High-temperature site preference and atomic short-range ordering characteristics of ternary alloying elements in gamma '-Ni3Al intermetallics

Remarkable high-temperature mechanical properties of nickel-based superalloys are correlated with the arrangement of ternary alloying elements in L1(2)-type-ordered. gamma '-Ni3Al intermetallics. In the current study, therefore, hightemperature site occupancy preference and energeticstructural characteristics of atomic short-range ordering (SRO) of ternary alloying X elements (X = Mo, W, Ta, Hf, Re, Ru, Pt or Co) in gamma '-Ni3Al 21.875 X 3.125 alloy systems have been studied by combining the statistico-thermodynamical theory of ordering and electronic theory of alloys in the pseudopotential approximation. Temperature dependence of site occupancy tendencies of alloying X element atoms has been predicted by calculating partial ordering energies and SRO parameters of Ni-Al, Ni-X and Al-X atomic pairs. It is shown that, all ternary alloying element atoms (except Pt) tend to occupy Al, whereas Pt atoms prefer to substitute for Ni sub-lattice sites of Ni 3 Al intermetallics. However, in contrast to other X elements, sublattice site occupancy characteristics of Re atoms appear to be both temperature-and composition-dependent. Theoretical calculations reveal that site occupancy preference of Re atoms switches from Al to both Ni and Al sites at critical temperatures, T c, for Re > 2.35 at%. Distribution of Re atoms at both Ni and Al sub-lattice sites above T c may lead to localised supersaturation of the parent gamma '-Ni3Al phase and makes possible the formation of topologically close-packed (TCP) phases. The results of the current theoretical and simulation study are consistent with other theoretical and experimental investigations published in the literature.

Citation Formats
R. Eriş, A. Mehrabov, and M. V. Akdeniz, “High-temperature site preference and atomic short-range ordering characteristics of ternary alloying elements in gamma ’-Ni3Al intermetallics,” PHILOSOPHICAL MAGAZINE, vol. 97, pp. 2615–2631, 2017, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/46335.