Effect of Pressure on Dislocation Damping in Aluminum Crystals

Abstract

Attenuation of megahertz ultrasound has been measured in an aluminum crystal under hydrostatic pressure at room temperature. From the pressure dependence of attenuation at various sound frequencies, the pressure dependence of damping constant for dislocation motion was determined by an analysis based on the overdamped resonance theory of dislocation. Specimen used was primarily zone-refined 99.9999% Al single crystal containing 1 ppm of Si as impurities. The specimen was irradiated by neutrons and 2–4 ppm of Si atoms were further introduced by a nuclear reaction. The specimen was also heat-treated in various ways. Thus the amount and state of impurity atoms were altered, and the high pressure experiments were made for the specimen in different states. The pressure dependence of damping constant was found to be very sensitive to the state of impurities. The order of magnitude and even the sign of the dependence were different for different impurity states. A qualitative discussion was given to interpret the experimental results.