The role of annealing twin boundaries in the cyclic deformation of f.c.c. materials

Detailed transmission electron microscopy (TEM) studies have been carried out in order to examine the role of annealing twin boundaries in the cyclic deformation of ramp-loaded polycrystalline copper. It is found that regions adjacent to the twins are preferred sites for earlier formation of persistent slip bands (PSBs). Furthermore, steps at twin boundaries and twin tips enhance early operation of secondary slip and these features have been identified as critical places for promoting the nucleation of PSBs. Finally, a close relationship is established in high cycle fatigue between cyclic deformation, in the bulk, and crack initiation, in the surface, in regions close to twins. Such behavior is correlated with localization of deformation within the PSBs which form earliest in life, and can be generalized to f.c.c. polycrystals that contain twins.