Athermally-enhanced recovery and recrystallization behaviors in cold-rolled pure tungsten via electric current stressing

Abstract

In this study, athermally-enhanced recovery and recrystallization behaviors were introduced in the pure tungsten at 4.8 × 10⁴ A/cm² for 1 h at a processing temperature of 235 °C (0.14 T_m), which was much lower than the conventional heat treatment of approximately 1500 °C. The metallurgical behavior induced by electric current stressing for inducing annealing phenomena was investigated using electron backscatter electron diffraction (EBSD) to explain the observed variations in the mechanical and electrical properties. The electric current stressing induced softening of the pure tungsten with a maximum extent of 22.4 %, which was proposed to be attributed to the synergistic recovery and recrystallization. The current-enhanced recovery behavior can be evidenced by the transformation of subboundaries to low-angle grain boundaries, and the current-enhanced recrystallization behavior can be evidenced by the grain refinement, subboundary transformation to high-angle grain boundaries, formation of annealing rotated Cube texture, and annihilation of dislocations. The electrical resistivity increase with a maximum extent of 29.5 % was explained by the increasing grain boundary density as a result of recrystallization. The electrical annealing can achieve the same effect as conventional heat treatment, exhibiting higher efficiency in reducing the micro-hardness of pure tungsten at a lower processing temperature. Pronounced athermal effects of the electro-treatment were highlighted by the comparisons of microstructures and properties with a designed thermal benchmark experiment using the same thermal history as the electro-treatment to provide solid experimental evidence. The electrical annealing is proposed as a potential alternative to conventional heat treatment featuring more energy-efficient and time-saving for green manufacturing.