Researchers at the Department of Energy’s Pacific Northwest National Laboratory realized that sometimes developing new materials can be akin to creative baking—where substituting ingredients and making simple adjustments can lead to surprising benefits. 

In this case, they are studying the “recipe” for producing a durable alloy for nuclear reactors and other energy applications. 

Their work centered on replacing cobalt with manganese in an alloy known as Iconel 617, or IN617 for short. Nickel-based “super alloys,” such as IN617, are used in gas turbines, space vehicles, chemical equipment, power plants and nuclear reactors. 

IN617 is durable in extreme environments because it maintains its strength in high temperatures, resists oxidation and corrosion, has low thermal expansion and can be welded easily. 

For these reasons, this alloy also is attractive for use in new nuclear energy generation technologies such as molten salt reactors, gas-cooled fast reactors and very high-temperature gas-cooled reactor systems.

Cobalt, however, is considered a critical material due to supply chain risks, with cobalt mining and refinery production already at a record high in 2024. Moreover, more than 75 percent of the world’s raw cobalt comes from mines in the Democratic Republic of Congo—and China owns or controls the vast majority of their output. China also is the world’s leading producer of refined cobalt. 

By finding a way to substitute other elements for cobalt in IN617, researchers could help reduce dependence on a critical material that is supplied nearly exclusively from outside the United States. The scientists began by conducting a feasibility study, looking at computer simulations of the molecular dynamics of potential compositions. 

Through that process, they identified manganese as a possible replacement element. To do this, the researchers used the simulations to identify five promising candidates—each with different concentrations of cobalt, chromium, manganese and molybdenum. This approach allowed the researchers to home in on a specific composition that substituted cobalt with manganese to create IN617-M1 (the M stands for modification). 

The researchers then successfully fabricated the modified alloy using two different methods to assess its economic feasibility and manufacturability. In addition to traditional casting methods, they used another technique known as friction stir consolidation. Rather than melting the metals, this technique uses specialized tools to apply mechanical energy and create friction heat. 

This advanced manufacturing method allows the materials to be “stirred” in a way that enables tailoring of the microstructure. The combination of change in composition and manufacturing method can result in even better properties while decreasing the dependence on critical materials. 

In experiments designed to validate their M1 composition, the researchers used electron microscopy and hardness tests to compare it to IN617. They also assessed corrosion resistance by modeling techniques to measure how deep oxygen would penetrate the material—with lower penetration depths indicating higher resistance and less propensity for rusting.

Early findings suggest that the new alloy could be a competitive alternative to IN617. In addition to computational analysis that revealed promising results for corrosion resistance, high-temperature stability and durability, experiments showed mechanical performance in terms of hardness was comparable to IN617. 

The scientists are seeking industry partners to collaborate on next steps, which could include scaling up the material synthesis and demonstrating the alloy for multiple applications.

Affordable nuclear energy—including the advancement of next-generation reactors—will likely play a growing role in America’s energy generation mix as our nation focuses on providing affordable, abundant electricity from a variety of sources. 

Finding ways to enable nuclear reactors and other energy technologies to operate reliably and efficiently while also reducing the need for critical materials is just one way that PNNL is moving our energy future forward. 

Steven Ashby, director of Pacific Northwest National Laboratory, writes this column monthly. To read previous Director's Columns, please visit our Director's Column Archive.