Rearrangement of fatigue dislocation structure in copper single crystals associated with reduction in the plastic strain amplitude

Abstract

Two-step low-cycle fatigue tests of pure Cu single crystals with single-slip orientation were performed in pull-push mode under a constant plastic strain amplitude. In the first-step tests, plastic strain amplitudes larger than that in the plateau region of the cyclic stress-strain curve were applied. For the second step, smaller plastic strain amplitudes in the plateau region were further applied. In the first step, the stress amplitude showed cyclic hardening to saturation. On the other hand, stress amplitude in the second step gradually decreased with increasing cumulative plastic shear strain and transformation of the dislocation structure occurred. Well-developed cell and labyrinth structures after the first-step tests changed into a ladder structure that is characteristic of formation of persistent slip bands (PSBs). The ladder structure started to form in the early stages of the second-step test and the dislocation wall spacing of the ladder structure gradually increased with increasing cumulative shear strain. From these results, it is concluded that the cell and labyrinth structures were rearranged into the PSB ladder structure by reducing the plastic shear strain amplitude.