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

Although the concept of high entropy has flourished in the development of engineeringly important multi principal 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.

Automated summary

We provide a thermodynamic perspective on the disorder-order transition in high entropy materials based on absolute free energy calculations. We propose new physical quantities to signify this transition and discuss their interrelationships. The analysis recognizes the critical role of the anharmonic effect in driving the transition and helps us understand the formation mechanism of locally ordered structures.