Synchrotron In-Situ Aging Study and Correlations to the γ′ Phase Instabilities in a High-Refractory Content γ-γ′ Ni-Base Superalloy

Detailed ex-situ electron microscopy and atom probe tomography (APT) were combined with in-situ synchrotron diffraction to systematically quantify the chemical, morphological, and lattice instabilities that occur during aging of a polycrystalline high-refractory content Ni-base superalloy. The morphological changes and splitting phenomenon associated with the secondary γ′ precipitates were related to a combination of discrete chemical composition variations at the secondary γ′/γ interfaces and additional chemical energy arising from γ precipitates that form within the secondary γ′ particles. The compositional phase inhomogeneities led to the precipitation of finely dispersed tertiary γ′ particles within the γ matrix and secondary γ particles within the secondary γ′ precipitates, which, along with surface grooving of the secondary γ′ particles, likely due to a spike in the lattice misfit at the particle interfaces, contributed to the splitting of the precipitates during aging.