Anatomy of nanomaterial deformation: Grain boundary sliding,plasticity and cavitation in nanocrystalline Ni

The deformation of nanocrystalline metals is a complex process that involves a cascade of plastic events, including dislocation motion, grain boundary activity and cavitation. These mechanisms act simultaneously and synergistically during fracture, masking their individual roles and often resulting in a wide range of failure modes in the same material. Using large-scale molecular dynamics simulations, we dissect the size-dependent deformation of nanocrystalline Ni nanowires for a range of diameters spanning a few nanometers to the bulk. By analyzing the localization of von Mises shear strain and stress triaxiality, we identify the key nanostructural features, the role of each elementary process and the dominant deformation mechanism as a function of sample diameter. Our atomic level analysis not only provides a fundamental understanding of the deformation of nanocrystalline Ni, but also demonstrates that large-scale simulations can be an essential complement for modern in situ electron microscopy/atom-probe tomography.