Cyclic deformation of al-single crystals at low constant plastic strain amplitudes

Abstract

Cyclic deformation of Al-single crystals with the crystal axis parallel to (1̄23) has been performed at room temperature and at 77 K at plastic shear strain amplitudes in the range 2.4·10 −4−1.2·10 −2. At room temperature, mechanical saturation was not obtained at any strain level, with a possible exception at the very lowest value. Instead, a hardening-softening-secondary hardening sequence was generally found. The hysteresis loops did not change shape during the cycling. At 77 K, mechanical saturation was reached, and the cyclic stress-strain curve had a plateau region in the plastic shear strain amplitude range 4.2·10 −3−1.2·10 −2. The hysteresis loop became more rectangular when saturation was approached, similar to what is found in Cu single crystals. The slip line pattern consisted of macrobands, which were made up by small segments of PSBs on the primary slip plane. Slip activity was also found on other slip systems. The macrobands are explained by considering the nucleation and propagation of PSBs. The dislocation structure formed at 77 K was found to be rather similar to the structure developed in Cu single crystals oriented for single slip. A high density of dislocation loops was found. The ladder structure was not observed.