Multiscale modelling of dislocation/grain-boundary interactions: I. Edge dislocations impinging on Σ11 (1 1 3) tilt boundary in Al

Abstract

Dislocation and grain-boundary processes contribute significantly to plastic behaviour in polycrystalline metals, but a full understanding of the interaction between these processes and their influence on plastic response has yet to be achieved. The coupled atomistic discrete-dislocation method is used to study edge dislocation pile-ups interacting with a Σ11-⟨1 1 3⟩ symmetric tilt boundary in Al at zero temperature under various loading conditions. Nucleation of grain-boundary dislocations (GBDs) at the dislocation/grain-boundary intersection is the dominant mechanism of deformation. Dislocation pile-ups modify both the stress state and the residual defects at the intersection, the latter due to multiple dislocation absorption into the boundary, and so change the local grain-boundary/dislocation interaction phenomena as compared with cases with a single dislocation. The deformation is irreversible upon unloading and reverse loading if multiple lattice dislocations absorb into the boundary and damage in the form of microvoids and loss of crystalline structure accumulates around the intersection. Based on these results, the criteria for dislocation transmission formulated by Lee, Robertson and Birnbaum are extended to include the influences of grain-boundary normal stress, shear stress on the leading pile-up dislocation and minimization of step height at the intersection. Two possible yield loci for the onset of GBD nucleation versus compressive stress and relevant shear stresses are derived from the simulations. These results, and similar studies on other boundaries and dislocation characters, guide the formulation of continuum constitutive behaviours for use in discrete-dislocation or strain-gradient plasticity modelling.

Interfacial plasticity governs strain rate sensitivity and ductility in nanostructured metals

“…The real situation is much more complex, however. Instead of the present arrangement, where the Burgers vector lies in the TB plane, the incoming and outgoing dislocations may carry a net Burgers vector with out-of-plane components (18,20,21) and also leave behind residual dislocations on the TB after transmission. We therefore expect a 2D interfacial dislocation network to develop on the TB during general deformation, in which case both int and the J-f luxes should be tensorial quantities (35) instead of scalars.…”

“…To model ductility, it is necessary to revisit detailed physical processes at materials interfaces, in particular those involving dislocations, which are the carriers of plastic strain. Dislocation processes at internal interfaces usually involve slip transfer from one inelastic shear system to another (18)(19)(20)(21). Various experimental observations, including highresolution transmission electron microscopy, indicate that the involvement of bulk dislocations is indispensable for the plastic deformation of most nanocrystalline metals at low temperatures (13).…”

Molecular-dynamics simulations of stacking-fault-induced dislocation annihilation in prestrained ultrathin single-crystalline copper films

“…The reported mechanisms of dislocation depletion, however, are not artificially induced due to the high initial dislocation density since these mechanisms are similar to those identified in recent studies of dislocation interactions with twin boundaries in samples with lower dislocation densities. [41][42][43][44] Finally, the initially deformed ͑pre-strained͒ structures preceding the dynamical loading are not stress free after the thermal equilibration procedure. The resulting residual elastic strain in our thin films at the beginning of the dynamic deformation simulations represents more realistically the residual strains in the metallic thin films in complex and heterogeneous device structures.…”

“…[41][42][43][44] Particularly, twin-boundarymediated dislocation dissociation reactions ͑also termed slip transfer reactions͒ were shown to be the rate controlling mechanisms of plastic flow in nanotwinned materials and their high ductility was attributed to the structural evolution caused by such mechanisms. 44 These twin-mediated mechanisms are similar to those in categories I and II in our analysis; for the twin-mediated mechanisms similar to those in categories I͑a͒ and II, the activation barrier was reported to be ϳ0.49 eV, whereas for mechanisms similar to those in category I͑b͒, it was reported to be ϳ0.67 eV.…”

Review on slip transmission criteria in experiments and crystal plasticity models

“…Thus, the residual Burgers vector vanishes for an ideal transmission event, where both slip directions, i.e., also the Burgers vectors for both slip systems, are coinciding. The three criteria of a geometric transmission factor combined with RSS and RBV have been investigated experimentally and computationally, mainly for face-centered cubic (FCC) crystal structured materials, e.g., [33][34][35][36][37][38][39] and often for symmetric grain boundaries [40][41][42][43][44] (see [36] for an overview of investigations on FCC including a list of boundary types). However, more recent works also consider general grain boundaries [35,45].…”