Molecular Dynamics Study of Structure and Mechanical Properties of Grain Boundaries in Nanocrystalline Materials.

Abstract

Grain boundary (GB) structures of Al nanopolycrystalline (NPC) materials and their mechanical properties are studied by using molecular dynamics simulation. An embedded atom method (Mishin et al. 1999) is adopted to describe the interatomic interaction. First, bicrystal models are studied to evaluate the GB energies, then three different NPC models are examined to investigate the dependency of grain size, and a computational tensile test of a NPC model is carried out. In the bicrystal simulation, the result is compared with the effective medium theory, experiment and abinitio calculation and it corresponds well with them. Concerning NPC models, the atoms located in GBs are distinguished and the average site potential energy and the average specific volume over the atoms in GBs are calculated. The relation between these values and misorientation angles shows that there is a structural difference between low angle and high angle GBs and the border is about 20 degree. In the simulation of tensile test, the result shows the GB sliding is closely related to not only Schmid factor of inclination of GB plane but the GB character, i.e. it is observed at high-energy and low-density GB. Migrations of low angle GB that is not necessarily easy in coarse-grain polycrystals, are often observed. It is concluded that the mechanical properties and deformation mechanisms of NPC materials are closely related to the microscopic GB character and that the computer simulation play an important role as an indispensable tool to estimate GB character and to design the NPC materials.