THE ROLE OF STRAIN COMPATIBILITY IN THE CYCLIC DEFORMATION OF COPPER BICRYSTALS

In order to improve our understanding of the link between the cyclic deformation of single crystals and of polycrystalline materials, a study was performed on copper bicrystals. Testing under strain control within the high cycle regime was performed in isoaxial [149] (90° and 180°) twist boundaries and [149]/[001] bicrystals, all with boundaries perpendicular to the tensile axis. A Grain Boundary Affected Zone (GBAZ), where multiple slip dominated, appeared when the boundaries developed compatibility stresses. Experiments showed that the behavior of macroscopically compatible bicrystals, 180° boundaries, is approximately similar to that of a monocrystal, whereas the fatigue responses of the other misorientation show a grain boundary effect, which increases the cyclic stress. The strain in each grain of the [149]/[001] sample was measured separately. The plastic deformation in the adjacent crystals oscillated during initial hardening; finally, the soft grain carried approximately five times the plastic strain of the other grain. © 1997 Acta Metallurgica Inc.