Grain-size dependence of the relationship between intergranular and intragranular deformation of nanocrystalline Al by molecular dynamics simulations

Abstract

The strength of nanocrystalline aluminum has been studied using molecular dynamics simulation. Nanocrystalline models consisting of hexagonal grains with grain size d between 5 nm and 80 nm are deformed by the application of tension. A transition from grain-size hardening to grain-size softening can be observed in the region where d Ϸ 30 nm, which is the optimum grain size for strength. In the grain-size hardening region, nanocrystalline models primarily deform by intragranular deformation. Consequently, a pile-up of dislocations can be observed. When the grain size becomes less than 30 nm, where the thickness of the grain boundaries cannot be neglected in comparison to the grain sizes, the dominant deformation mechanism of nanocrystalline metals is intergranular deformation by grain boundary sliding. Further, geometrical misfits by grain boundary sliding are accommodated by the grain rotation mechanism. Moreover, cooperative grain boundary sliding occurs in the 5 nm model. The optimum grain size is controlled by the relationship between resistance to intergranular deformation by grain boundary processes and intragranular deformation resisted by the grain boundary. Therefore, the primary role of the grain boundary changes in the region where the optimum grain size is observed.

Local Atomic Configuration of Dislocation-Accumulated Grain Boundary and Energetics of Gradual Transition from Low Angle to High Angle Grain Boundary in Pure Aluminum by First-Principles Calculations

“…In addition, inverse relationship to Hall-Petch relation is predicted and it is elucidated by transition from dislocation-driven deformation to grain boundary-driven deformation. [14][15][16] These rather peculiar properties, in contrast to conventional materials properties, can be attributed to much finer grain size of UFG than in conventional materials. Furthermore, it is easily expected that UFG materials would acquire new properties other than mechanical properties including transport properties of electron, heat, or atoms, since increased number of GBs modify the transport along or across the GBs.…”

“…We chose Al, a typical fcc metal, as a model material since Al is one of the most extensively studied SPDed materials both experimentally and computationally. 1,2,6,16,20,21,[27][28][29][30][31][32][33][34] This paper is composed as follows: After explaining computational details in the next section, dependence of GB excess energy on microscopic structural parameter of GB is quantified and relationship between dislocations and GBs is discussed. It is followed by quantification of interaction energy between dislocations at GB and deviation from theory of elasticity is discussed.…”

Atomistic simulation study of the shear-band deformation mechanism in Mg-Cu metallic glasses

“…This designation is maintained throughout the deformation, and in visualizing any later configuration, only the black atoms are shown. A similar method was used recently by Shimokawa et al 28 Figure 5 shows how the initial straight, parallel stripes become stretched as the deformation proceeds. It is clear that most of the deformation takes place in two bands that lead away from the notch at 45°, while little deformation takes place in the remaining material.…”

Effects of Vacancies on Deformation Behavior in Nanocrystalline Nickel

“…Atomic and dislocation events taking place during deformation can be monitored by MD simulation with a 2D columnar cell unit, [26][27][28][29] although there is a difference in the level of dislocation activity between 2D columnar and 3D nanocrystalline structures. 30) MD simulation with a 2D columnar cell unit permits the investigation of specimens much larger grain sizes and with a constant microstructure.…”