Rearrangement of fatigue dislocation structure in a pure-aluminium single crystal associated with change in deformation temperature

Abstract

ABSTRACT A two-step low-cycle fatigue test on a pure-aluminium single crystal with a single-slip orientation was performed in the full pull–push mode under constant plastic shear-strain amplitude. In the first-step test, a plastic-shear-strain amplitude of 5 × 10-3 within the plateau region of the cyclic stress–strain curve was employed at 77 K. In the second-step test, similar plastic-shear-strain amplitude was employed at room temperature. In the first-step test, the shear-stress amplitude showed initial hardening to saturation. However, in the second-step test, it gradually decreased with an increase in the cumulative plastic-shear strain. After the first-step test, the matrix-vein structure and persistent slip bands (ladder structure) were well developed. The ladder structure transformed into the cell structure in the initial stage of the second-step test, the area fraction of the cell structure gradually increased with an increase in the cumulative plastic shear-strain, and the specimen was entirely covered with the well-developed cell structure at the end of the second-step test.