Op-Ed: What will be the first applications of high entropy alloys?
By Ben Sanders, MEng ’24 (MSE)
The following essay won the “Op-Ed category” of this year’s Berkeley MEng op-ed contest. In this contest, Master of Engineering students were challenged to communicate an Engineering-related topic they found interesting to a broad audience of technical and non-technical readers.
Note: As opinion pieces, the views shared here are neither an expression of nor endorsed by UC Berkeley or the Fung Institute.
Captain America’s shield, Iron Man’s suit and SpaceX’s rockets all have one thing in common. They are metal. No, really: they are made of the stuff. Alloys, formally defined as mixtures of metals, have allowed humanity to excel in previously unimagined ways.
For example, robust tools that can cut through hundreds of pieces of material without becoming dull! Buildings that stand taller than the largest trees! And methods of transportation that can carry us from location to destination faster and further than ever before.
Metal has shaped our vision of the future; it’s hard to call to mind a sci-fi world that is not dominated by glimmering surfaces of polished metallic wonder.
High entropy alloys (HEAs) are a newcomer to the stage, these new types of alloys have the possibility to once again change how humanity uses and thinks about metal. When most people think of alloys they think of structural applications like tools, vehicles, and transportation. But I believe because of the strong regulatory documentation needed for these applications we should push to implement HEAs first in a different direction: soft magnets.
The traditional school of thought on alloys is that they are predominately one or two materials with small additives. Take the construction steel A36, it is about 0.5% carbon and silicon, and 99.5% iron. High entropy alloys, have the potential to shake up this assumption. Containing roughly equal amounts (5 to 35%) of four or more elements, HEAs rather than being brittle and inhomogeneous, have an ordered structure with properties not obvious from their components. This has opened the field of metallurgy as there are now many more possible useful alloys, each with their own properties to explore.
Since the term HEA became popular in 2004, its conception has shifted originally the name referred to the hypothesized atomic layout of these materials as a single phase of unordered atoms. Recent findings have put this assumption of microstructure into question suggesting that rather than a single unordered phase these materials have areas of high order, like in a crystal, and low order, like in a glass.
Many at the outset had theorized that HEAs would be used in structural materials. This belief was driven not only by HEAs high measures of toughness, corrosion resistance and ductility but also because of the large degree of tunability of these properties using different concentrations of the constituent elements. The structural materials application, however, presents unique challenges.
Engineers, when choosing to use a material for a building, want to know a lot about how that material behaves so they can predict its behavior in a design. To be on a level playing field with steel HEAs would C need certificates from ASTM International, a national material standards group. Under ASTM’s classifications different applications of materials require different standards. Each of these standards includes the minimum mechanical properties across ranges of chemical composition.
This presents a problem as high entropy alloys can demonstrate large differences in properties under small changes of concentration. Not to mention additional certifications are required from producers of steel from the AISC. For many designers the lack of information on HEA behavior has been a turn-off from using HEAs in structural engineering.
Due to the large number of combinations, need for rigorous documentation, and acquisition of certificates, I believe it is unlikely that HEAs will be seen first in structural applications. Rather it is more likely HEAs will be used in specialized functional materials; Soft magnets are one such promising example. In a soft magnet there is only a small amount of energy required to the direction of the magnetic field in the material (switch the north and south poles).
Current soft magnetic materials all have something in common. They are brittle. This makes machining and handling them difficult. Due to HEAs highly tunable properties soft magnetism can be achieved with mechanical properties like ductility, making them less brittle. Annealed FeCoNiMn0.25Al0.25 an HEA according to a recent academic paper has ductility greater than twice the most common commercial soft magnet silicon steel and comparable magnetic saturation to FeNi alloys (Panpan).
Currently, several future devices of humanity require magnets.
Electric motors are indispensable in electric cars and power generation. Transformers, alternators, and other electronics are key to communications, essential for our connected future. These applications will require passing standards like structural materials, but I think the number and speed of passing such standards is lower in part because of the different cultural attitudes between structural and electronic applications.
In the case of structural applications safety is paramount, whereas in electronics, innovation rules many decisions. Beyond customizing ductility and magnetic saturation other properties of an HEA magnet, such as thermal stability, resistivity, and corrosion resistance can be tuned. This allows the creation of devices with greater energy efficiency and longer lifetimes.
I have a love of materials because they are essential for everything we make. They guide our thinking in the creation of new products and devices.
Without p and n-doped silicon, transistors and consequently computers as handheld rather than room size devices would have been inconceivable. By changing materials, you change what is possible. High entropy alloys in their ability to engage in strategic tradeoffs between properties capitalize on this fact.
May this serve as a reminder that the discovery and use of novel technology are monumental efforts. The skills for discovery of new science and application of invention are unique. By being aware of such differences and conducting science with these concepts in mind, scientists can not only upend accepted norms and increase efficiencies but also create cultural change in how people see the future and what is in it.
To high entropy and beyond!
Citations:
Galambos, Theodore. “History of the AISC Specification; 1923–2010.” American Institute of Steel Construction. History of the AISC Specification; 1923–2010 | American Institute of Steel Construction
Mikhail Slobodyan, Evgeniy Pesterev, Alexey Markov. “Recent advances and outstanding challenges for implementation of high entropy alloys as structural materials,” Materials Today Communications, Volume 36, 2023, 106422, ISSN 2352–4928, https://doi.org/10.1016/j.mtcomm.2023.106422. (https://www.sciencedirect.com/science/article/pii/S2352492823011133)
Nickle development institute, American iron and steel institute, and specialty steel institute of north America. “Design Guidelines for Stainless Steel.” Microsoft Word — 9014-Third Draft.doc (nickelinstitute.org)
Panpan Li, Anding Wang, C.T. Liu, A ductile high entropy alloy with attractive magnetic properties, Journal of Alloys and Compounds, Volume 694, 2017, Pages 55–60, https://doi.org/10.1016/j.jallcom.2016.09.186 Accessed 26 September 2023.
Xuehui Yan, Yong Zhang, “Functional properties and promising applications of high entropy alloys,” Scripta Materialia, Volume 187, 2020, Pages 188–193, ISSN 1359–6462, https://doi.org/10.1016/j.scriptamat.2020.06.017.
Yeh, JW. (2016). Overview of High-Entropy Alloys. In: Gao, M., Yeh, JW., Liaw, P., Zhang, Y. (eds) High- Entropy Alloys. Springer, Cham. https://doi.org/10.1007/978-3-319-27013-5_1 Accessed 29,2023.
