Polycrystalline samples were cyclically deformed, using constant plastic strain amplitudes which ranged from 10-5 to 8 x 10-3. Transmission electron microscopy was used to study the formation of dislocation-free zones beside grain boundaries. It was found that the formation of dislocation-free zones in fatigued polycrystals under low plastic strain amplitudes was very common. It was concluded that grain boundary incompatible stresses which caused the collapse of multi-polar loop patches and walls were responsible for the formation of most dislocation-free zones. For a small number of zones, which were formed in the earliest stages of cyclic hardening, the formation of dislocation-free zones was attributed to the fact that grain boundary incompatible stresses could prevent the formation of multi-polar loop patches beside these grain boundaries.

T.Luoh, C.P.Chang: Acta Materialia, 1996, 44[7], 2683-95