Fatigue testing of monocrystalline Si was performed at 800 to 900C using strain rates of 1.5 x 10-4 to 6 x 10-4/s; within which lattice friction was still effective. Tension–compression loading was applied under plastic strain amplitude control. For plastic strain amplitudes ranging from 6 x 10-4 to 10-2, cyclic stress–strain curves exhibit 2 different stages of hardening and pass through a maximum before saturation was reached. At variance from what was observed in metals, the saturation and maximum stresses were decreased when the strain amplitude per cycle was increased. Microscopic observations suggested that strain localization takes place near the maximum cyclic stress and beyond. Several types of dislocation arrangement were revealed by transmission electron microscopy observations. Before mechanical saturation, edge dislocation dipoles sit mainly in thick rectilinear walls. When observed perpendicularly, these walls form either linear or corrugated arrangements. Once the maximum stress was reached, it seems that part of the microstructure ceases to participate in the imposed deformation while other regions concentrate it. In the former case, the dislocation structure anneals and a loop structure was created from the dipolar walls. In the latter case, active dislocation walls condense in much thinner walls, similarly to what was observed in the persistent slip bands in face-centered cubic metals, but deformation bands in Si were much wider.

Fatigue Testing and the Evolution of the Defect Microstructure in Si Single Crystals by Transmission Electron Microscopy. M.Legros, O.Ferry, J.P.Feiereisen, A.Jacques, A.George: Journal of Physics - Condensed Matter, 2002, 14[48], 12871-82