Chaos theory: Creating nanostructured high entropy alloys

One of the biggest challenges was narrowing down the elements that would be most suitable for research on high entropy alloys. (Photos courtesy of Michel Haché.)

Nanostructured high entropy alloys have shown a lot of potential for applications in the automotive and aerospace industries. These metals, created from a mix several different elements, have shown impressive strength and stability at high temperatures when compared to regular metals. The challenge with the production of these alloys is that they are energy intensive and expensive to produce. However, researchers from University of Toronto have been working with the Canadian Light Source at the University of Saskatchewan to find less costly methods for the creation of these allows, which could generate opportunities for commercial applications.

A group of researchers from the University of Toronto have confirmed that these alloys could be created through the use of electrodeposition, the same process used for the production of chrome-plated metal parts. When comprised of a combination of metals—nickel, iron, cobalt, tungsten, and molybdenum—these alloys could withstand temperatures up to 500ºC, compared with 270ºC for pure nickel, and had increased durability.

“We’re using chaos in the material structure to bring out interesting properties,” says Michel Haché, a materials engineer at the University of Toronto who worked on the research. 

The idea for the research originated from the collaboration of Haché’s two supervisors at University of Toronto: Dr. Yu Zou and Dr. Uwe Erb. Zou had done his PhD work on high entropy alloys, while Erb had worked for about 30 years in electrodeposition and engineering applications, developing materials and processes. 

“They kind of merged together on their thoughts and put together the idea of trying to take this new class of materials, which was really only introduced around 2004, and we tried to make them using electrodeposition or electroplating. And in that way, create a very strong material, hopefully, but also one that we could make commercially in a large scale, which is kind of the big limitation right now,” Haché says.

During their research, Haché and his colleagues learned that by adding elements to an alloy they became stronger, to a point. When alloys were created using four different elements, they could withstand temperatures that were 100ºC higher than those made with three elements. However, they learned that adding a fifth element led to no further improvements.

“I started in 2018 and it was a very kind of graduated approach,” Haché says. “We started with simpler systems, three elements, and over the course of five years from 2018 to 2023, we just increased complexity as we went along—three, to four, to five elements.”

One of the biggest challenges was narrowing down the elements that would be most suitable for research on high entropy alloys.

“It’s really like throwing darts at a periodic table. The concept of high entropy alloys is you can mix whatever elements you want together, and just see what happens. So, from that standpoint, there’s just so much that you can start with and you really have to narrow that down somehow. Part of my research was putting together a way to reasonably narrow things down and find systems that would show the most promise both in applications and in actual feasibility towards making them,” Haché says.

To test the research, Haché and his colleagues were able to travel to Saskatchewan and conduct experiments at the Canadian Light Source, a national research facility of the University of Saskatchewan located in Saskatoon.

Free-standing electroplated NiFeCo foils. During their research, Haché and his colleagues learned that by adding elements to an alloy they became stronger, to a point. (Photo courtesy of Michel Haché)

“I was able to travel out there, and with the assistance of some of their staff scientists, we put together those experiments, and then I went through the data afterwards,” Haché says.

He adds that facilities like the Canadian Light Source are extremely important, not just from the pure research output, but in the training of researchers and the upcoming students coming through.

“It was such a rewarding experience to be able to go to the Canadian Light Source and to just dive deep into the world of X ray diffraction, in my case, looking at the different applications,” he says. “I took so much away from that in just pure knowledge and thinking of how I can use this in the future to answer some questions. And I pass that on to everybody else within my department.”

The next step in this research will likely prove to be the most challenging aspect: scaling up for commercial application.

“It’s certainly going to need several steps in scaling. The trickiest part is that we’ve never actually electroplated materials like this before. When we talk about electroplated materials, we typically think of pure metals—chrome, nickel, are the very conventional ones. At the very most, binary systems, something like nickel-iron that is commonly used. When we start talking about three, four, or five elements, we’ve never actually explored that on a large scale. I think that the major hurdle is going to be understanding if we can actually make these at a large scale and keep the bath chemistry in a so-called equilibrium throughout the whole process,” Haché says. “Our limitations are going to be how uniform and how thick can we actually make these materials and, therefore, that’s going to limit what applications we can use them for.”

This research has been published in the journal, Surface and Coatings Technology. Review the published journal article, “Thermal stability of electrodeposited nanostructured high-entropy alloys.”