Strain localization in a nanocrystalline metal: Atomic mechanisms and the effect of testing conditions

Abstract

Abstract:Molecular dynamics simulations are used to investigate strain localization in a model nanocrystalline metal. The atomic mechanisms of such catastrophic failure are first studied for two grain sizes of interest. Detailed analysis shows that the formation of a strain path across the sample width is crucial, and can be achieved entirely through grain boundary deformation or through a combination of grain boundary sliding and grain boundary dislocation emission.Pronounced mechanically-induced grain growth is also found within the strain localization region. The effects of testing conditions on strain localization are also highlighted, to understand the conditions that promote shear banding and compare these observations to metallic glass behavior. We observed that, while strain localization occurs at low temperatures and slow strain rates, a shift to more uniform plastic flow is observed when either strain rate or temperature is increased. We also explore how external sample dimensions influence strain localization, but find no size effect for the grain sizes and samples sizes studied here.2

From metallic glasses to nanocrystals: Molecular dynamics simulations on the crossover from glass-like to grain-boundary-mediated deformation behaviour

“…The possibility of purely grain-boundary-mediated deformation has been reported before for Ni [67], where it is enabled by a free percolation path for shear bands through the sample. Our results furthermore indicate that the participation of the crystalline phase in the deformation also depends on the intrinsic proclivity towards strain localisation in the amorphous phase.…”

Fabrication of 3D Micro-Architected/Nano-Architected Materials

“…(13.1.3) predicts enormous strengthening as the grain size is reduced to the atomic scale (and the microstructure becomes amorphous); in practice, once the grain size goes below ∼10 nm, plasticity becomes controlled by other mechanisms (primarily grain boundary sliding [53] and shear banding [54]). Eq.…”

The ultra-small strongest grain size in nanocrystalline Ni nanowires

“…It is also found that the transition in plastic deformation mechanisms in metals strongly depends on temperature. For example, Hughes and Hansen [9] have revealed that at low temperatures, the dislocation-based plasticity in nanostructured metals may exist far below the transition suggested by previous experiments and molecular dynamics (MD) simulations, with a limit of <5 nm.On the other hand, one-dimensional metal nanostructures such as nanowires (NWs) and nanopillars have attracted significant attention in recent years due to their unique mechanical properties [10][11][12][13][14][15][16][17]. As compared to bulk nanocrystalline metals, the plasticity in metal NWs and nanopillars is more complicated due to the possible contribution from the external free surfaces [14].…”

“…On the other hand, one-dimensional metal nanostructures such as nanowires (NWs) and nanopillars have attracted significant attention in recent years due to their unique mechanical properties [10][11][12][13][14][15][16][17]. As compared to bulk nanocrystalline metals, the plasticity in metal NWs and nanopillars is more complicated due to the possible contribution from the external free surfaces [14].…”

“…Here the flow stress (r F ) in Figure 3e was calculated using the average of the tensile stress between 6% and 10% tensile strain as similar to that used for nanocrystalline bulk metals [5], whereas the yield stress was extracted based on 1% offset (r y ) [15]. It is found in Figure 3d and e that while the flow stress (r F ) and yield stress (r y ) both monotonically increase with decreasing temperature, they each show a distinct dependence on the grain size.…”