THEORY OF LOW-FREQUENCY NONLINEAR ANELASTIC INTERNAL-FRICTION PEAKS AROUND ROOM-TEMPERATURE

Since a low-frequency internal friction phenomenon exhibiting anomalou s amplitude effect was observed in an Al-Cu alloy [1], a series of sim ilar internal friction peaks versus temperature were observed in cold- worked and partially annealed AI-Mg and Al-Cu dilute alloys [2]. These internal friction peaks exhibit the common features of relaxation cha racteristics and anomalous amplitude effects giving rise to internal f riction peaks versus strain amplitude in the temperature range of the internal friction peaks versus temperature. This series of nonlinear a nelastic internal friction peaks were considered to be originated from the dislocation slip or kink drift, rate-controlled by different diff usion processes of different point defects interacting with dislocatio ns 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 di slocations or kinks. An attempt is made to establish a simple interact ion model between kinks and point defects using a low-frequency approx imation and to demonstrate at least semiquantitatively how the interac tion between dislocations and mobile point defects can give rise to an elastic relaxation peaks with anomalous amplitude effect. The theoreti cal results obtained correspond satisfactorily with the experimentally observed internal friction phenomena (e.g. P-1'' peak) around room te mperature in AI-Mg and AI-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.