Abstract
The analytical limitations in atom probe tomography such as resolving a desired set of atomic
planes, for solving complex materials science problems, have been overcome by employing a
well-developed unique and reproducible crystallographic technique, involving synergetic
coupling of orientation microscopy with atom probe tomography. The crystallographic
information in atom probe reconstructions has been utilized to determine the solute site
occupancies in Ni-Al-Cr based superalloys accurately. The structural information in atom probe
reveals that both Al and Cr occupy the same sub-lattice within the L12-ordered g’ precipitates to
form Ni3(Al,Cr) precipitates in a Ni-14Al-7Cr(at.%) alloy. Interestingly, the addition of Co,
which is a solid solution strengthener, to a Ni-14Al-7Cr alloy results in the partial reversal of Al
site occupancy within g’ precipitates to form (Ni,Al)3(Al,Cr,Co) precipitates. This unique
evidence of reversal of Al site occupancy, resulting from the introduction of other solutes within
the ordered structures, gives insights into the relative energetics of different sub-lattice sites
when occupied by different solutes.
