Growth and structural transitions of core-shell nanorods in nanocrystalline Al-Ni-Y

TL;DR

This study investigates the formation, structure, and evolution of core-shell nanorods in nanocrystalline Al-Ni-Y alloys, revealing their role in stabilization and strengthening during annealing.

Contribution

It provides detailed insights into the nucleation, chemical composition, and structural transitions of nanorods in Al-Ni-Y alloys, highlighting the influence of annealing on their properties.

Findings

Nanorods nucleate at grain boundaries with core-shell structures.

Annealing induces ordering and coarsening of nanorods.

Shell chemistry shifts from Y-rich to Ni-rich with annealing.

Abstract

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.