Origin of localizing creep damage in Ni-based single crystal superalloys pre-strained at room temperature

This work investigates mechanisms of irregular microstructure evolution and creep damage localization induced by the prior room-temperature plastic deformation applied to Ni-based single crystal superalloys, AM1 and CMSX-4 Plus, in between solution and aging treatments. Dislocation climb similar to that occurs during the high-temperature low-stress creep is the main mechanism of the microstructure evolution occurring around pre-deformation slip bands, and subsequently leading to the formation of the bands with coarsened γ/γ′ microstructure. Presence of “ready-to-shear” dislocations inside the coarsened γ′ phase is confirmed by a stereo-pair anaglyph of scanning transmission electron microscopy. This native dislocation structure before the high-temperature/low-stress creep test is the origin of creep damage localization observed for the pre-deformed specimens. The comparison of two alloys revealed that magnitude of plastic activity (precipitation coarsening and dislocation development) inside the bands with the coarsened microstructure is notably larger for AM1 what consequently explains the creep properties degradation under all creep conditions.