High-temperature stability and grain boundary complexion formation in a nanocrystalline Cu-Zr alloy

TL;DR

This study demonstrates that Zr doping in nanocrystalline Cu significantly enhances thermal stability by promoting grain boundary complexion formation and ZrC precipitation, maintaining high strength after high-temperature annealing.

Contribution

It reveals how Zr segregation and complexion formation improve the thermal stability of nanocrystalline Cu alloys, a novel approach for durable nanostructured materials.

Findings

Zr segregation leads to amorphous complexion formation at grain boundaries.

Grain growth is significantly retarded at high temperatures.

High mechanical strength is retained after annealing.

Abstract

Nanocrystalline Cu-3 at.% Zr powders with ~20 nm average grain size were created with mechanical alloying and their thermal stability was studied from 550-950 {\deg}C. Annealing drove Zr segregation to the grain boundaries, which led to the formation of amorphous intergranular complexions at higher temperatures. Grain growth was retarded significantly, with 1 week of annealing at 950 {\deg}C, or 98% of the solidus temperature, only leading to coarsening of the average grain size to 54 nm. The enhanced thermal stability can be connected to both a reduction in grain boundary energy with doping as well as the precipitation of ZrC particles. High mechanical strength is retained even after these aggressive heat treatments, showing that complexion engineering may be a viable path toward the fabrication of bulk nanostructured materials with excellent properties.