Grain growth and deformation in nanocrystalline materials

In case of nanocrystalline materials several additional features need to be taken into account in considering grain growth and deformation whose existence was first anticipated by Professor J.C.M. Li years ago. Grains can increase their size by grain rotation as well as by curvature driven motion. Grain rotation has been considered in detail by Li [J.C.M. Li, J. Appl. Phys. 15 (1962) 2958] theoretically and recently other researchers by simulation. We show that in nanocrystalline materials this mode is quite possible especially if the grain growth is retarded by finite triple junction mobility. New deformation modes occur in these materials leading to the so-called inverse Hall-Petch effect, which will be discussed in detail.