Creating nanoalloys that actually prefer extreme environments using amorphous interfacial complexions

Nanocrystalline materials are unfortunately often an exercise in futility. The same grain refinement that gives high strength or a high density of sinks for radiation damage only means that the material is more unstable against coarsening. In this talk, we discuss how the incorporation of disordered complexions into the grain boundary network can stabilize nanocrystalline materials at very high temperatures. Since these features occur due to premelting transitions near the melting temperature, they are actually stable in this extreme environment. We show that the incorporation of amorphous intergranular films can lead to grain size stabilization over long periods of time, create new high temperature stability regimes, and allow for the formation of bulk nanocrystalline alloys with small grain sizes. Our initial experiments are performed in Cu-rich alloys, but we also demonstrate the extension of this concept to new material systems such as lightweight Al-rich alloys and alloys with compositionally complex grain boundaries. In addition to experiments, atomistic modeling is used to understand the entire complexion population inside of a polycrystalline grain boundary network. As a whole, this work proves that interfaces can be designed to prefer the extreme environments in which we hope to use them.