PNNL researchers (from left) Isabella van Rooyen, Subhashish Meher, and Steven Livers are part of the team that developed a durable new nickel-based “super alloy” by replacing cobalt with manganese. (Photo: Andrea Starr/PNNL)
Pacific Northwest National Laboratory has reported that researchers there have created a tough new alloy that has potential use in advanced nuclear reactors and that is not dependent on a difficult-to-get element. The research team, which included materials scientists Isabella van Rooyen, Subhashish Meher, and Steven Livers, started its experiments with the highly durable nickel-chromium-cobalt-molybdenum “super alloy” known as Inconel 617 (IN617).
IN617 is considered attractive for use in such advanced units as molten salt reactors, gas-cooled fast reactors, and very-high-temperature gas-cooled reactors, as well as applications in other extreme conditions, because it maintains its strength at high temperatures, resists oxidation and corrosion, and displays low thermal expansion.
However, cobalt is a “critical material” that can be hard to get in the United States because most of it is produced in Congolese mines that are controlled by China. The PNNL team stripped the cobalt out of IN617 and replaced it with easier-to-obtain manganese, making an alloy they dubbed IN617-M1. Tests of their modified creation indicated that “the new alloy could be a competitive alternative to IN617,” according to a PNNL news release on the project.
Methods: The researchers determined that manganese might be a viable alternative for cobalt by performing computer simulations of the molecular dynamics of different alloy compositions. After the computer simulations suggested that manganese was a good candidate, they fabricated the modified alloy through a traditional casting method and through the advanced friction stir consolidation method. The latter method is based on the application of mechanical energy and friction heat, rather than melting, allowing for microstructure tailoring.
Experimental results: Finally, the researchers conducted tests to compare their modified IN617-M1 with the nonmodified IN617 alloy. The tests included electron microscopy analysis, hardness tests, and corrosion resistance modeling.
According to PNNL, early computational analysis on corrosion resistance, high-temperature stability and durability, and hardness show promising results for IN617-M1, with properties similar to those for IN617. In addition, the advanced fabrication method potentially could result in creating alloys with even better properties, while decreasing the dependence on critical materials.
Next steps: The PNNL researchers are following up on their promising experiments by seeking collaborators in industry. Goals include scaling up the material synthesis and demonstrating the alloy for multiple applications.
