Strain amplitude-dependent anelasticity in Cu–Ni solid solution due to thermally activated and athermal dislocation–point obstacle interactions

Abstract

Experimental investigations of the internal friction and the Young’s modulus defect in single crystals of Cu-(1.3–7.6) at. % Ni have been performed for 7–300 K over a wide range of oscillatory strain amplitudes. Extensive data have been obtained at a frequency of vibrations around 100 kHz and compared with the results obtained for the same crystals at a frequency of ∼1 kHz. The strain amplitude dependence of the anelastic strain amplitude and the average friction stress acting on a dislocation due to solute atoms are also analyzed. Several stages in the strain amplitude dependence of the internal friction and the Young’s modulus defect are revealed for all of the alloy compositions, at different temperatures and in different frequency ranges. For the 100 kHz frequency, low temperatures and low strain amplitudes (∼10−7–10−5), the amplitude-dependent internal friction and the Young’s modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. At higher strain amplitudes, a transition stage and a steep strain amplitude dependence of the internal friction and the Young’s modulus defect are observed, followed by saturation at the highest strain amplitudes employed. These stages are temperature and frequency dependent and are assumed to be due to thermally activated motion of dislocations. We suggest that the observed regularities in the entire strain amplitude, temperature and frequency ranges correspond to a motion of dislocations in a two-component system of obstacles: weak but long-range ones, due to the elastic interaction of dislocations with solute atoms distributed in the bulk of the crystal; and strong short-range ones, due to the interaction of dislocations with solute atoms distributed close to dislocation glide planes. Based on these assumptions, a qualitative explanation is given for the variety of experimental observations.