Synchrotron In-Situ Aging Study and Correlations to the γ′ Phase Instabilities in a High-Refractory Content γ-γ′ Ni-Base Superalloy
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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.
The financial support for this investigation was provided by Rolls-Royce Corporation. The authors thank Saul Lapidus for the help with the synchrotron setup and Dieter Isheim for the useful discussion on the atom probe data. Additionally, use of the Advanced Photon Source at Argonne National Laboratory was supported by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
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