Electroplastic effect and microstructural mechanism in electrically assisted deformation of nickel-based superalloys

The electroplastic effect and microstructural mechanism in the electrically assisted (EA) deformation of nickel-based superalloys are still not fully elucidated up to now. To this end, the mechanical properties and microstructural evolution of solid solution Inconel 718 alloy were systematically investigated in the EA tension below 600 °C. The experimental results revealed that the electroplastic effect further reduces the deformation resistance by promoting grain rotation and dislocation recovery compared with direct heating. However, the electric current results in the formation of large “bracket-shaped” voids at 600 °C, thereby reducing the elongation. Based on the non-magnetic characteristic of Inconel 718 alloy, the low current density in the EA tension, and the healing effect of current on some elliptical voids, the electroplastic mechanisms are considered as the local Joule heat and the atomic bond weakening due to the electron imbalance near defects. The electroplastic mechanisms were used to analyze further the electroplastic effects on the strengthening mechanisms, dislocation morphology evolution, and fracture mechanism. The electric current weakens the precipitation strengthening, grain boundary strengthening, and dislocation strengthening, but promotes the solid solution strengthening. The unique dislocation morphology with a cross pattern in the EA tensile specimen may be attributed to the weaker mobility of dislocations parallel to the current direction due to the weaker electron imbalance. Moreover, the electron imbalance reduces the strength of the matrix around the carbides, leading to large “bracket-shaped” voids and premature fracture in the EA tension at 600 °C.