Alloying behavior of Ni3M-type GCP compounds

The site preference of ternary additions in Ni3M-type GCP compounds was determined from the direction of solubility lobe of the GCP phase on the ternary phase diagram that have been experimentally reported. In Ni3Nb (D0(a)), 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 (D0(22)), Co preferred the substitution for Ni-site, Cr the substitution for both sites, and Ti the substitution for V-site. In Ni3Ti (D0(24)), 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. From both experimental and theoretical results, it was shown in three Ni3M-type GCP compounds that both transition and B-subgroup elements have two possibilities, i.e., the case of substitution for Ni-site or the case for M-site, depending on the relative value of two interaction energies. (C) 2010 Elsevier B.V. All rights reserved.