ACOUSTICAL CHARACTERIZATION OF NANOSTRUCTURED METAL

Abstract

Ultrasonic attenuation due to phonon–phonon interaction, thermoelastic loss and dislocation damping arising from screw and edge dislocations has been evaluated in nanocrystalline copper (13 nm) in the temperature range 50–500 K, and size-dependent attenuation at a constant temperature for longitudinal and shear modes of propagation. Second and third order elastic constants have been obtained, taking the nearest neighbor distance and the hardness parameter as input data. SOEC and TOEC (obtained at different temperatures) have been used to obtain Grüneisen parameters and nonlinearity parameters, which in turn have been used to evaluate α/f2 for longitudinal and shear waves. Results have been discussed, and compared with available experimental values. It has been found that α/f2 increases with temperature and a significant contribution to the total attenuation occurs due to scattering from grain boundaries, and ultrasonic attenuation due to thermoelastic loss is negligible compared to phonon–phonon interaction, establishing that the major part of energy from the sound wave is removed owing to the interaction of acoustic phonons with thermal phonons (lattice vibrations).