Dislocation relaxation in cobalt and cadmium polycrystals

Abstract

Abstract The mechanical energy dissipation Q −1 and the resonance frequency f have been measured in specimens of polycrystalline hexagonal cobalt and cadmium, in the temperature range 290K to 90 K during heating and cooling. The specimens were set into flexural vibrations at three different modes having frequencies between 9 and 40 kHz for cobalt, and between 5 and 24 kHz for cadmium. A large thermally-activated relaxation peak was found in both metals at a temperature of 192 K at 17.6 kHz for cobalt and 153 K at 9.8 kHz for cadmium. A subsidiary relaxation peak appeared in both metals at about 100K at the same frequencies. The influence of plastic deformation and high-temperature treatments on the peak height and temperature was also investigated. The main peak was found to possess an activation enthalpy of about 0.25 eV for cobalt and 0.23 eV for cadmium with a limiting characteristic time of the order of 10−12s in both metals. A comparison between the results obtained in cobalt and cadmium with those p...