Internal friction background and peaking effect

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Abstract
Internal friction results on poly- and single-crystalline samples of 5 N Cu during irradiation at 350 K with 1.5 MeV electrons are presented. It is found that the peaking effect is a function of the total number of point defects created in the lattice and that it is independent of the frequency in the range 102–105 Hz. The amplitude dependence of peaking is shown to be related to the background amplitude dependence. Pulsed irradiation experiments indicate that no diffusion mechanism is involved in the initial increase of internal friction. It is then concluded that peaking is due to two effects, one from the bulk, responsible for the increase and the second, associated to the arrival of point defects at the dislocations and reducing their contribution to damping. The observation of peaking in single crystals at ε?10−6 indicates that sample structure only influences the strain amplitude level at which peaking appears but not its presence. A comparison with existing models allows one to conclude that a lattice dynamics approach provides the most satisfactory description of present results.