Reversible nature of shear bands in copper single crystals subjected to iterative shear of ECAP in forward and reverse directions

摘要

Copper single crystals were subjected to equal-channel angular pressing for two passes via the routes A and C, in order to examine the effect of iterative shear in forward and reverse directions on the development of shear bands in a crystallographic aspect. Shear bands were clearly revealed metallographically after one pass, which accompanies splitting of distinct crystallographic orientations. These shear bands remained after the second pass via route A, where shear was given in a forward direction with regard to the previous shear. Micro-indentation tests show that the shear bands were harder than the matrix, and both the shear bands and the matrix became harder progressively by the second pass. In route C, where the second shear is given in the parallel plane, but in the reverse direction with regard to the previous shear, most of these shear bands were less visible in metallographic and EBSD observations. Besides, the distribution of microhardness became homogeneous across the traces of shear bands and the matrix. It is suggested that the shear bands were dissolved by merging with the matrix by diffusion of the geometrically necessary dislocations (GND) delineating the shear bands and the matrix.