Dislocation dynamics in (111)-oriented monocrystalline samples were studied, by means of mechanical spectroscopy, over the temperature range of the flow-stress anomaly. The mechanical loss of specimens which had been pre-deformed at 300K was found to depend strongly upon the temperature, pre-deformation level and heating rate. The loss increased with increasing pre-deformation at 300K, and decreased with increasing temperature. The loss became almost independent of temperature above a transition temperature of about 500K. Thermal cycling and aging experiments provided additional information concerning the annealing-time dependence of mechanical loss, elastic modulus and plastic deformation. The mechanical loss decreased during cycling, while the elastic modulus reflected a clear stiffening effect of the material during cycling. A large twist deformation around the vertical axis was observed when continuous twist excitation was applied, and was attributed to the irreversible glide and/or bowing-out of super-kinks on (111) planes. The results were explained in terms of 2 phenomena which occurred simultaneously as the temperature was increased from 300 to about 500K. These were the exhaustion of mobile dislocation parts (super-kinks), and the pinning of screw dislocation segments by cross-slip from (111) to (010) planes (Kear-Wilsdorf lockings).

Strain-Amplitude Dependent Mechanical Loss at Intermediate Temperatures in a Ni3(Al,Ta) Single Crystal. B.L.Cheng, E.Carreño-Morelli, N.Baluc, J.Bonneville, R.Schaller: Philosophical Magazine A, 1999, 79[9], 2227-42