What is it about?
Entropy-related phase stabilization can allow compositionally complex solid solutions of multiple principal elements. The massive mixing approach was originally introduced for metals and has recently been extended to ionic, semiconductor, polymer and low-dimensional materials. Multielement mixing can leverage new types of random, weakly ordered clustering and precipitation states in bulk materials as well as at interfaces and dislocations. The many possible atomic configurations offer opportunities to discover and exploit new functionalities, as well as to create new local symmetry features, ordering phenomena and interstitial configurations. This opens up a huge chemical and structural space in which uncharted phase states, defect chemistries, mechanisms and properties, some previously thought to be mutually exclusive, can be reconciled in one material. Earlier research concentrated on mechanical properties such as strength, toughness, fatigue and ductility. This Review shifts the focus towards multifunctional property profiles, including electronic, electrochemical, mechanical, magnetic, catalytic, hydrogen-related, Invar and caloric characteristics. Disruptive design opportunities lie in combining several of these features, rendering high-entropy materials multifunctional without sacrificing their unique mechanical properties.
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Why is it important?
Materials have always played a pivotal role in the development of human society. The range of accessible phase states, kinetics, transformation phenomena and properties, however, has been constrained by the fact that many materials used today are mostly based on one or two principal elements and typically use further elements only in low fractions.
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This page is a summary of: Multifunctional high-entropy materials, Nature Reviews Materials, September 2024, Springer Science + Business Media,
DOI: 10.1038/s41578-024-00720-y.
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Entropy-related phase stabilization can allow compositionally complex solid solutions of multiple principal elements. The massive mixing approach was originally introduced for metals and has recently been extended to ionic, semiconductor, polymer and low-dimensional materials. Multielement mixing can leverage new types of random, weakly ordered clustering and precipitation states in bulk materials as well as at interfaces and dislocations. The many possible atomic configurations offer opportunities to discover and exploit new functionalities, as well as to create new local symmetry features, ordering phenomena and interstitial configurations. This opens up a huge chemical and structural space in which uncharted phase states, defect chemistries, mechanisms and properties, some previously thought to be mutually exclusive, can be reconciled in one material. Earlier research concentrated on mechanical properties such as strength, toughness, fatigue and ductility. This Review shifts the focus towards multifunctional property profiles, including electronic, electrochemical, mechanical, magnetic, catalytic, hydrogen-related, Invar and caloric characteristics. Disruptive design opportunities lie in combining several of these features, rendering high-entropy materials multifunctional without sacrificing their unique mechanical properties.
Introduction to some Multifunctional High Entropy Alloys
Entropy-related phase stabilization enables compositionally complex solid solutions of multiple principal elements. Originally introduced for metals, this massive mixing approach now extends to ionic, semiconductor, polymer, and low-dimensional materials. Multielement mixing leverages random, weakly ordered clustering and precipitation states in bulk materials, as well as at interfaces and dislocations. The vast atomic configurations create new local symmetries, ordering phenomena, and interstitial configurations. This opens a massive chemical and structural space where previously exclusive phase states, defect chemistries, and properties can coexist in a single material. While earlier research focused on mechanical properties like strength, toughness, and ductility, this Review shifts toward multifunctional profiles—including electronic, electrochemical, magnetic, catalytic, hydrogen-related, Invar, and caloric characteristics. Disruptive designs now combine these features, rendering high-entropy materials multifunctional without sacrificing their unique mechanical performance. Historically, material development has been constrained by a reliance on one or two principal elements, limiting accessible phase states and transformation phenomena. Compositionally complex high-entropy alloys (HEAs) overcome this limitation. Originally, the goal was stabilizing equimolar solid solutions of five or more elements via enhanced configurational entropy. Today, the concept is broader, encompassing materials with large solid solution ranges that are enthalpy-stabilized rather than entropy-stabilized. Because fully stable random solid solutions are rare, many of these metastable materials benefit from ordering effects and precipitation. Beneficial properties emerge from random solid solution states—such as high lattice distortions and atomic-scale symmetry breaking—allowing kinetics, microstructure, and processing to serve as additional design variables. Furthermore, HEAs do not need to be strictly equimolar, provided no single matrix element dominates. This design approach applies to both bulk materials and internal interfaces. Interfaces are as crucial as the bulk for catalysts, hard magnets, topological materials, and coatings, and the two are chemically connected under near-equilibrium conditions through the Gibbs adsorption isotherm. These relaxed-constraints design opportunities for multicomponent materials provide access to continuously variable chemical compositions and diverse microstructural phenomena. Kinetics, non-equilibrium phase transformations, and chemical ordering produce a rich underlying lattice defect cosmos—including point defects, dislocations, stacking faults, and surfaces—serving as a highly versatile material design toolbox. The resulting microstructures differ profoundly from those in conventional alloys because lattice defects can be chemically decorated. This unique defect decoration can be strategically utilized to alter their kinetic, thermodynamic, and functional features.
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