Molecular Dynamics Study of Mechanical Properties and Inelastic Deformation Mechanism of Nanocrystalline Materials under Tensile Loading.

Abstract

Nano-polycrystalline material that consists of many minute (nanometer order) grains shows some interesting mechanical properties;e.g.opposite Hall-Petch relationship, superplasticity, and elastic modulus softening. To clarify the origin of these properties, we study the behavior of 3-dimensional nano-polycrystalline model under uniaxial tensile loading. The model consists of 48 aluminum grains and the dynamics of total 551011 atoms are simulated by using a large scale parallel molecular dynamics (MD). First, it is shown that the elastic moduli is located on intermediate value between the overall properties estimated by Voigt and Reuss models. Then, it is shown that crystalline slips caused by dislocations emitted from grain boundaries are one of main mechanisms of its deformation. Finally, the technique of the stereographic projection which is used to investigate the rotation of each grains in usual polycrystalline material, is applied to this atomistic simulation to elucidate a mechanism of slip. As the result, it is concluded that the crystal slip and grain rotation which are often observed in usual polycrystalline material appear during the atomistic deformation and they play an important role of the mechanism of inelastic deformation in nano-polycrystalline material.