The role of {111} slip in the initial plastic deformation of Ni-base superalloys at room temperature

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After just yielding at room temperature, the deformation mechanisms in the Ni-base superalloys René N5, CMSX-4, PWA 1483, and CM247LC are investigated by transmission electron microscope. It is found that anti-phase boundary shearing controls the initial plastic deformation of René N5, CMSX-4 and PWA 1483, although stacking fault shearing also operates in the latter two alloys. Whereas, besides many pairs of a/2 〈110〉 dislocations, a high density of isolated superlattice stacking faults and extended stacking faults is also created in CM247LC after around 0.2% plastic deformation, indicating that stacking fault shearing prevails in the initial stage of plastic deformation. These observations demonstrate that plastic deformation is not accomplished solely by anti-phase boundary shearing in Ni-base single crystal superalloys at room temperature, and the formation of superlattice stacking faults does not necessarily require reordering of atoms, hence providing new insights into understanding the interaction mechanisms between matrix dislocations and γ' precipitates.