The behaviors and mechanisms of current-enhanced recrystallization and grain growth in as-rolled pure nickel during electrical annealing

Abstract

This study investigated the metallurgical behaviors and mechanisms induced by electrical annealing in as-rolled pure nickel, with a focus on the relationships among microstructure, micro-hardness, and electrical resistivity. Direct current stressing at 3.00–3.30 × 10⁴ A/cm² for 1 h induced significant micro-hardness reduction (up to 35.4 %) and electrical resistivity (up to 9.9 %). Comprehensive electron backscattered diffraction (EBSD) analyses revealed progressive recrystallization and grain growth due to enhanced grain boundary migration, characterized by grain size increase, transformation of subboundaries and low-angle grain boundaries into high-angle grain boundaries and Σ3 60°<111> ATBs, relief of residual stress and dislocation annihilation; and transformation of Copper-type rolling textures (Copper, Brass, and Goss) into Cube-oriented recrystallization texture with retained S components. Threshold behaviors for microstructure and property changes occurred at current densities in a narrow transition range. The quantitative analyses further reveal declines in the micro-hardness contributions from normal grain boundaries (59.2 %), ATBs (52.6 %), and dislocations (36.1 %), supporting superior thermodynamic stability of ATBs. Comparative thermal annealing benchmark using identical thermal history as electrical annealing highlighted the dominant role of athermal effects under electric current stressing. Current-enhanced recrystallization and grain growth for the observed micro-hardness reduction are predominantly driven by athermal effects, while thermally activated recovery is more governed by thermal effects. Finally, energy consumption estimations reveal that electrical annealing achieved superior metallurgical effects with over 99 % lower energy than conventional thermal annealing. These results suggest that electrical annealing offers a highly efficient and effective alternative for processing nickel-based metals, at significantly lower temperatures.