Extraordinary effect of the δ phase on the electrically-assisted deformation responses of a Ni-based superalloy

The effect of the δ phase (Ni₃Nb) on the electrically-assisted (EA) deformation responses, particularly stress, elongation and dislocation distribution, of the Ni-based superalloy is still unknown up to now, though it is clear as nonnegligible on the quasi-static and hot deformation processes. Therefore, the effect of the δ phase during the electrically-assisted tension were experimentally investigated and analyzed with comparison to that in the hot tension process. Generally, the δ phase existing in the Ni-based superalloy always causes the reduction of flow softening and elongation during cold and the initial stage of hot tension processes. What is distinct, the δ phase promotes the flow softening effect and elongation during the EA tension. In addition, the dislocation-free ring around the δ phase was firstly observed during the EA tension. The mechanism of these macro and micro extraordinary phenomena is concluded as that the δ phase causes serious lattice distortion and dislocation pile-up around itself, which leads to an extremely high temperature due to the local Joule heating effect. The faster elimination of dislocation pile-up in the local area because of the local higher temperature results in the dislocation-free ring phenomenon and the significant improvement of flow softening effect and elongation.