Best-fit ellipsoids of atom-probe tomographic data to study coalescence of γ′ (L12) precipitates in Ni–Al–Cr

An algorithm is presented to fit precipitates in atom-probe tomographic data sets as equivalent ellipsoids. Unlike previous techniques, which measure only the radius of gyration, these ellipsoids retain the moments of inertia and principle axes of the original precipitate, preserving crystallographic orientational information. The algorithm is applied to study interconnected γ′-precipitates (L12) in the γ-matrix (face-centered cubic) of a Ni–Al–Cr alloy. The precipitates are found to coagulate along 〈1 1 0〉-type directions.