  Segregation-induced structural transitions in metallic grain boundaries are
studied with hybrid atomistic Monte Carlo/molecular dynamics simulations using
Cu-Zr as a model system, with a specific emphasis on understanding the effect
of grain boundary character. With increasing global composition, the six grain
boundary types chosen for this study first form ordered complexions, with the
local segregation pattern depending on the grain boundary core structure, then
transform into disordered complexions when the grain boundary composition
reaches a critical value that is temperature dependent. The tendency for this
transition to a disordered interfacial structure consistently depends on the
relative solute excess, instead of the grain boundary energy or misorientation
angle. Grain boundaries with high relative solute excess go through gradual
disordering transitions, whereas those with low relative solute excess remain
ordered until high global Zr concentrations but then abruptly transform into
thick disordered films. The results presented here provide a clear picture of
the effect of interface character on both dopant segregation patterns and
disordered intergranular film formation, showing that all grain boundaries are
not equal when discussing complexion transitions.
