Investigation on ultrasonic and elastic properties of nano-structured silver by laser ultrasonic method

摘要

The ultrasonic velocities of longitudinal and transverse waves propagating in nano-structured silvers (here after nmAg) are measured by Laser ultrasonic technique. The samples of nmAg are composed of super fine particles with size of 20 to 100 nano-meter (nm). They are prepared by using physical method. An Nd:YAG Q-switched laser with duration 8 ns and adjustable pulse energy from 1 /spl mu/J to 10 m/spl times/ is used as an excitation source. A laser heterodyne interferometer with frequency bandwidth of 18 MHz, a PVDF transducer with a frequency bandwidth of 125 MHz, and a LiNbO/sub 3/ transducer with a center frequency 7.5 MHz are used as the receivers. The experimental results show that the velocities and attenuation of nmAg depend on their grain size, porosity and annealing conditions as well as on the ultrasonic frequency, which are different with those of conventional Ag. The elastic modules of nmAg are deduced. The relation between the experimental results and the conditions of samples are analyzed. The comparisons with that of conventional Ag are given.