Development of High‐Entropy Materials: A Review of Milestones Over the Last 20 Years

The concept of high‐entropy alloys (HEAs), introduced in 2004, revolutionized alloy design by focusing on multiprincipal element systems. Most research on HEAs emphasized new compositions with promising mechanical, physical, chemical, and functional properties, and their interrelated mechanisms. However, significant milestones are placed in the early stage, letting the progress in theoretical understanding and alloy design have a large jump. This review identifies those milestones in sequence. They include finding multielement crystal structures in HEAs, establishing first phase diagram, setting phase formation rules, proposing the four core effects: high entropy, severe lattice distortion, sluggish diffusion, and cocktail, using molecular dynamics simulations to understand the atomic‐level phenomena. In addition, eutectic alloys and superconducting alloys are also created. By extending the “high entropy” concept to ceramics, different ceramic and coatings, powders, bulks have been synthesized to have special properties. Similarly, high‐entropy polymers have been investigated with their unique physical and chemical behaviors to show many potential applications. All these milestones let the field become wide opening and led to some new compositions with cutting‐edge applications. In the future, there is still a huge space to develop new materials based on “high entropy” concept.