Theory of Low-Frequency Nonlinear Anelastic Internal Friction Peaks around Room Temperature

Abstract

Since a low-frequency internal friction phenomenon exhibiting anomalous amplitude effect was observed in an Al-Cu alloy [1], a series of similar internal friction peaks versus temperature were observed in cold-worked and partially annealed Al-Mg and Al-Cu dilute alloys [2]. These internal friction peaks exhibit the common features of relaxation characteristics and anomalous amplitude effects giving rise to internal friction peaks versus strain amplitude in the temperature range of the internal friction peaks versus temperature. This series of nonlinear anelastic internal friction peaks were considered to be originated from the dislocation slip or kink drift, rate-controlled by different diffusion processes of different point defects interacting with dislocations or kinks. The amplitude effect can be ascribed to the dependence of the mobility of the dislocations or kinks on the amplitude because of the escaping of point defects from the stress fields of the moving dislocations or kinks. An attempt is made to establish a simple interaction model between kinks and point defects using a low-frequency approximation and to demonstrate at least semiquantitatively how the interaction between dislocations and mobile point defects can give rise to anelastic relaxation peaks with anomalous amplitude effect. The theoretical results obtained correspond satisfactorily with the experimentally observed internal friction phenomena (e.g. P 1 peak) around room temperature in Al-Mg and Al-Cu alloys. This P 1 peak was considered to be related to the transverse core diffusion (TCD) of the solute atoms within the dislocation core.