Mechanical behaviour and dislocation arrangements of cyclically deformed silicon single crystals

Abstract The mechanical behaviour of single-crystal Si tested in fatigue was investigated under plastic strain amplitude control conditions, at a plastic shear strain rate of 3 × 10−4 s−1 in the temperature range 825–900°C, where the lattice frictional forces are still effective, for plastic strain amplitudes ranging from 6 × 10−4 to 5 × 10−3. Cyclic stress-strain curves exhibit two different stages of hardening and pass through a marked maximum before saturation is reached. The saturation stress is decreased when the strain amplitude per cycle is increased. Scanning electron microscopy observations suggest that strain localization takes place near the maximum stress and beyond. Transmission electron microscopy reveals a variety of dislocation arrangements, the most typical of which are, firstly, regularly spaced elongated braids of edge dipoles, secondly, thicker stripes with dense shells and whose cores contain apparently self-organized secondary dislocations and, thirdly, long rows of prismatic loops. Similarities to and differences from dislocation arrangements observed in fatigued fcc metals are briefly discussed.