Since the first commercial air travel was established in the early 1900s, air travel has become as commonplace as riding on a bus or driving a car. In fact, around six-million people fly on an aircraft each day. With so many people relying on air travel for work and leisure, researchers are continually improving aircraft technology.
Jet engines are very powerful, and they produce a lot of heat. The materials used in these super-high-heat environments are called superalloys. These high-heat-resistant metals are usually either a nickel- or cobalt-based alloy. They can tolerate temperatures around 1000°C (or 1832°F).
Researchers from Ames National Laboratory have discovered a new alloy that can replace nickel- and cobalt-based superalloys in gas turbines for both aviation and power generation. They used a computational framework that predicts metal phase stability, strength, and ductility based on the types of atoms involved. The framework can very quickly test thousands of material combinations. It was originally developed and experimentally validated by Ames Lab researchers.
Nicholas Argibay, a scientist at Ames Lab and leader of the research team, explained that gas turbines are more efficient when they operate at higher temperatures, around 1400°C (or 2552°F). Given these high operating temperatures, the heat tolerance limits of nickel- and cobalt-based superalloys have been a limiting factor in improving energy efficiency.
“We currently use cooling and other tricks to try to make those engines run very hot, but ultimately we are limited by the melting temperature of those materials,” said Argibay. “There are about nine elements that melt at much higher temperatures than nickel and cobalt, and those are called refractory metals. The reason we don't use those metals now is because they're brittle at low temperatures they're hard to manufacture and shape into parts.”
A solution to the challenges posed by refractory metals is to combine them into multi-principal-element alloys. Multi-element alloys are not based on one metal that holds everything together, like a nickel- or cobalt-based alloy. Instead, multi-element alloys consist of three or more elements, none of which exceeds 50% of the overall composition.
“We've come to understand that combining many of these otherwise brittle pure elements in significant amounts creates atomic structures that have emergent, unique, properties,” Argibay said.
Determining the materials and the appropriate amounts of each is where the computational framework played an important role. The framework was developed by two Ames Lab scientists, Prashant Singh and Duane Johnson, who collaborated with Argibay on discovery of the new alloy.
“When we are talking about more than three elements, mixing them together, we are talking about millions of combinations to search for, and when you do it serendipitously, it is going to take a lot of time,” said Singh.
“We put together a theory-guided methodology that interfaces with experiments. It points the experimentalists in the right direction for new alloys with the specific properties that they want to have in those materials,” said Johnson.
This new multi-element alloy is more resilient to deformation at higher temperatures than the alloys currently in use, which means that the material can be exposed to much hotter temperatures and eliminates the need for cooling the engine which causes energy loss.
Thanks to its unique composition, this alloy also has the necessary ductility properties to make it suitable for manufacturing using commercially established methods. For example, it can be deformed at room temperature, such as by cold-rolling into a sheet. This process reduces the energy needed for manufacturing overall and allows the material to retain its durability. Other refractory metals need to be heated during the manufacturing process, often above the melting temperatures of steels and superalloys, which makes them much more difficult to shape.
Argibay, Singh, and Johnson emphasized that the effectiveness of the framework in conjunction with the successful discovery of the new multi-element alloy are what make this project important. The framework is something that can be used for a variety of purposes related to materials discovery, saving both time and money. The discovery of this new multi-element alloy is a breakthrough in improving energy efficiency and costs for the aerospace industry and paves the way for further improvements in materials and technology in related areas.
“If we hadn’t had the team that we have at Ames Lab, I’m not sure if we would have validated the material. There were a lot of stumbling blocks that we managed to avoid through decades of aggregated experience with materials, processing, purification, and so on,” said Argibay. “For me, it's a career highlight to see something, in a world that's so set on artificial intelligence and big data and so on, to just see a simple equation and a table turn into something as powerful as an alloy design, where the first shot we get it right.”
Ames National Laboratory is a U.S. Department of Energy Office of Science National Laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies, and energy solutions. We use our expertise, unique capabilities, and interdisciplinary collaborations to solve global problems.
Ames Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit https://energy.gov/science.