Defect interactions and formation of nanometer γ phases within γ' precipitates in Ni-Co-based superalloys during creep

Interactions between different stacking faults (SFs) and microtwins (MTs) in γ' precipitates within Ni-Co-based superalloys during creep were investigated with atomic resolution. And significant segregation of Co and Cr was detected at SF-SF, SF-MT and MT-MT intersections in γ' precipitates within samples crept at intermediate temperatures (680–750 °C) under different stresses. Local concentration of γ' formers (Al and Ti) were decreased below 10 at.% which is too low to stabilize chemically ordered γ' phase at such intersections. Localized transformation from chemically ordered γ' to disordered γ was confirmed by atomic-resolution imaging. Quantitative analyses indicated that pipe diffusion along interfacial dislocations should play an important role in facilitating localized γ'-to-γ transformation. Formation of γ nanorods/nanoplates along those intersections within γ' precipitates can impede glide of twinning dislocations and superlattice dislocations, which can consequently play a role in resisting creep deformation of the alloy.