Site Preference of the Alloying Additions on Mechanical Properties of L1₂ Ni₃Co Alloys

The site preference and alloying effects of transition metal elements M (M = W, Nb, Ta) on mechanical properties of L1₂ NiCo-based alloys are investigated by density functional theory. The formation enthalpy (ΔH_f) and substitution formation enthalpy (\( E_{\text{site}} \)) are calculated to prediction the site preference of elements M. The results indicate that the three elements all tend to replace Ni site. The mechanical properties (elastic properties and hardness) calculations show that the alloying elements deteriorate the ductility and remarkably improve the hardness of the Ni₃Co alloys. Ni₂₃NbCo₈ possesses the lowest ductility and the highest hardness. Ni₂₃TaCo₈ displays the highest shear modulus (G) and Young’s modulus (E). The anisotropic factors, 3D directional Young’s modulus, predict Ni₂₃MCo₈ alloys are all anisotropic materials, and the degree of anisotropy is small. Further analyses on electron localization function (ELF) demonstrate that mechanical properties are closely connected with the bonding nature of the alloys.