Interfaces play a decisive role in the deformation of any polycrystalline metal or precipitate-strengthened alloy. Perhaps best known is the role of grain boundaries (GBs) as obstacle to dislocation motion as evidenced by the Hall-Petch strengthening. However, GBs can also serve as initiation sites for fracture and provide easy pathways for crack propagation. When the grain size is reduced below 100 nm, GBs become furthermore the dominant sources and sinks for dislocations, and pinning of dislocations at GBs becomes an important hardening mechanism. At very small grain sizes below about 10 nm, the contribution of grain boundary glide and grain rotation becomes significant. All these processes take place at the atomic scale. Consequently, atomistic simulations have played a key role in studying grain- and interphase boundaries (IPBs), and their interactions with dislocations. However, most of the detailed studies on dislocation – interface interactions were performed on quasi-two dimensional simulation setups with straight dislocation lines interacting with perfectly planar interfaces. Similarly, the deformation of nanocrystalline metals is commonly studied using artificial structures generated by means of the Voronoi tessellation. This procedure creates planar GBs and non-equilibrium triple junction topologies, as well as unrealistic numbers of neighboring grains and distributions of triple line lengths.
Here we give an overview on our recent atomistic studies on dislocation – interface interactions, with the focus on non-planar boundaries and more realistic GB topologies. Simulations on twinned nanoparticles and nanowires are used to demonstrate that the presence of twin boundaries can change the deformation mechanism, thereby explaining experimentally observed dislocation structures. Controlled studies on dislocations interacting with various high-angle GBs in a bicrystal setup allow to quantify changes in the stress field and energy of absorbed dislocations and show the importance of GB curvature on slip transmission through GBs. We then compare the processes taking place in various nanocrystalline samples with different degrees of GB curvature as well as different GB network topologies. Here, a statistical analysis shows clear differences in terms of stress states and contributions of dislocation glide versus GB-mediated processes, however the distribution of critical stresses for dislocation nucleation and dislocation depinning from GB as well as on the distribution of plastic strain caused by individual slip events remains unaffected by the GB topology. Finally, we report on simulations on atom probe tomography – informed superalloy samples, which reveal the importance of interface curvature and chemical composition on the misfit dislocation network and subsequent interactions with matrix dislocations.