Nanocrystalline Cu-3 at.% Zr powders with ~20 nm average grain size werecreated with mechanical alloying and their thermal stability was studied from550-950 {\deg}C. Annealing drove Zr segregation to the grain boundaries, whichled to the formation of amorphous intergranular complexions at highertemperatures. Grain growth was retarded significantly, with 1 week of annealingat 950 {\deg}C, or 98% of the solidus temperature, only leading to coarseningof the average grain size to 54 nm. The enhanced thermal stability can beconnected to both a reduction in grain boundary energy with doping as well asthe precipitation of ZrC particles. High mechanical strength is retained evenafter these aggressive heat treatments, showing that complexion engineering maybe a viable path toward the fabrication of bulk nanostructured materials withexcellent properties.
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