  Stabilization of grain structure is important for nanocrystalline alloys, and
grain boundary segregation is a common approach to restrict coarsening. Doping
can alter grain boundary structure, with high temperature states such as
amorphous complexions being particularly promising for stabilization. Dopant
enrichment at grain boundaries may also result in precipitate formation, giving
rise to dopant partitioning between these two types of features. The present
study elucidates the effect of dopant choice on the retention of amorphous
complexions and the stabilization of grain size due to various forms of
interfacial segregation in three binary nanocrystalline Al-rich systems, Al-Mg,
Al-Ni, and Al-Y as investigated in detail using transmission electron
microscopy. Amorphous complexions were retained in Al-Y even for very slow
cooling conditions, suggesting that Y is the most efficient complexion
stabilizer. Moreover, this system exhibited the highest number density of
nanorod precipitates, reinforcing a recently observed correlation between
amorphous complexions and grain boundary precipitation events. The dopant
concentration at the grain boundaries in Al-Y is lower than in the other two
systems, although enrichment compared to the matrix is similar, while secondary
segregation to nanorod precipitate edges is much stronger in Al-Y than in Al-Mg
and Al-Ni. Y is generally observed to be an efficient doping additive, as it
stabilizes amorphous features and nanorod precipitates, and leaves very few
atoms trapped in the matrix. As a result, all grains in Al-Y remained nanosized
whereas abnormal grain growth occurred in the Al-Mg and Al-Ni alloys. The
present study demonstrates nanocrystalline stability via simple alloy
formulations and fewer dopant elements, which further encourage the usage of
bulk nanostructured materials.
