Physicochemical laws of the interaction of nickel aluminides with alloying elements: I. Formation of nickel aluminide-based solid solutions

Physicochemical interactions in Ni-Al-M, where M is an alloying element (metal or metalloid), have been systematically analyzed. In most cases, the order of the solubilities of alloying elements (AEs) in the nickel aluminides β-NiAl and γ′-Ni3Al (with an ordered crystal lattice) and the character of substitution of AEs for the positions of Ni (Group VIIIA electronegative transition metal with the valence-electron configuration d 8 s 2 and atomic radius r at = 0.124 nm) and/or Al (Group IIIA electropositive nontransition s 2 p 1 metal with atomic radius r at = 0.143 nm) in these aluminides can be satisfactorily explained using the positions of these elements in the periodic system, the atomic radii of the isolated elements, and their outer electron configurations. The study of β-NiAl-based solid solutions demonstrates that the transition of the sp electrons of Al to the d band of transition metals changes the effective atomic radii of both Al and the transition metals. As a result, the ratio of their atomic radii can change. A correlation has been established between the ability of AE atoms to substitute for Ni and Al atoms in the crystal lattice of the intermetallic compound β-NiAl or γ′-Ni3Al and the effective atomic radii of the components of solid solutions. The use of the effective atomic radii of the solution components to estimate the atomic-size misfit makes it possible to take into account the atomic radii of pure components and their changes as a result of chemical interaction in a solid solution caused by electron redistribution. These changes depend on the position of an AE in the periodic table. This approach explains some contradictions that appear when the shape of a homogeneity area and the solubility of the AE in β-NiAl or γ′-Ni3Al are related to the atomic radii of pure components.