Shuffling mode competition leads to directionally anisotropic mobility of faceted Σ11 boundaries in fcc metals

Abstract

Faceted grain boundaries can migrate in interesting and unexpected ways. For example, faceted Σ11 <110> tilt grain boundaries were observed to exhibit mobility values that could be strongly dependent on the direction of migration. In order to understand whether this directionallyanisotropic mobility is a general phenomenon and to isolate mechanistic explanations for this behavior, molecular dynamics simulations of bicrystals evolved under an artificial driving force are used to study interface migration for a range of boundary plane inclination angles and temperatures in multiple face centered cubic metals (Al, Ni, and Cu). We find that directionallyanisotropic mobility is active in a large fraction of these boundaries in Ni and Cu and should therefore impact the coarsening of polycrystalline materials. On the other hand, no such anisotropy is observed in any of the Al boundaries, showing that this behavior is material-dependent.Migration of the faceted boundaries is accomplished through transformation events at facet nodes and incommensurate boundary plane facets, which are termed shuffling modes. Three major shuffling modes have been identified, namely Shockley shuffling, slip plane shuffling, and disordered shuffling. A shift from the first two ordered modes to the third disordered mode is found to be responsible for reducing or removing directionally-anisotropic mobility, especially at the highest temperatures studied.

Coherent and semicoherent α/β interfaces in titanium: structure, thermodynamics, migration

“…To accommodate the misfit along the α/β interface, b m1 and b m2 glide to follow the interface migration; again retarding interface migration. The similar phenomenon, i.e., stacking fault formation with interface migration in one direction, was also found for tilt grain boundaries in FCC metals 52 . It was suggested that such direction-dependent stacking-fault formation could lead to the directionally anisotropic interface mobility.…”

Emergence of near-boundary segregation zones in face-centered cubic multiprincipal element alloys

“…Cu and Ni are natively FCC, making them good initial candidates for cell generation. A previous study on faceted Σ11 boundaries using six different FCC potentials showed the influence of stacking fault energy on faceted boundary morphology and properties [44]. Between the two elemental choices, pure Cu (from the same interatomic potential) has the closest relaxed stacking fault energy to the reported average for CrFeCoNiCu (50 mJ/m 2 ) and CrFeCoNi (51 mJ/m 2 ).…”

“…These defects, called facet junctions, are interesting in and of themselves as sites with important geometric properties regulating facet structure [38,39], as well as sites of preferred segregation [40]. The faceted Σ11 boundary is of particular interest for having facets with interesting structural features [41][42][43], special defects [42,44], and dynamic behavior [44,45], as well as a well-developed body of literature from chemically simpler materials [10,[41][42][43]46]. Example snapshots of the Σ11 faceted boundary in pure Cu is shown in Fig.…”

A taxonomy of grain boundary migration mechanisms via displacement texture characterization

“…This GB is representative of a poorly understood behavior for twist GBs observed in a recent MD survey [44] in which GBs rigidly slide by a small increment before moving forward. Σ11 GB motion has also recently been analyzed in the context of asymmetric motion in which a specific GB was found to have different mobilities in the forward and backward direction under energy jump driving forces of opposite sign [71,72]. In Section 4.3.2, we explore pattern formation during roughened migration of symmetric tilt GBs upon second yield.…”