  Amorphous complexions in nanocrystalline metals have the potential to improve
mechanical properties and radiation tolerance, as well as resistance to grain
growth. In this study, the stability of amorphous complexions in binary and
ternary Cu-based alloys is investigated by observing the effect of cooling rate
from high temperature on the occurrence of amorphous-to-ordered complexion
transitions. Bulk Cu-Zr and Cu-Zr-Hf alloy samples were annealed to induce
boundary premelting and then quenched through a procedure that induces a
gradient of local cooling rate through the sample height. Amorphous complexion
thickness distributions were found to be invariant to local cooling rate in the
Cu-Zr-Hf alloy, demonstrating enhanced stability of the amorphous complexion
structure compared to the Cu-Zr alloy, which had thinner amorphous complexions
in the regions that were slowly cooled. The experimental results are used to
construct time-temperature-transformation diagrams of the amorphous-to-ordered
complexion transition for both the binary and ternary alloys, enabling a deeper
understanding of the influence of cooling rate and grain boundary chemistry on
complexion transitions. The critical cooling rate necessary to avoid complexion
transitions in the ternary alloy is found to be at least three orders of
magnitude slower than that for the binary alloy.
