Disorder-order transition in multiprincipal element alloy: A free energy perspective

Abstract

Although the concept of high entropy has flourished in the development of engineeringly important multiprincipal elemental crystalline materials, the role of entropy is controversial in driving possible disorder-order transition. Here we provide a thermodynamic perspective on this transition based on absolute free energy calculations of a list of equilibrated CoCrNi configurations extracted from the annealing history. A set of new physical quantities associated with the degree of anharmonicity, chemical short-range order, and Shannon-entropy-informed disorder temperatures are proposed to signify the disorder-order transition. The interrelationships between these thermodynamic quantities consistently suggest a disorder-order transition that is supported by experimental observation. The analysis further recognizes the critical role of the anharmonic effect in driving the random solid solution to a chemically short-range ordered phase. The free energy insights help us to understand the formation mechanism of locally ordered structures emerged from the solid solution of ideal mixing.