Rearrangement of fatigue dislocation structure in pure aluminum single crystals associated with an increment in deformation temperature

Abstract

Two-step low-cycle fatigue tests of pure Al single crystals with single-slip orientation were performed in the pull-push mode under a constant plastic strain amplitude. In the first-step tests, the plastic strain amplitude within the plateau region of the cyclic stress-strain curve was applied at 77 K. For the second step, the same plastic strain amplitudes were further applied at RT. 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 matrix-vein and PSB-ladder structures after the first-step tests changed into a cell structure. The ladder structure first transitioned to the cell structure the early stages of the second-step test, the volume fraction of the cell structure gradually increased with increasing cumulative shear strain, and then the whole specimen was covered with the cell structure.