Dislocation damping in Cu-Ni alloys at low temperatures and high strain amplitudes

Abstract

Dislocation damping was studied in 〈110〉 Cu crystals containing 0≲c0≲4×10−2 atom fraction Ni at 95≲T≲297 °K, strain amplitudes ε0 from the mid-10−7 to the mid-10−4 range, and frequencies f≈22 kHz. Dislocation interactions with the combined Suzuki-Cottrell atmosphere are analyzed to explain the composition dependence and propose a model for amplitude-independent damping Q−1I in alloys consisting sequentially of (1) the fault narrowing, (2) the escape of one partial, and (3) the complete breakaway from the combined Suzuki-Cottrell atmosphere. Consideration of both the multiplicity of Cottrell pinning sites and the stacking-fault width demonstrate the role of the pinning-point amplification factor in determining the impurity-dislocation binding energy and the distribution of impurities in the combined atmosphere. The transition ε0 from Q−1I to amplitude-dependent damping Q−1H showed a linear correlation with the calculated Suzuki yield stress. Two distinct stages of Q−1H were observed: at the lower ε0, Q−1H1 is thermally activated and characterized by an escape enthalpy of ≈0.04 eV, while at the higher ε0, Q−1H2 is nearly independent of temperature. A qualitative static-hysteresis model is proposed to account for the interaction between dislocations in the breakaway configuration and solid-solution impurities located outside of the Suzuki-Cottrell atmosphere, which predicts a squared hysteresis loop and the observed nearly temperature-independent behavior for Q−1H2.