Dislocation structures in cyclically deformed copper bicrystals

Two types of symmetrical copper bicrystals, designated as [135]/[135] and [235]/[235], were cyclically deformed at constant shear strain amplitudes (γp1) in the range from ~1.7 × 10−4 to ~9.1 × 10−3. Observations showed that the dislocation structures in the plateau regions of the cyclic stress-strain (CSS) curves of the bicrystals are mainly composed of the ladders of persistent slip bands (PSBs) and the loop patches of matrix. However, additional structure types, such as cells, are present at the high end of plateau in the [–35]/[–35] bicrystal. Above the plateau, the dislocation structures are characterized by cells or labyrinths. The dislocation structures in the vicinity of grain boundary were found to be basically similar to those in the bulk of the fatigued bicrystals. Dislocation-free-zones beside grain boundaries were seldom formed under low strain amplitudes and PSBs were observed to become irregular or taper to a point when approaching to a grain boundary.