By using state-of-the-art characterisation techniques including atom probe tomography and atomic resolved elemental mapping

we successfully probed the site occupation evolution associated with composition change in γ′

during 1100°C creep of a fourth generation Ru-bearing Ni-based superalloy. It is quantified that

W and Ru maintain unchanged site preference after creep rupture

while interestingly

the rest elements especially Co

Ta and Re show a weakened preference at both α- and β-sites in the γ′ lattice. This indicates the overall reduced γ′ ordering degree and thus the possible decrease in planar fault energies

which further facilitates dislocation shearing in γ′.