A selected history of the high-entropy alloy (HEA) field is provided, emphasizing the first publication in 1788 and the sometimes hidden years in the modern era before the landmark publications in 2004. A summary evaluation of the four core effects shows that a clear consensus has not yet been reached, partly because the field has expanded so much since the core effects were first posed and partly because the core effect wording is imprecise and open to interpretation. A selected list of important HEA milestones achieved since 2004, together with a continually growing number of publications, draws an optimistic picture for the future of the field. However, the HEA field is missing one essential milestone—the first major application of economic and societal impact. We recognize that a new scientific idea has a finite lifetime, and so we introduce a keen sense of urgency to accelerate future HEA studies toward new scientific advances and the first application. Two strategies are suggested to converge more rapidly on these goals: implementing the growing field of autonomous R&D, and focusing on uncontested composition space. Initial steps are already being taken on the first strategy; continued work is encouraged. Four new ideas are introduced to develop the second strategy. First, complex concentrated alloys (CCAs) are already accepted to have as few as three principal elements, and we expand their composition range to allow a maximum concentration of 75 at. percent. Next, we recognize that a small number of extraordinary commercial alloys already satisfy this expanded definition; these are called commercial CCAs. Compositional domains already well-populated by commercial CCAs are deemed to have a relatively low probability of major scientific or practical advances. The third new idea is that there is a hidden HEA penalty—the larger is the number of principal elements, the harder it is to produce extreme properties, especially for properties that follow a rule of mixtures such as stiffness, density, and even melting temperature. This gives a dynamic tension, and results over the past 20 years are hinting that the most attractive properties may often be found in alloys with as few as three principal elements. Finally, future studies are encouraged to supplement the initial approach to define HEA families based on chemically similar elements, as has been done for the 3d transition-metal, refractory metal, noble metal, and lanthanide metal HEAs. Future HEAs are encouraged to more assertively explore novel palettes of elements drawn from two or more of the existing alloy families, and from a more diverse range of elemental behaviors. All three HEA founders questioned unspoken assumptions and artificial boundaries to open new realms of exploration. We learn from these examples and continue to push beyond the new borders of thought that have emerged within the HEA field. Graphical abstract

High-entropy alloys: A rich history and a challenge for the future

期刊论文
发表日期：

2025年8月26日

查看全文

D. B. Miracle

摘要

A selected history of the high-entropy alloy (HEA) field is provided, emphasizing the first publication in 1788 and the sometimes hidden years in the modern era before the landmark publications in 2004. A summary evaluation of the four core effects shows that a clear consensus has not yet been reached, partly because the field has expanded so much since the core effects were first posed and partly because the core effect wording is imprecise and open to interpretation. A selected list of important HEA milestones achieved since 2004, together with a continually growing number of publications, draws an optimistic picture for the future of the field. However, the HEA field is missing one essential milestone—the first major application of economic and societal impact. We recognize that a new scientific idea has a finite lifetime, and so we introduce a keen sense of urgency to accelerate future HEA studies toward new scientific advances and the first application. Two strategies are suggested to converge more rapidly on these goals: implementing the growing field of autonomous R&D, and focusing on uncontested composition space. Initial steps are already being taken on the first strategy; continued work is encouraged. Four new ideas are introduced to develop the second strategy. First, complex concentrated alloys (CCAs) are already accepted to have as few as three principal elements, and we expand their composition range to allow a maximum concentration of 75 at. percent. Next, we recognize that a small number of extraordinary commercial alloys already satisfy this expanded definition; these are called commercial CCAs. Compositional domains already well-populated by commercial CCAs are deemed to have a relatively low probability of major scientific or practical advances. The third new idea is that there is a hidden HEA penalty—the larger is the number of principal elements, the harder it is to produce extreme properties, especially for properties that follow a rule of mixtures such as stiffness, density, and even melting temperature. This gives a dynamic tension, and results over the past 20 years are hinting that the most attractive properties may often be found in alloys with as few as three principal elements. Finally, future studies are encouraged to supplement the initial approach to define HEA families based on chemically similar elements, as has been done for the 3d transition-metal, refractory metal, noble metal, and lanthanide metal HEAs. Future HEAs are encouraged to more assertively explore novel palettes of elements drawn from two or more of the existing alloy families, and from a more diverse range of elemental behaviors. All three HEA founders questioned unspoken assumptions and artificial boundaries to open new realms of exploration. We learn from these examples and continue to push beyond the new borders of thought that have emerged within the HEA field.

Graphical abstract