Geometrically necessary boundaries and incidental dislocation boundaries formed during cold deformation

Abstract

The evolution of microstructure during plastic deformation has recently been described in terms of grain subdivision involving the formation of rotated volume elements. These elements are ordinary dislocation cells and cell blocks where a cell block contains from one to several cells. The cell blocks are bounded by dislocation boundaries which accommodate the lattice misorientation between neighboring cell blocks which deform with different slip system combinations and/or by different amount of shear. The boundaries which accommodate these lattice misorientations are called geometrically necessary boundaries or GNBs. The ordinary cells are also bounded by dislocation boundaries which, however, form as a result of statistical trapping of glide dislocations supplemented by unpredicted dislocations. These boundaries have been called incidental dislocation boundaries of IDBs. The formation and characteristics of the two types of boundaries was discussed and it was suggested that: (i) the misorientation across GNBs should typically be much larger than across IDBs and should rise faster with increasing strain, and (ii) the influence on the flow stress should be different for the two types of boundaries. The present study was initiated to examine the validity of the first suggestion by characterizing the deformation structure in terms of boundary type and bymore » analyzing the boundaries by measuring their spacing and their angular misorientation as a function of the plastic strain. Pure aluminum rolled at room temperature has been used by way of example.« less