Nanopolycrystalline metals and alloys are expected to contribute to new generation engineering structural materials. They have crystallite (grain) sizes in the submicron range, given considerable attention due to their physical and mechanical properties.

They show higher strength and hardness, however, it is important to be able to improve the overall ductility and resistance to fracture. This could be overcome by unique microstructure design.

For this, I am developing a bimodal grain size distribution containing mixed micro- and nanograins in these materials in which the fine grains provide strength and the coarse grains enable strain hardening.

The initial investigation on nanopolycrystalline nickel (Integran Inc, Toronto) showed fascinating and interesting results. The microstructure revealed the abnormally larger grains (two orders of magnitude larger than the fine grains) embedded in fine nanoscale matrix with regular shape.

In future, studying the deformation and fracture resistance in this microstructure will give new dimension to this research. It is also interesting to investigate how different crystal structure materials with different stacking fault energy and grain boundary composition influence the deformation and fracture behaviour.