High-entropy grain boundaries

Abstract

AbstractAs high-entropy alloys receive an increasing amount of attention, an interesting scientific question arises: can grain boundaries be “high entropy”? In 2016, we proposed “high-entropy grain boundaries” as the grain boundary counterparts to high-entropy materials. Here, we discuss the underlying interfacial thermodynamics to elaborate relevant concepts. We emphasize that “high-entropy grain boundaries” are neither equivalent to grain boundaries in high-entropy materials nor simply “compositionally complex grain boundaries”, but they should possess specific thermodynamic characters. Using a simplified segregation model, we illustrate that both grain boundary and bulk high-entropy effects can reduce grain boundary energy with increasing temperature for saturated multicomponent alloys, where the effective grain boundary entropy can be positive and increase with the number of components. We show that high-entropy grain boundaries can stabilize nanocrystalline alloys at high temperatures via thermodynamic and kinetic effects. Grain boundary structural disordering and transitions may offer further opportunities to attain higher effective grain boundary entropies.