Intrinsic Bauschinger Effect and Recoverable Plasticity in Pentatwinned Silver Nanowires Tested in Tension

Silver nanowires are promising components
of flexible electronics
such as interconnects and touch displays. Despite the expected cyclic
loading in these applications, characterization of the cyclic mechanical
behavior of chemically synthesized high-quality nanowires has not
been reported. Here, we combine in situ TEM tensile tests and atomistic
simulations to characterize the cyclic stress–strain behavior
and plasticity mechanisms of pentatwinned silver nanowires with diameters
thinner than 120 nm. The experimental measurements were enabled by
a novel system allowing displacement-controlled tensile testing of
nanowires, which also affords higher resolution for capturing stress–strain
curves. We observe the Bauschinger effect, that is, asymmetric plastic
flow, and partial recovery of the plastic deformation upon unloading.
TEM observations and atomistic simulations reveal that these processes
occur due to the pentatwinned structure and emerge from reversible
dislocation activity. While the incipient plastic mechanism through
the nucleation of stacking fault decahedrons (SFDs) is fully reversible,
plasticity becomes only partially reversible as intersecting SFDs
lead to dislocation reactions and entanglements. The observed plastic
recovery is expected to have implications to the fatigue life and
the application of silver nanowires to flexible electronics.