The elastic properties of nanostructured Ag measured by laser ultrasonic technique

The elastic properties of nanostructured Ag (ns-Ag) and its changing behavior during densification and annealing were investigated by a laser ultrasonic technique. The ns-Ag with grain size d about 30 nm was synthesized by inert gas condensation and in-situ compaction. The experimental results indicate that the Poisson's ratio, and the shear as well as the Young's modulus for all ns-Ag specimens investigated are smaller than the corresponding values for polycrystalline Ag (p-Ag). It was found that the change of the Poisson's ratio with the density is non-monotonic. It decreases with decreasing density as the relative density is higher than similar to 93%, below which it increases with decreasing density. We found that the increase of elastic modulus with density is nonlinear. It exhibits three-stage behavior. (i) a rapid descent stage, when the relative density D< similar to 93%; (ii) a relatively stable stage (93%<D<95%), and (iii) a rapid ascent stage (D>95%). In addition,for annealed specimens, the modulus decreases with increasing annealing temperature. It is similar to the density change during annealing, while the variation of the Poisson's ratio resembles more the changing behavior of the grain size of ns-Ag. All these results were discussed based on the microstructural characteristics of ns-Ag. (C) 1998 Acta Metallurgica Inc.