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

In order to improve our understanding of the link between the cyclic d eformation of single crystals and of polycrystalline materials, a stud y was performed on copper bicrystals. Testing under strain control wit hin the high cycle regime was performed in isoaxial [(1) over bar 49] (90 degrees and 180 degrees) twist boundaries and [(1) over bar 49]/[0 01] 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. Experi ments showed that the behavior of macroscopically compatible bicrystal s, 180 degrees boundaries, is approximately similar to that of a monoc rystal, whereas the fatigue responses of the other misorientations sho w a grain boundary effect, which increases the cyclic stress. The stra in in each grain of the [(1) over bar 49]/[001] sample was measured se parately. The plastic deformation in the adjacent crystals oscillated during initial hardening; finally, the soft grain carried approximatel y five times the plastic strain of the other grain. (C) 1997 Acta Meta llurgica Inc.