The L1₂-ordered Ni₃Al γʹ phase is an archetype example of intermetallic phases and provides high-temperature strength to Ni-based superalloys in aerospace and power generation applications [1]. Substitutional solute additions may prefer replacing Ni on the α sites, and / or Al on the β sites due to interatomic interactions [2]. Such site preferences can be predicted using first-principles studies, but may change with alloy composition and temperature [3]. Importantly, recent modeling predicted significant changes of the mechanical properties, depending on α or β site preference [4]. However, accurate experimental quantification of the element-specific site preference in the γʹ phase remain challenging.
Therefore, this work presents a new experimental method to quantify the site occupancy of substitutional solute additions in the L1₂-ordered Ni₃Al γʹ phase from atom probe tomography data. This is demonstrated in the top, middle, and bottom regions of an electron powder bed fusion produced IN-738LC build. Ti, W, and Ta replace Al on the β sites. Cr and Mo substitute α and β sites, with a preference for the latter. Co also substitutes α and β sites, but with a preference for the former. Changes of the Mo and Co relative site occupancies throughout the build suggest that local changes in the thermal history may influence the site occupancy in the γʹ phase. This is important in multi-component intermetallic phases because of the burgeoning interest in relating mechanical properties of these structures to their site-occupancy.

References:
[1] R. C. Reed, The Superalloys: Fundamentals and Applications, 2006.
[2] R. Eriş et al., Intermetallics, vol. 109, pp. 37–47, Jun. 2019.
[3] Q. Wu & S. Li, Computational Materials Science, vol. 53, no. 1, pp. 436–443, Feb. 2012.
[4] M. Wen et al., Chinese Phys. B, vol. 29, no. 7, p. 078103, Jul. 2020.
[5] B. Lim et al., Additive Manufacturing, vol. 46, p. 102121, Oct. 2021.