  The ability of amorphous intergranular films to mitigate damage formation at
grain boundaries is studied with molecular dynamics simulations. We find that
such films can alter both crack nucleation and crack growth rates by
efficiently absorbing dislocations, with thicker films being more effective
sinks. Local plastic strain brought by incoming dislocations is diffused into a
triangular region within the amorphous film and is accommodated by a flow of
boundary atoms which resembles a vortex shape; this vortex grows inside of the
amorphous intergranular film as more dislocations are absorbed until it reaches
the opposite amorphous-crystalline interface, after which cracks can finally be
nucleated. Even after nucleation, these cracks grow more sluggishly in an
amorphous intergranular film than they do along a clean grain boundary, since
the driving force for crack growth is lower in the amorphous film. The results
presented here suggest that amorphous intergranular films can act as toughening
features within a microstructure, and thus are promising for designing
nanostructured materials with better ductility and fracture toughness.
