High-entropy materials: The future of materials engineering

Intro from Dr Janet Cotton

Our next feature on revolutionary materials development is particularly close to my heart. During my PhD, I worked on alloy development and helped create a high-nitrogen stainless steel called CROMANITE for Columbus, a 1wt% nitrogen alloy with a complex composition. This background gives me a deep appreciation for the exciting potential of high-entropy materials (HEMs), especially high-entropy alloys (HEAs).

High-entropy materials can be categorised into three types:

  • High-entropy alloys (HEAs)

  • High-entropy ceramics

  • High-entropy polymers

In this article, we’ll focus on HEAs, the metallic members of this innovative material family.

What are high-entropy materials?

High-entropy materials are advanced materials with a unique composition, typically comprising multiple principal elements in nearly equal proportions. Unlike traditional alloys that rely on a dominant base metal, HEAs are designed with five or more elements contributing roughly equal atomic percentages (usually between 5% and 35%).

Key features of high-entropy materials:

  1. Multiple principal elements: The high configurational entropy of HEAs stabilises simple solid solutions over complex intermetallic phases.
  2. Enhanced properties: HEAs exhibit remarkable characteristics, such as high strength and hardness, superior wear and corrosion resistance, and excellent thermal stability.
  3. Wide-ranging applications: These materials have uses in aerospace, nuclear energy, automotive industries, and high-temperature environments.

 

Why would you choose a high-entropy alloy?

HEAs are increasingly chosen for applications that demand an exceptional combination of properties. Here’s why:

  1. Mechanical strength and toughness: HEAs offer a high strength-to-weight ratio, making them ideal for aerospace and automotive applications. Some HEAs even retain toughness at cryogenic temperatures.
  2. Thermal stability: HEAs resist phase changes at elevated temperatures, ensuring stability in turbines and engines.
  3. Corrosion resistance: With elements like chromium and nickel, HEAs excel in harsh chemical and marine environments.
  4. Customisation: Their flexible compositions allow for tailoring properties to specific applications, from medical implants to heat exchangers.

Examples of high-entropy alloys

Alloy name Composition Unique properties Typical applications
Cantor Alloy CoCrFeMnNi High toughness and ductility; stable FCC structure Cryogenic applications, structural materials
AlCoCrFeNi Al, Co, Cr, Fe, Ni High hardness, oxidation resistance High-temperature applications, such as turbines
TiZrHfNbTa Ti, Zr, Hf, Nb, Ta High melting point, oxidation resistance Aerospace, nuclear reactors
CrMnFeCoNi Cr, Mn, Fe, Co, Ni Strength, toughness, corrosion resistance Cryogenic environments, structural materials
VNbMoTaW V, Nb, Mo, Ta, W Creep resistance, high-temperature strength Gas turbines, rocket engines

The history of high-entropy alloys

The concept of HEAs emerged in the 1990s, when researchers explored the stabilising effects of high configurational entropy. Formalised in 2004, two groundbreaking studies—one by Professor Jien-Wei Yeh in Taiwan and another by Professor Brian Cantor in the UK—laid the foundation for HEA research.

Since then, HEA research has expanded globally, with advancements driven by sectors like aerospace, defence, and nuclear energy. The focus has shifted from laboratory studies to industrial applications, supported by government-funded initiatives and collaborations between academia and industry.

 

Current availability and future standardisation

High-entropy alloys are currently available through specialised suppliers and custom alloy manufacturers, such as Goodfellow and American Elements. However, HEAs do not yet have standardised designations under systems like ASTM or ISO. As research progresses and industrial applications grow, it is expected that standardisation efforts will follow, making these materials more accessible to a broader range of industries.

 

The future of high-entropy materials

The future of HEAs is bright, with opportunities in multiple sectors:

  • Aerospace and defence: HEAs are set to revolutionise components for extreme environments.
  • Energy and nuclear industries: Refractory HEAs are well-suited for high-temperature and corrosive settings.
  • Biomedical applications: Biocompatible HEAs hold promise for implants with extended durability.
  • Sustainability: HEAs offer opportunities for recyclable and resource-efficient materials.

Advances in computational materials science, additive manufacturing, and hybrid materials development will continue to drive HEA innovation.

 

Conclusion

High-entropy alloys represent the cutting edge of materials engineering. Their unparalleled properties and versatility position them as game-changers in aerospace, nuclear energy, and beyond. As standardisation and adoption expand, HEAs will undoubtedly shape the future of high-performance materials.

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