The evolution of dislocation structure in twins of different thicknesses was investigated in polycrystalline Cu fatigued at room temperature under constant plastic axial strain amplitude control. The dislocation structure and its evolution strongly depended on twin thickness. Three critical thicknesses must be distinguished, i.e. (i) characteristic size of fatigue dislocation structures, about 1µm; (ii) critical height of stable dislocation wall structure, about 200nm; (iii) critical spacing of dislocation dipole, about 20nm. It was considered that the size effect was mainly caused by twin boundaries which played different roles on slip behaviors in twins.

Dislocation Evolution in Twins of Cyclically Deformed Copper. X.L.Guo, L.Lu, S.X.Li: Philosophical Magazine Letters, 2005, 85[12], 613-23