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

Experimental investigations of the internal friction and the Young's modulu s defect in single crystals of Cu-(1.3-7.6) at. % Ni have been performed fo r 7-300 K over a wide range of oscillatory strain amplitudes. Extensive dat a have been obtained at a frequency of vibrations around 100 kHz and compar ed with the results obtained for the same crystals at a frequency of simila r to 1 kHz. The strain amplitude dependence of the anelastic strain amplitu de and the average friction stress acting on a dislocation due to solute at oms 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 frequ ency ranges. For the 100 kHz frequency, low temperatures and low strain amp litudes (similar to 10(-7)-10(-5)), the amplitude-dependent internal fricti on and the Young's modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. At hig her strain amplitudes, a transition stage and a steep strain amplitude depe ndence of the internal friction and the Young's modulus defect are observed , followed by saturation at the highest strain amplitudes employed. These s tages are temperature and frequency dependent and are assumed to be due to thermally activated motion of dislocations. We suggest that the observed re gularities in the entire strain amplitude, temperature and frequency ranges correspond to a motion of dislocations in a two-component system of obstac les: weak but long-range ones, due to the elastic interaction of dislocatio ns with solute atoms distributed in the bulk of the crystal; and strong sho rt-range ones, due to the interaction of dislocations with solute atoms dis tributed close to dislocation glide planes. Based on these assumptions, a q ualitative explanation is given for the variety of experimental observation s. (C) 1999 American Institute of Physics. [S0021-8979(99)03802-5].