High Entropy Alloys as Glasses and Solid Solutions—Configurational Entropy and Alloy Properties

High entropy alloys (HEAs) represent highly promising multicomponent crystals that form concentrated solid solutions (CSS) and may violate traditional thermodynamic rules of mixing, ultimately leading to excellent physical properties. Here, we report on simulations on seven CSS, including Co-Cr-Ni-Fe-Mn elements and we use 1-1 comparisons to corresponding glass phase characteristics, attained through rapid cooling protocols. We determine the behavior of various structural features, including the configurational entropy for a set of CSS in their crystalline and vitreous states numerically using swap Monte Carlo and show that the entropic rule of mixing is not always adequate for predicting alloy formation. We study the stability and formability of crystalline solid solutions, as well as glasses, while following the configurational entropy. An apparent entropic similarity between CSSs and corresponding glasses, leads us to use a Kauzmann-like ansatz, relating the CSS with the emergence of a order/disorder transition, at a composition-dependnet temperature. In the context of glasses, a comparison between kinetic and thermodynamic fragilities allows to associate the sluggish diffusion onset to a drop in configurational entropy at the Kauzmann temperature. In analogy to glasses, we classify CSS as strong or fragile in the sense of their ability to migrate across CSS crystal configurations at high temperatures. We argue that the magnitude of the order/disorder transition temperature may predictf CSS single-phase stability, as it appears to scale with well known predictors, such as the valence electron concentration (VEC).