Stability and relaxation mechanisms of a wedge disclination in an HCP bicrystalline nanowire

摘要

The concept of critical disclination strength (omega(c)) in HCP bicrystalline nanowires is developed on the basis of atomistic simulations using the modified embedded atom method. Disclinated titanium nanowires are created atomistically by combining two bicrystals with different misorientations along the [1 (1) over bar 00] tilt axis. Relaxations via molecular dynamic simulations of the atomic configurations at zero temperature result in either a stable or an unstable disclination, giving rise to the concept of omega(c). An empirical size effect law for omega(c) is developed for nanowires with diameters between 10 and 20 nm, and extrapolation of this law to larger diameters yields predictions consistent with experimental data for plastically deformed titanium. As the disclination strength increases beyond omega(c), various relaxation mechanisms are predicted depending on the grain boundary structures. For disclinations created by inserting a bicrystal into a reference one with B. B grain boundary structures, the three predicted relaxation mechanisms are basal plane and grain boundary cleavage, basal plane and grain boundary cleavage as well as new HCP grain nucleation ahead of the grain boundary crack and prismatic plane and grain boundary cleavage.