Amplitude-dependent internal friction, microplastic strain and recovery of lead at ambient temperature

Damping properties and the influence of plastic prestrain on microplastic behaviour of polycrystalline lead have been studied by internal friction. Measurements were performed in the infraand ultrasonic ranges. Infrasonic tests were combined with high-resolution registration of the microplastic strain. The strain amplitude dependence of internal friction shows two stages characterized by different recovery times. These stages are attributed to different mechanisms: dislocation — point defect interaction at moderate oscillatory strain amplitudes and dislocation — dislocation interaction at high amplitudes. A pronounced and nonmonotonic dependence of the amplitude-dependent internal friction (ADIF) and elastic limit on prestrain is revealed. Prestraining up to 10% suppresses the ADIF in the ultrasonic range and causes a considerable increase of the elastic limit in the infrasonic range. A further prestrain up to 30% is accompanied by a drastic increase of the ultrasonic ADIF and a pronounced fast softening of lead in the micro- and macroplastic ranges. The conclusion has been drawn that ortho-and metarecovery occur intensively in lead after high prestrain. These processes are ascribed, respectively, to a decrease in net dislocation density and to a transition from a relatively homogeneous dislocation distribution to an inhomogeneous one.