#### Description

The development of metallic alloys is arguably one of the oldest of sciences, dating back at least 3,000 years. It is therefore very surprising when a new class of metallic alloys is discovered. High Entropy Alloys (HEA) represent such a class, a class that is receiving a great deal of attention due to their unusual combinations of strength, ductility, thermal stability, corrosion and wear resistance that make them candidates for technological applications. The term “high entropy alloys” typically refers to alloys that are comprised of 5, 6, 7 or even more elements, at or near equi-atomic composition, that form simple solid solution alloys on simple underlying lattices such as FCC and BCC. The appellation “High Entropy Alloys” refers to an early conjecture that these unusual systems were stabilized as solid solutions by the high entropy of mixing associated with the large number of components.

In this presentation, I will present a simple model that provides answers to a number of fundamental questions posed by the very existence of these alloys, not the least of which are: what are the driving mechanisms for their unexpected stability, which combinations of elements can give rise to HEAs, and how does the number of possible alloys depend on the number of constituents species? The approach is based on “high through-put” calculations of the enthalpy of formation of simple binary phases.

In particular we have developed a 31-element “enthalpy matrix” that allows one to discriminate between combinations of elements that form single-phase solid solution HEAs and similar combinations that do not. Despite the increasing entropy, our model predicts that the number of potential single-phase multicomponent alloys that can form with an increasing number of components. Interestingly, out of more than two million possible 7-component alloys considered, fewer than twenty single-phase alloys are likely.This work was supported by the Materials Sciences and Engineering Division of DOE-BES and the , a Department of Energy, .

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