Shear responses of $[\bar{1}\,1\,0]$ -tilt {1 1 5}/{1 1 1} asymmetric tilt grain boundaries in fcc metals by atomistic simulations

Abstract

The shear response of the 3 [1 1 0]-tilt (11 5)/(1 1 1) and 9 [1 1 0]-tilt (1 1 5)/(1 1 1) asymmetric tilt grain boundaries (GBs) in fcc metals Cu and Al has been studied by atomistic simulation methods with the embedded atom method interatomic potentials and with a bicrystal model. It is found that the structure of the GBs studied can be well described by the coincidence site lattice (CSL) theory. Shear of these GBs at room temperature along eight different directions within the GB plane shows that these two types of GBs can transform between each other by the formation of a coherent twin boundary. The structure transformation of the GBs can also take the form of GB sliding, GB sliding-migration coupled motion, GB faceting, GB 9R structure formation, etc, depending on the shear directions adopted and the material involved (Cu or Al). The detailed structure transformation mechanisms have been analyzed with the aid of the CSL-DSC (displacement shift complete) theory. Several structure transformation paths adherent to these two types of GBs have been identified for the activation of the GB sliding-migration coupled motion. It is concluded that, although CSL-DSC theory can be applied to describe the sliding-migration coupled motion of the GBs studied, some other effects such as the shear direction within the GB plane and the bonding characteristics of the materials should also play a significant role in the shear response of these GBs.

Dislocation Nucleation on Grain Boundaries: Low Angle Twist and Asymmetric Tilt Boundaries

“…Nucleation of such dislocation requires nucleation of additional defects at the GB, as observed previously [24]. Plasticity of asymmetric tilt boundaries is clearly a complex problem featuring multiple competing deformation mechanisms [10,[22][23][24]. The unifying mathematical description of such boundaries is still an open problem.…”

“…In the present study, we find that a nucleation mechanism deformation and combination of the existing GB dislocations produces lattice dislocations. Inelastic deformation of asymmetric tilt boundaries is known to occur by several distinct mechanisms: GB sliding by uncorrelated atomic shuffling [10] similar to the intermittent flipping mechanism in granular materials [21], nucleation of lattice dislocations [10,22], GB migration [10,23,24], faceting [23], and motion of a mobile GB dislocation [24]. Here, we find that the nucleation of GB dislocation occurs only for a dense GB (low excess volume) and that it is accompanied by nucleation of lattice partials which create short stacking faults adjacent to the boundary.…”

Atomistic modeling of different loading paths in single crystal copper and aluminum

“…Therefore, an important ingredient for successful theory is to take into account whole range of important properties heavily influenced by atomic distribution symmetries in space coordinates. They are associated with the crystallography of the grains and the structure of grain boundaries [8]. Fig.…”

“…There has been substantial progress in modeling nucleation and growth of fatigue cracks under multiaxial stresses like Fatemi-Socie [6] parameter applied to steel specimens. However, at the fundamental atomic scale it turns out that the full resolved stresses play also very important role [7,8].…”

Atomistic modeling study of a strain-free stress driven grain boundary migration mechanism

“…Migration of the B/P boundary in this case is accomplished via a 'unit-cell-reconstruction' mechanism [15], and it produces a tetragonal strain by the migration of the boundary [14]. For both the shear coupled GB migration and the migration of the B/P boundary in Mg, atomic shuffling motions in the GB zone can be identified as a complementary process on migration of the GB [14,16,17]. In short, the stress driven GB migration is generally characterized by a transformational strain produced in the volume swept by the motion of GB together with complementary atomic shuffling motions in the volume.…”