Cyclic deformation of pure aluminum single crystals with double-slip orientations

Fully reversed tension–compression fatigue tests were performed on pure aluminum single crystals with the [1 1 2], [1 1 4] and [1 1 2 0] double-slip orientations under constant plastic strain amplitudes in the range of 5 × 10−4 and 1 × 10−2. No stress saturation was obtained at any strain level in the cyclic hardening curves (CHCs). The CHCs were characterized as: initial hardening, intermediate softening and secondary hardening. The degree of the softening was found to be strongly dependent on the stress-axis: the softening stages were significant for the [1 1 2 0] and [1 1 4] specimens, and conversely, indefinable at any plastic strain amplitude for the [1 1 2] specimens. The changes in surface topography were also found to be dependent on the crystal orientation. Characteristic macrobands in the order of several hundred micrometers were formed in the [1 1 2 0] specimens. The appearance of cyclic softening during fatigue deformation in aluminum single crystals is explained in terms of both the activity of cross-slip and the strain localization in the macrobands.