  Interfacial segregation can stabilize grain structures and even lead to grain
boundary complexion transitions. However, understanding of the complexity of
such phenomena in polycrystalline materials is limited, as most studies focus
on bicrystal geometries. In this work, we investigate interfacial segregation
and subsequent complexion transitions in polycrystalline Cu-Zr alloys using
hybrid Monte Carlo/molecular dynamics simulations. No significant change in the
grain size or structure is observed upon Zr dopant addition to a pure Cu
polycrystal at moderate temperature, where grain boundary segregation is the
dominant behavior. Segregation within the boundary network is inhomogeneous,
with some boundaries having local concentrations that are an order of magnitude
larger than the global value and others having almost no segregation, and
changes to physical parameters such as boundary free volume and energy are
found to correlate with dopant concentration. Further, another alloy sample is
investigated at a higher temperature to probe the occurrence of widespread
transitions in interfacial structure, where a significant fraction of the
originally ordered boundaries transition to amorphous complexions,
demonstrating the coexistence of multiple complexion types, each with their own
distribution of boundary chemical composition. Overall, this work highlights
that interfacial segregation and complexion structure can be diverse in a
polycrystalline network. The findings shown here complement existing
computational and experimental studies of individual interfaces and help pave
the way for unraveling the complexity of interfacial structure in realistic
microstructures.
