An Oriented Recrystallization Nucleation Mechanism of a Cold-Rolled Pure Ti with Electric-Pulse Treatment

The effect of electric-pulse treatment (EPT) on the nucleation behavior of a cold-rolled pure Ti was investigated. The specimens are subjected to EPT and then annealed at 650 °C within 10 min. Both the electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques were used for detailing the microstructural evolution of the specimens at the initial stage of recrystallization processing during annealing. The results show that oriented nucleation occurs in the EPTed specimen. The recrystallized grains form in a similar orientation with the deformed matrix grains, and the oriented nucleation originates from the deformed grains with <0001> poles tilted about 20° away from the normal direction (ND20 grains) in the EPTed specimen. Pyramidal <c + a> dislocations could be extensively activated in ND20 grains, while the activated dislocations were mainly on prismatic planes in the other oriented grains. Because the formation of sub-grains cannot be without the pyramidal <c + a> dislocation, oriented recrystallized grains easily form in the EPTed specimen. It is suggested that the increasing of pyramidal dislocation climbing activity is considered the key mechanism of the formation of sub-grains as well as oriented nucleation, resulting from high contents of vacancy induced by EPT.