Mechanically driven grain boundary relaxation: a mechanism for cyclic hardening in nanocrystalline Ni

Abstract

Molecular dynamics simulations are used to show that cyclic mechanical loading can relax the non-equilibrium grain boundary (GB) structures of nanocrystalline metals by dissipating energy and reducing the average atomic energy of the system, leading to higher strengths. The GB processes that dominate deformation in these materials allow low-energy boundary configurations to be found through kinematically irreversible structural changes during cycling, which increases the subsequent resistance to plastic deformation.

Keywords:

• nanocrystalline materials
• mechanical properties
• grain boundary relaxation
• molecular dynamics
• plastic deformation

Acknowledgements

This study was supported by the US Army Research Office, through grant W911NF-09-1-0422 and through the Institute for Soldier Nanotechnologies at MIT.