Melting the alloy

Is order always better than mess? – research on disordered metal alloys as a chance for safer nuclear and thermonuclear reactors



Krzysztof Petelczyc

Entropy is a measure of disorder. One of the fundamental laws of physics indicates that it increases when the system consists of several different elements of equal or similar concentration. Therefore, the current model for developing new materials was based on the assumption that the alloy should have low entropy, i.e. have one leading element that is responsible for the most important properties of the material. It turns out, however, that high entropy in metal alloys combined with the distortion of the atomic lattice contributes to improving the functional properties of the material and not, as previously believed, to their deterioration. These surprising phenomena will be investigated by an international team of scientists led by prof. Łukasz Kurpaska as part of the project "Production of high-entropy alloys with high radiation resistance and increased mechanical properties at high temperature" financed by the National Science Center under the SONATA BIS program.

Generation IV nuclear reactors as well as fusion (thermonuclear) reactors, require special construction materials with excellent mechanical properties at high temperatures and good resistance to radiation damage and corrosion. These stringent requirements seem to be met by the so-called high entropy alloys (HEA). However, it is not entirely known why they have such unique properties and what determines them. Moreover, HEAs are currently produced only in laboratories, and more R&D is necessary to verify the possibility of their industrial production. Therefore, scientists from the National Centre for Nuclear Research want to develop a technique for producing this new type of materials and understand the mechanisms responsible for their excellent functional properties at high temperatures. For this reason, experimental tests and simulations will be carried out in conditions imitating the operation of a nuclear reactor. 

“The project will produce and test various types of alloys with controlled amounts of chromium, nickel, iron, and manganese.” – explains prof. Kurpaska. – “We want to investigate the impact of the complexity of the chemical composition by progressively changing it. Research will begin on binary (NiFe) and ternary (NiFeCr) systems. It is expected that the work will be completed on at least four-component alloys (NiFeCrMn), perhaps with the addition of other elements such as Al.” Understanding and optimizing the chemical composition may enable the description of the evolution of defects created during radiation damage. Explaining this phenomenon will contribute to the increase in the so-called lifetime of materials working in the environment of a nuclear reactor.

In order to produce new materials, the alloys will be subjected to appropriate thermal treatment and cold rolling. The resulting materials will be tested both in their initial state and after bombardment with heavy ions at high temperatures. Advanced mechanical and structural tests and numerical simulations will be carried out, leading to answers related to the plasticity of these materials and other unique properties, such as migration and defect evolution. In accordance with the assumptions of the SONATA BIS program, the idea of the project is the cooperation not only of experimentalists specializing in structural and mechanical tests, but also of experienced scientists dealing with numerical simulations. The research work will be carried out jointly by scientists from the National Center for Nuclear Research and the American Massachusetts Institute of Technology. Prof. Kurpaska gained access to the ion accelerator located at the Department of Nuclear Science and Engineering thanks to the NAWA Bekker scholarship. Experiments simulating the influence of the neutron flux will be carried out together with scientists from this institution.

The project will, therefore, contribute to the creation of a young research group that will be able to create a path to better understand still open issues regarding newly developed high-entropy alloys. All this will be carried out in the spirit of innovation and complementarity, based on the foundations of current (NOMATEN Center of Excellence) and future joint projects.

Implementing the project will allow us to answer at least a few very important questions - Prof. Kurpaska sums up - Is it possible to successfully produce high-entropy alloys? What is the influence of the chemical composition on the structure of the material and its resistance to radiation damage? How does microstructure affect mechanical properties? It should be emphasized that all research will be carried out on modern equipment purchased by the National Center for Nuclear Research and installed at the NOMATEN Center of Excellence and the Material Research Laboratory.

We are looking forward to the results.