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Spring 2016

New Path to Enhance Radiation Tolerance

Designing alloys that are more resistant to radiation damage by controlling compositional complexity

Ke Jin

This flower-like image shows the scan of crystals grown by the team, using ion channeling technique. The bottom of the “flower” indicates when the probe ions are aligned with the atom chains in the crystal. Measuring the depth of that is one of the methods that the scientists used to detect the damage of materials.

Safe operation of nuclear power plants demands structural materials that can resist severe radiation damage. While alloy development has made great progress over the past several decades, fulfilling the requirements of next-generation reactors remains challenging. Current alloy-design strategies usually attempt to trap defects by modifying the microstructure; however, the scientists in the Energy Dissipation to Defect Evolution (EDDE) Center are taking a different approach. They believe that modifying the compositional complexity of alloys could be a new path to enhance radiation tolerance.

In nuclear reactors, energetic particles deposit energy on the material, knock atoms out of their original positions, and create defects. While most initial point defects recombine and are healed, the surviving ones accumulate, migrate, and may form various defect clusters. These defects eventually compromise the material’s properties, making them, for example, brittle and swollen.

Although numerous types of alloys have been developed over thousands of years, most have only one principal element, such as iron in stainless steel or copper in bronze. Scientists at EDDE, however, are focused on an intriguing new family of alloys. These alloys contain two to five principal elements rather than one, with equal or near equal atomic concentration, while still maintaining a simple structure. What makes the alloys unique is that although macroscopically the atoms are approximately orderly aligned, each atom in these alloys has different neighbors, a different chemical environment, and is displaced from the perfect lattice position by a small amount. These alloys have exceptional mechanical properties and large application potential; however, their irradiation response remains relatively unknown.

One of the EDDE team’s hypotheses is that the disorders brought about by large compositional complexity can modify the material’s intrinsic physical properties, affect energy dissipation, and ultimately change the production and evolution of defects.

To test the theory, they first compared the transport properties of the compositionally complex alloys with those of pure nickel or simple alloys from both a theoretical and an experimental perspective. Their calculations found that the large compositional complexity not only breaks the perfect periodicity of electronic structure, but also brought in strong magnetic disorders, especially when certain elements, such as chromium, were added. Thus, the electrons in such complex alloys were expected to be more strongly scattered.

The prediction was strengthened through experimentation. They found that the measured electrical resistivity of the alloys with large compositional complexity was much larger than that in pure nickel, and consequently, the heat dissipated slower and stayed more localized in these complex alloys.

The scientists at EDDE further demonstrated that the modification on the intrinsic energy dissipation process affected the defect production and evolution in these complex alloys. Experimental analyses indicated that large compositional complexity could suppress the defect production and delay defect evolution. By observing the differences in the defect range and defect structure between the materials, the scientists discovered that the defect migration in the alloys was slower than in pure nickel. Simulation results suggest that the defects produced in the compositionally complex alloys are smaller and fewer than in nickel, which mirrors the experimental results.

Higher complexity does not equal more elements. The EDDE team realized that finding good combinations of different elements that can introduce certain local disorders might be more important than merely putting more elements together.

The EDDE scientists believe that, while just beginning, they are expanding the strategies to make structural alloys more reliable in a radiation environment, thereby improving the safety of nuclear power plants. Yanwen Zhang, director of the EDDE Center, said, “We are trying to bring new insights of energy dissipation and defect evolution that may inspire new design principles of radiation-tolerant structural alloys for advanced energy systems and for new defect engineering paradigms benefiting broader science and technology.”

Acknowledgments

This work was supported as part of the Energy Dissipation to Defect Evolution (EDDE), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES). BCS was supported by DOE, Office of Science, BES, Materials Sciences and Engineering Division. LKB acknowledges additional support from a fellowship awarded by the Fonds Québécois de recherche Nature et Technologies. Ion beam work was performed at the University of Tennessee-Oak Ridge National Laboratory Ion Beam Materials Laboratory located on the campus of the University of Tennessee, Knoxville. Electronic structure calculations were performed with Markus Däne at the Lawrence Livermore National Laboratory, which is operated by Lawrence Livermore National Security, LLC, for DOE’s National Nuclear Security Administration. This simulation used resources of the National Energy Research Scientific Computing Center, supported by the Office of Science, DOE. X-ray diffraction characterization was conducted at the Center for Nanophase Materials Sciences, a DOE Office of Science user facility. Electron microscopy was conducted at the Michigan Center for Material Characterization of the University of Michigan-Ann Arbor.

More Information

Jin K, BC Sales, GM Stocks, GD Samolyuk, M Daene, WJ Weber, Y Zhang, and H Bei. 2016. “Tailoring the Physical Properties of Ni-Based Single-Phase Equiatomic Alloys by Modifying the Chemical Complexity.” Scientific Reports 6:20159. DOI: 10.1038/srep20159

Lu C, K Jin, LK Béland, F Zhang, T Yang, L Qiao, Y Zhang, H Bei, HM Christen, RE Stoller, and L Wang. 2016. “Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys.” Scientific Reports 6:19994. DOI: 10.1038/srep19994

Zhang Y, GM Stocks, K Jin, C Lu, H Bei, BC Sales, L Wang, LK Béland, RE Stoller, GD Samolyuk, M Caro, A Caro, and WJ Weber. 2015. “Influence of Chemical Disorder on Energy Dissipation and Defect Evolution in Concentrated Solid Solution Alloys.” Nature Communications 6:8736. DOI: 10.1038/ncomms9736

About the author(s):

  • Ke Jin is a postdoctoral researcher at the Oak Ridge National Laboratory, working in the Energy Dissipation to Defect Evolution Center. His research interests include the radiation effects in materials, ion beam analysis, and alloy development.

Being Complex, Living Extreme

Scientists uncover how compositional complexity affects the energy dissipation and defect evolution in alloys

In the complex alloys, each atom has different neighbor atoms, as shown in this image, in which each color represents a kind of metal atom. The scientists in EDDE are delving into how the deposited energy from irradiation dissipates and damages the material and how the compositional complexity affects these processes. Image courtesy Ke Jin, ORNL, and Nathan Johnson, PNNL

While simplifying life helped Thoreau deal with stress, for materials, complexity might be just the ticket to survive the extreme conditions inside a nuclear reactor or outside a space satellite. At the Energy Dissipation to Defect Evolution (EDDE) Center, scientists uncovered how the chemical disorders induced from the combination of two to five metal elements slows the heat spread in an advanced structural alloy family and demonstrated that such changes might make the irradiation-induced defects harder to survive and accumulate. Knowing how such materials behave could inspire new material-design strategies for today’s reactors and tomorrow’s. EDDE is led by Oak Ridge National Laboratory.

More Information

Jin K, BC Sales, GM Stocks, GD Samolyuk, M Daene, WJ Weber, Y Zhang, and H Bei. 2016. “Tailoring the Physical Properties of Ni-Based Single-Phase Equiatomic Alloys by Modifying the Chemical Complexity.” Scientific Reports 6:20159. DOI: 10.1038/srep20159

Lu C, K Jin, LK Béland, F Zhang, T Yang, L Qiao, Y Zhang, H Bei, HM Christen, RE Stoller, and L Wang. 2016. “Direct Observation of Defect Range and Evolution in Ion-Irradiated Single Crystalline Ni and Ni Binary Alloys.” Scientific Reports 6:19994. DOI: 10.1038/srep19994

Zhang Y, GM Stocks, K Jin, C Lu, H Bei, BC Sales, L Wang, LK Béland, RE Stoller, GD Samolyuk, M Caro, A Caro, and WJ Weber. 2015. “Influence of Chemical Disorder on Energy Dissipation and Defect Evolution in Concentrated Solid Solution Alloys.” Nature Communications 6:8736. DOI: 10.1038/ncomms9736

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.