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

Abstract

The nucleation behavior of a cold-rolled pure Ti subjected to the electric-pulse treatment (EPT) and then annealing at 650℃ within 10 minutes was investigated. Both the electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques were used for the detail 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 the similar orientation with the deformed matrix grains and 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 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 dislocation, oriented recrystallized grains easily from in the EPTed specimen. It is suggested that the increasing of pyramidal dislocation climbing activity is considered as the key mechanism of the formation of sub-grains as well as oriented nucleation, resulting from high contents of vacancy induced by EPT.

Keywords: Oriented nucleation mechanism, Pure Ti, Electric-pulse treatment, Annealing, Pyramidal dislocation.