ELASTIC AND DISSIPATIVE PROPERTIES OF METALS WITH AN ULTRAFINE GRAIN-STRUCTURE

The sound wave velocity and internal friction were measured in samples of nanocrystalline silver and submicrocrystalline copper as functions of annealing temperatures by several acoustic techniques operating at different frequencies. It was found that at room temperature in the a s-prepared samples the modulus defect is extremely large (up to 20%) a nd disappears only after annealing at temperatures above that of prima ry recrystallization. The effect does not depend on frequency. In-situ measurements demonstrated an internal friction peak and corresponding modulus change at the temperature of primary recrystallization. The s uggestion is made that the observed anelastic behaviour is caused by s tructural rearrangement in the grain boundary region.