Abstract
When grain size decreases to the nanometer scale, dislocation structures hardly form in the grain; hence, it cannot be expected to obtain a large work hardening rate for nanostructured materials within the conventional framework of the theory based on the dislocation-dislocation interaction. However, the strength controlling mechanism of nanostructured materials could be different from that of coarse-grained materials; dislocation emission from grain boundaries must control the strength of nanostructured materials because of a shortage of intragranular dislocation sources. Therefore, if the resistance to following dislocation emissions from a site of grain boundaries can increase after the first dislocation emission from the site, we can expect that nanostructured materials can show large ductility due to the grain-boundary dislocation source hardening mechanism. In this paper, we first show the possibility of the grain-boundary dislocation source hardening mechanism to various Al <112> tilt grain boundaries and then consider the effect of the grain-boundary dislocation source hardening mechanism on ductility of nanostructured materials by performing tensile loading tests of nano-sized round-bar specimens.
