The reduction of the grain size to the nanometer range has led to many interesting material properties, including those involving structural and mechanical behaviour. Basic assumptions of dislocation theory may no longer be appropriate in nanocrystalline metals and new mechanisms that may come into play at these very small dimensions need to be explored and studied.
Large-scale molecular dynamics simulations of structural and mechanical properties of nanocrystalline Ni samples do provide intriguing insights into the effects of grain size and grain boundary (GB) structure. The simulations suggest a deformation mechanism intrinsic to the nanosized GB network where the GB structure plays a central role consisting of an interplay between (1) GB sliding accommodated by GB and Triple Junction migration and (2) dislocation emission and absorption in GBs, both at the origin of the formation of local shear planes that facilitates plastic deformation. The proposed mechanisms are interpreted in terms of experimental results such as work hardening and characteristic features on the fracture surface.
The synergies provided by molecular dynamics computer simulations and classical experimental investigations have resulted in the development of a very successful new experimental approach: in-situ profile analysis at the Swiss Light Source.
Hasnaoui, A., Van Swygenhoven, H. & Derlet, P. M, Science 2003
Van Swygenhoven, H. & Derlet, P. M, Phys. Rev. B 64, 224105-9 (2001)
Van Swygenhoven, H., Derlet, P. M. & Hasnaoui, Phys. Rev. B 66, 024101-8 (2002).