Grain boundary modification and plasticization of pure nickel wires via torsion and annealing

Pure nickel wires are conducted to “torsion and annealing” grain boundary modification to study the effect of thermomechanical process (TMP) on grain boundary characteristics and plasticity. Compared with the initial sample, the elongation of the sample subjected to the optimal TMP increases by 103% while its tensile strength only reduces by 1.8%. A new micro index is presented to comprehensively indicate the coupling effect of grain size and grain boundary characteristic distribution on material plasticity. Numerous special boundaries generate during the initial recrystallization stage in TMP. The interfaces between recrystallization nuclei and the adjacent matrixes are basically incoherent Σ3ic boundaries. EBSD and TEM observations manifest that Σ3 boundaries, especially Σ3ic boundaries, have much weaker resistance on dislocation slip compared with random boundaries. The essence of plasticizing by GB modification is to make the material keep in the state that just completes recrystallization and contains as much as Σ3ic boundaries through coordinated TMP. •Propose a new micro index to unitize the effect of grain boundary and grain size.•The interfaces of recrystallization nuclei are mostly incoherent Σ3 boundaries.•Incoherent Σ3 boundary has the weakest blocking effect on dislocation slip.•The essence of plasticization is achieving as much as incoherent Σ3 boundaries.•The elongation can be increased by 103% compared with the initial sample.