Short-Range Ordering in Unaged High-Entropy Materials

The prospect of local chemical ordering in high-entropy materials has received significant attention, but there remains little consensus on the issue. Fundamental questions, such as the role of compositional complexity and the quantitative degree of order expected in quenched or slow-cooled samples, appear largely unanswered. These topics are addressed from a theoretical perspective while drawing on a range of experimental studies. Transferable thermodynamic principles are extracted from lattice models for several types of systems with an emphasis on face-centered cubic alloys. In particular, phenomenological Landau theory is used to determine the forms of order that can arise above a critical temperature in many-component systems; these structures may differ from those obtained from long-term annealing below the critical temperature. The ability of various experimental techniques, such as electron microscopy and resistivity measurements, to directly or indirectly detect this form of order is also discussed.