  Grain boundary-based mechanisms are known to control the plastic deformation
and failure of nanocrystalline metals, with manipulation of the boundary
structure a promising path for tuning this response. In this study, the role of
interfacial structural disorder on plasticity and failure of nanocrystalline
Cu-Zr alloys is investigated with in situ scanning electron microscopy tensile
deformation experiments. Two model materials are created, one with only the
typical ordered grain boundaries and another with amorphous intergranular films
interspersed into the boundary network, while the microstructures are otherwise
identical. Hence, the importance of complexion type on plasticity and failure
is isolated by only varying complexion structure. The tensile experiments show
that failure of the samples containing amorphous films is significantly
retarded, as evidenced by an increase in the cross-sectional area reduction, a
decrease in the occurrence of shear-dominated failure, a decrease in strain
localization, and fracture surfaces with more elongated dimple features. As a
whole, this study provides direct evidence that structural disorder at the
grain boundaries can be beneficial for improving the ductility of
nanocrystalline metals.
