Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys

TL;DR

This study investigates how cooling rates affect the stability of amorphous complexions in Cu-based nanocrystalline alloys, revealing that ternary alloys have significantly higher stability against complexion transitions than binary alloys.

Contribution

It provides the first detailed analysis of critical cooling rates for amorphous-to-ordered complexion transitions in Cu alloys, highlighting the stabilizing effect of ternary alloying.

Findings

Ternary Cu-Zr-Hf alloys exhibit more stable amorphous complexions than binary Cu-Zr alloys.

Critical cooling rate for ternary alloys is at least three orders of magnitude slower.

Time-temperature-transformation diagrams elucidate complexion transition behaviors.

Abstract

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.