Paving the way to safer power by controlling the behavior of complex alloys
Eva Zarkadoula

Increasing complexity results in a better response of nickel-based alloys to radiation. Image courtesy of Yanwen Zhang, Energy Dissipation to Defect Evolution Energy Frontier Research Center

How do you make better materials for nuclear reactors? What makes materials work well even after being exposed to radiation? How can we control the materials’ behavior to make it last longer?

These are some of the questions that inspire scientists at the Energy Dissipation to Defect Evolution (EDDE) Energy Frontier Research Center. In an irradiation environment, fast-moving particles travel through materials. These particles transfer their energy to the material’s atoms. This energy knocks the atoms out of their ordered positions, resulting in defects: imperfections in the arrangement of the atoms. The creation of these defects is what is called radiation damage. The scientists at EDDE are studying how energy dissipates in matter, and they are finding ways to control the defect — or the damage — evolution to design radiation-tolerant materials.

Solid, uniform mixtures of metal atoms. The EDDE team is thoroughly investigating a family of new materials: solid solution nickel-based alloys. These alloys, with nickel as the base, are mixtures of two to five metals, including iron, chromium, cobalt, manganese, and palladium. The random arrangement of the mixed atoms of these metals can lead to special properties, such as how they conduct heat and affect the defect behavior. For example, the team at EDDE has shown that the more complex the alloys are, the more heat from irradiation can be localized. As a result, more defects may be “healed” to suppress damage evolution, leading to an improved radiation resistance. Building special properties into the alloys can make materials better suited for specific applications in nuclear reactors. A possible application is for structural materials that come in contact with the hot plasma in future fusion reactors. The team is exploring the fundamental properties of these designer alloy materials to best match them to real-world applications.

Using a plethora of experimental methods and computational techniques, EDDE members determined the radiation response of different combinations with nickel. By understanding the damage created during irradiation, they are tailoring the alloy composition in a way that favors the resistance to radiation. Good radiation resistance of materials means that they can be used for longer, making applications in extreme conditions safer, as well as lowering maintenance costs.

Increasing the alloy complexity — in other words, adding a certain amount of specific elements to the nickel-based alloy — affects the interactions of the atoms and the electrons. The EDDE researchers are looking at the ways these interactions affect the materials’ properties and the way the energy dissipates in the material. By understanding these interactions, the creation and evolution of the defects can also be understood and ultimately controlled.

Increasing complexity for good response to radiation. Following this path, the EDDE team has found that certain combinations of metals significantly alter the material's thermal and defect properties, and the energy transfer in the system. The scientists have established, for example, that alloys consisting of three or four metal species can withstand more radiation than alloys made of two components. They showed that increasing complexity results in less damage, indicating a better response to irradiation.

They have also determined that increasing the iron content results in small defect structures. This shows that the alloy composition affects the way the defects interact. The alloy composition also affects how big or small of structures are formed during the defects' interactions, which can also make the materials more resistant to radiation. Of course, with so many options of metal elements to choose from, combined with the random positions of the atoms in these solid solutions, further exploration of the interesting character of these materials is necessary.

Space: Further applications of this fundamental research. The strong synergy among EDDE scientists highlights how experimental and computational methods complement each other in approaching the same challenge. Combinations of experiments, simulations, and theoretical calculations explain the interaction of radiation with the alloys, down to the behavior of atoms and electrons. By using empirical experiments and computer simulations, the scientists can explore the system from different aspects.

EDDE’s contribution to science does not stop there. The science conducted in EDDE, while targeting the development of materials for nuclear energy applications, contributes to the wider material science community. Understanding how energy dissipates, creates damage, and alters properties is the key to designing new materials for technologies in places where extreme temperature and pressure develop. Such an example is satellites and other space devices with materials that are exposed to cosmic radiation. Knowledge gained from EDDE’s mission can be extended to other materials, providing a foundation for the development of new technologies.

Oak Ridge National Laboratory is the lead of EDDE and has six partners across the United States: Lawrence Livermore National Laboratory, the University of Michigan, the University of Tennessee, the University of Wisconsin-Madison, the University of Wyoming and Virginia Tech. EDDE is funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

About the author(s):

Eva Zarkadoula, a member of the Energy Dissipation to Defect Evolution Energy Frontier Research Center, is a R&D associate in Oak Ridge National Laboratory. The main focus of her work is the interaction of radiation with matter and the fundamental effects of electronic excitations in the energy deposition, damage creation, and micro-structural alterations, which she investigates with the use of modeling techniques. Eva received her Ph.D. in physics from Queen Mary University and a B.Sc. in physics from the University of Athens. She strongly believes that the combination of modeling and experiments is essential to obtain a fundamental understanding of the processes that take place at the atomistic level during irradiation.