Small-angle neutron scattering from fatigued copper single crystals

Copper single crystals oriented for single and multiple slip were studied by small-angle neutron scattering (SANS) after fatigue tests at a constant plastic shear strain amplitude y γ pl = 0.15% . For the SANS measurements, a special sample holder was used in order to obtain more reliable information about the small differences in the neutron scattering from individual samples. The size of the voids in the samples oriented for single slip increased as a function of the number of fatigue cycles, varying from 0.74 nm to 0.91 nm, but the volume fraction remained more or less constant. The dislocation density observed by SANS was found to increase from 6 × 10 7 mm −2 at τ max/2 to 4 × 10 8 mm −2 at τ max, but remained constant in the saturation stage of cyclic strain hardening. The SANS results obtained are in good agreement with positron annihilation data and transmission electron microscopy observations from the same specimens.