High Entropy Alloys: From Random Atoms to the Metals of The Future
What are High Entropy Alloys? And how might they herald a new generation of high temperature applications? In our quest to understand them better we asked a young physicist, Isaac Hooper, to give us his assessment.
In the search for new metallic structures to withstand high temperatures, creep and corrosion resistance, High Entropy Alloys, could be a winner.
But what are they?
High Entropy Alloy (HEA) simply means a group of more than one metallic element mixed together, almost like putting squash in your water.
‘Entropy’ is a term that describes how random states exist (in this case 'elements') in a system ('the alloy'). Therefore, High Entropy would suggest a high level of randomness in the layout of elements in the alloy, almost like a pot of colouring pencils, or balls in a ball pond, each pen-tip or coloured ball being a different colour to others nearby and forming a random assortment of colours. I imagine that if you assigned a different colour to each element in an HEA, the result would be very similar. Therefore, a High Entropy Alloy is an alloy made up of several elements randomly assorted in its structure.
The original definition was that HEAs are alloys consisting of 5 or more elements, randomly assorted throughout the alloy in “equiatomic proportions” - which simply means each of the elements are in equal quantities. The reason this is fascinating is the absence of the annoying side effect in regular alloying called an intermetallic compound. When alloying just two or three metals together, it is normal to obtain a high amount of one metal and only smaller or trace amounts of the others - this is to prevent the alloy becoming an intermetallic, the phase when the individual metals accumulate into intermetallic regions as a result of too high a quantity of other metals being added. They form boundaries between each element and create intermetallics - which is not usually the desired result. These are usually brittle and difficult to deform which limits their practical uses.
For some reason, not yet fully understood, High Entropy Alloys do not do this. The universe decided, it seems, that if you wanted to alloy two or three metals then it would just decline the attempt and give you intermetallics. But if you wanted to alloy five or more elements with equiatomic proportions then you’re suddenly able to do so.
The structure of HEAs is also quite interesting. As we have noted, the distribution of elements within an HEA is, to the naked eye, random. (This is because nothing is truly random except the half-life of unstable radioactive isotopes). But the lattice structure is severely deformed.
This occurs because in the HEA alloy each atom is surrounded by different types of atom and so suffers lattice strain mainly because of the atomic size differences. It is also due to the differing bonding energies and non-symmetrical bindings.
The question for material scientists in the field of high temperature applications (such as ‘High Pressure Turbine blades’ in gas turbine engines) is whether HEAs ‘with rhenium’ could compete with, or even replace, single crystal superalloys (SX).
These SX alloys are basically just a nickel base structure with a variety of trace elements thrown in for strength and other useful properties, grown from a molten group of elements through a ceramic core into a single crystal of the shape required.
Rhenium is one of the best (if not the best) metal to add to an SX alloy because of the way it migrates to the gamma prime phase of the crystal, its heavy atoms anchoring the microstructure within the single crystal. The addition of rhenium to nickel-base SX alloys dramatically improves the alloy’s creep resistance which means a rhenium bearing alloy of this kind is a lot less likely to deform and stretch while performing at high temperatures (close to 1100°C).
The reason SX alloys work so well is because they have a very consistent and regular structure, no discrepancies, no intermetallics - just pure crystal. In this way they can withstand an extraordinary amount of heat, and they are currently used by manufacturers such as Rolls-Royce, Pratt & Whitney and GE and are hidden away in the hottest part of the engine.
What is highly interesting is that HEAs, such as alloy GRX-810, developed by NASA, also contains rhenium, and has been shown to have most of the same properties but unlike SX the alloy is designed for 3D Printing not casting. And yet GRX-810 is designed for extreme temperature applications including turbine blisks and rocket engine injector nozzles.
Despite the all the promising work being done with the alloy, due to the lack of extensive research on its deformation resistance, and “the influence of microstructural features on mechanical properties at different temperatures and varying geometric thicknesses”, (how the structures inside the material affect how easily it deforms, at different temperatures and at different thicknesses), the alloys are not quite ready for full commercial roll-out.
When you search GRX-810 on the internet, what comes up first is NASA’s webpage on how they’re producing the alloy as they are at the forefront – at least publicly. Here it is cited that they use a very precise 3D printing technique which “dramatically improves the strength and durability of the components and parts used”.
GRX-810 has been tested to withstand temperatures upwards of 1100°C, much like the SX alloys mentioned earlier. And, because of this, it is suggested they could be used to build aerospace parts and have major implications for sustainable propulsion systems in the future.
The alloy’s high durability means, when used in jet engines, there is reduced fuel burn and, in turn, lower operating and maintenance costs. And furthermore, engine manufacturers will be able to commercialise much lighter materials with at the same time an improvement in performance. They can now make trade-offs in cost of raw materials and manufacture that, until now, could not have been considered without sacrificing performance.
One area of study will undoubtedly be how GRX-810 handles the cryogenic temperatures found in space. And more importantly, how it handles the transition from the high temperatures it can withstand to extreme lows. Does it become brittle and snap or crack - or does it stay strong? If the latter is possible, we might soon see HEAs being used in satellites. At least it seems likely that this rhenium-bearing HEA will be used (if it isn’t already) by jet engine manufacturers and will be a major generational change in the aerospace field.
We know that HEAs such as GRX-810 can be used in the aerospace field thanks to NASA and other such organisations. But what else might they be used for?
I got in touch with Tom Butcher who has recently written an article for MMTA’s The Crucible magazine (August 2026 edition), also on HEAs. I asked him which applications of HEAs he felt we might see eventually. One of his answers was that they might possibly be used in nuclear reactors where parts are extraordinarily difficult to replace and manage. But because of the ultra-high levels of safety required in nuclear applications it may be decades before HEAs are introduced. But the aim might be to coat components, to not only give them a high temperature resistance but also add hardness and ductility as they might be less likely to corrode in such exposed conditions.
The only predictable setback is the length of time needed to prove their reliability.
As HEAs are a relatively new discovery in the material science world (only discovered in 2004) we do not know how they will perform over time as we have not been able to subject them to 40+ years of such conditions. We’ve only just made it past their 20th birthday after all. The other drawback is of course the cost, which needs to be measured against their predicted usefulness and reliability. If HEA parts are not able to stand the test of time, or the testing environment in which they are required, any cost savings will be outweighed in comparison to the incumbent alloys.
So, all in all, HEAs are an extraordinary breakthrough in the world of harnessing elements to man’s use. Even though it may take some time for us to see them produced on a commercial scale, we would not be over optimistic to hope they will be applied in the future.
If so, the debt will be to pioneering scientists such as Jien-Weh Yeh, (affectionately known as the father of High Entropy Alloys), for his work to bring these metals into the limelight.
It is clear that anyone interested in high temperature materials will certainly be following the advancements made with High Entropy Alloys.
Who knows they may be applied in an aeroengine near you someday!
Isaac Hooper
23.08.26
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