Fatigue testing of single crystalline silicon

This study reports the first evidence of persistent slip bands (PSB) in single crystalline silicon tested in fatigue. Experiments have been carried out in a temperature domain where lattice friction forces are still effective, e.g. 1123–1173 K. Besides seven samples that showed continuous hardening in function of cumulative stress, two samples reached a maximum stress followed by an asymptotic decrease. The peak stress in the cyclic hardening curve is attained after 4700 cycles, for a strain amplitude of 4×10−3. Preliminary transmission electron microscopy (TEM) observations revealed dislocations arranged in ladder-like structures. The most striking difference between these structures and the ones reported for fcc metals such as Cu or Ni concerns the dislocation density that is much lower in the case of Si. Although crystals were orientated for single slip, at least two slip systems have been activated in the samples that reached mechanical saturation.