Cyclic deformation behavior in pure Cu with growth-in twins

A polycrystalline pure copper sample with high density of growth-in twins was synthesized by means of electro-deposition technique. Symmetrical push–pull cyclic deformation was performed at constant axial plastic strain amplitude in the range of 1.1 × 10−4 ≤ ɛpl ≤ 3.9 × 10−3. At low strain amplitudes (ɛpl = 1.1 × 10−4, 2.1 × 10−4), the initial cyclic hardening of Cu sample was found to be similar to that of single crystal Cu, and secondary softening was found. At higher strain amplitudes (ɛpl = 1.0 × 10−3, 1.8 × 10−3), cyclic stress reached the saturation rapidly, neither secondary softening nor secondary hardening was found. Investigations of dislocation configurations show that twin boundaries play a crucial role in the plastic deformation at higher strain amplitudes for Cu. A special wall structure, i.e. persistent slip bands (PSB)-like structure, was found inside the twin lamellae, which may induce the saturation cyclic behavior in Cu.