| High entropy alloys (HEAs) are a class of materials that differ from traditional alloys by containing multiple principal elements, typically five or more, in near-equimolar proportions. This unique composition leads to a high level of disorder or "entropy" in the alloy's structure, which provides remarkable properties such as enhanced strength, corrosion resistance, and thermal stability. Unlike conventional alloys, which usually consist of one primary element, HEAs form complex solid solutions rather than intermetallic compounds. These materials are gaining attention for their potential applications in industries requiring high-performance materials under extreme conditions, including aerospace, energy, and defense.
Table 820 lists various types of HEAs, which are characterized by different base elements and unique combinations.
Table 820. Categories of high entropy alloys (HEAs).
| Category |
Example |
Details |
| Face-Centered Cubic (FCC) High Entropy Alloys |
CoCrFeMnNi, MnFeCoNiCu |
The CoCrFeMnNi alloy, often referred to as the "Cantor alloy," is one of the most studied HEAs. It exhibits excellent ductility and fracture toughness, making it suitable for applications requiring high mechanical performance. |
| Body-Centered Cubic (BCC) High Entropy Alloys |
NbMoTaW |
The NbMoTaW alloy is known for its high melting point and excellent thermal stability. It's suitable for use in high-temperature environments, such as turbine blades and nuclear reactors. |
| Dual-Phase (FCC + BCC) High Entropy Alloys |
AlCoCrFeNi |
The AlCoCrFeNi alloy combines FCC and BCC phases, leading to a balance of strength and ductility. The addition of aluminum improves the alloy’s strength while maintaining reasonable toughness. |
| High Entropy Superalloys |
NiCoCrAlTi |
These alloys are designed for high-temperature applications, often used in turbine engines and aerospace components. The high entropy design provides excellent resistance to creep and oxidation. |
| Refractory High Entropy Alloys |
HfNbTaTiZr |
Refractory HEAs are engineered for extreme environments, such as those found in space and nuclear reactors. This group of alloys exhibits exceptional strength and stability at high temperatures. |
| Lightweight High Entropy Alloys |
AlLiMgScTi |
This category focuses on reducing density while maintaining good mechanical properties. Lightweight HEAs are particularly useful in applications such as automotive and aerospace where reducing weight is critical. |
| High Entropy Oxides (HEOs) |
(CoCuMgNiZn)O |
Unlike metallic HEAs, HEOs are complex oxides with multiple metal cations. They are being explored for their unique electrical, thermal, and catalytic properties. |
|
