Low angle boundary migration of shot‐peened pure nickel investigated by electron channeling contrast imaging and electron backscatter diffraction

Abstract

Study on recrystallization of deformed metal is important for practical industrial applications. Most of studies about recrystallization behavior focused on the migration of the high‐angle grain boundaries, resulting in lack of information of the kinetics of the low angle grain boundary migration. In this study, we focused on the migration of the low angle grain boundaries during recrystallization process. Pure nickel deformed by shot peening which induced plastic deformation at the surface was investigated. The surface of the specimen was prepared by mechanical polishing using diamond slurry and colloidal silica down to 0.02 μm. Sequential heat treatment under a moderate annealing temperature facilitates to observe the migration of low angle grain boundaries. The threshold energy for low angle boundary migration during recrystallization as a function of misorientation angle was evaluated using scanning electron microscopy techniques. A combination of electron channeling contrast imaging and electron backscatter diffraction was used to measure the average dislocation density and a quantitative estimation of the stored energy near the boundary. It was observed that the migration of the low angle grain boundaries during recrystallization was strongly affected by both the stored energy of the deformed matrix and the misorientation angle of the boundary. Through the combination of electron channeling contrast imaging and electron backscatter diffraction, the threshold stored energy for the migration of the low angle grain boundaries was estimated as a function of the boundary misorientation.

Microstructure Evolution and Mechanical Properties Improvement of AlZnMgCu Alloys Induced by a Novel Double Electroshocking Treatment

“…However, with large misorientation, LAGBs are prone to migrate and gradually transform into the high angle grain boundaries during the heating process. The migrations which must satisfy thermodynamic principle can be given according to Arrhenius type dependence as follows [34]…”

“…Because of α dp /α ed ( 1, hot dislocations are formed due to hot electrons. [34] Therefore, the temperature inside the material is unevenly distributed in the process of D-EST. Figure 12 shows schematic diagrams of grain boundary temperature distribution at different states.…”