was applied to predict the site preference of ternary additions. The heat of formation used in the thermodynamic calculation was derived from Miedema's formula. Good agreement was obtained between the thermodynamic model and the result of the literature search.