Cell and band structures in cold rolled polycrystalline copper

Abstract

The effect of plastic strain on the deformation microstructure has been investigated in polycrystalline copper rolled at room temperature to 5,10,20, and 30% reduction in thickness (equivalent strain 0'06-0'42). Resultsfrom transmission electron microscopy (TEM) observations show that dense dislocation walls (DDWs) and cells develop during the initial stages of cold rolling. Grains having a high density of DDWs are described as high wall density (HWD) structures, and grains having a low density of DDWs are described as low wall density (LWD) structures. These structures are characterised by cell size, misorientation across the cell walls, and the crystallographic orientation of the grains in which they appear. The DDWs in the HWD structures have special characteristics, extending along several cells and having a misorientation across them greater than that across ordinary cell boundaries at the same strain. The DDWs appear to have a macroscopically determined orientation. Analysis of their crystallographic orientation shows that they are not, asfrequently reported in the literature, parallel to {111} planes. It is suggested that the DDWs separate regions of the crystal having different operating slip systems. Two generations of microbands are found to develop with increasing deformation. The first generation microbands are related to a continuous development of the structure according to the principle of grain subdivision, whereas the second generation microbands relate to localised shear on {ill}. Finally, the evolution of the deformation microstructure in copper is compared with that observed in other face centred cubic metals, especially aluminium.MST/1273

On modeling micro-structural evolution using a higher order strain gradient continuum theory

“…Bands of high dislocation density (dislocation walls) typically form webs enclosing regions of relatively low dislocation content (cell interiors). Ananthan et al (1991) report on clear mesh like dislocation structures in cold rolled polycrystalline copper, while the studies of Huang and Winther (2007) and Hong et al (2013) reveal details on dislocation structures and geometrically necessary boundaries in aluminum and copper specimens. Recently, Oztop (2011) performed high resolution electron backscatter diffraction (HR-EBSD) measurements on a nickle single crystal, subject to wedge indentation in an approximate two-dimensional plane strain deformation state.…”

Shear Localization in Crystallographic Bands in Rolled Copper and Brass

“…The investigation of the second-generation microbands is hampered by their structural instability as described in detail by Ananthan et al [2,7]. It is a very common observation in TEM investigations that parts of microbands have vanished.…”

“…In copper rolled to moderate reductions there are two types of grains: grains with an equiaxed cell structure, LWD (low wall density) grains, and grains with a parallelogram-shaped pattern of dislocation walls, HWD (high wall density) grains [7]. Second-generation microbands form preferentially in the former type of grains, but they may also be observed in the latter.…”

Nanostructured Aluminum and IF Steel Produced by Rolling—a Comparative Study

“…1,2) Such principles are, for example, that the structures minimize their energy per unit length of dislocation line 3) and that the grain orientation through the operating slip systems significantly affects the evolution of the deformation microstructure. 4,5) The microstructural evolution during cold rolling has been studied extensively in fcc metals such as Al, 6) Ni 7) and Cu 8) and to a lesser extent in bcc metals such as iron and steel. 9,10) At small strains a cell block structure forms, as shown in Fig.…”