Dislocation-free zones in fatigued copper polycrystals

Abstract

Copper polycrystals were cyclically deformed at constant plastic strain amplitudes in the range from 10−5 to 8 × 10−3. Transmission electron microscopy was used to study the formation of dislocation-free zones (DFZs) beside grain boundaries. It was found that the formation of DFZs in fatigued copper polycrystals under low plastic strain amplitudes is a very common phenomenon. Grain boundary incompatible stresses which cause the collapse of multipolar loop patches and walls are responsible for the formation of most DFZs. For a small number of DFZs which are formed right from the very early stage of cyclic hardening, their formation is because the grain boundary incompatible stresses can prevent the formation of multipolar loop patches beside these grain boundaries.