  Unique nanorod precipitates with a core-shell structure are found to nucleate
from the grain boundaries of a bulk nanocrystalline Al-Ni-Y alloy fabricated
via powder consolidation, contributing significantly to stabilization and
strengthening. The local structure, chemistry, and evolution of these features
during annealing is reported here. In the as-consolidated state, the nanorods
can be either structurally ordered or disordered, yet a consistent chemical
patterning is found where the core is primarily Al plus C while the shell is
enriched with Y. As annealing time increases, more nanorods transform to an
ordered structure as they coarsen while the core composition remains unchanged.
In contrast, the shell chemistry transitions from Y-rich to Ni-rich with longer
annealing treatments, most likely due to the different diffusivities of Y and
Ni in Al. Moreover, a spatial and chemical correlation between the nanorods and
amorphous complexions is observed, suggesting that these complexions serve as
preferential nucleation sites.
