The challenging operating environments of advanced nuclear fission and fusion reactors require the development of new robust materials. These new materials must survive increased physical, chemical, thermal, and radiation-related challenges. High-entropy alloys (HEAs) have displayed notable mechanical, thermomechanical, and corrosion-resistant properties, and in addition, there is ample unexplored compositional space that enables the development of new materials. Furthermore, research has shown that HEAs may exhibit distinctive irradiation tolerance, including reduced defect production and resistance to irradiation-induced swelling and hardening.
Advanced materials are key to the development of reliable, sustainable, and efficient nuclear reactors. Generation IV (Gen-IV) fission and proposed fusion reactor designs will operate under extreme conditions. Reactor components are expected to experience temperatures up to and exceeding 1000 °C and larger neutron fluences than seen in current reactors. In addition, fusion reactors have the extra challenge of first-wallmaterials being exposed to a high-flux plasma. Plasma irradiation of material creates a dynamic surface with a changing interface and changing surface morphology and chemistry. It has previously been demonstrated that low energy (~20 eV) helium ions can greatly affect the material surface, reduce thermal conductivity, and can lead to significant nano-structuring of the material. The level to which both surface morphology and sub-surface defects caused by the plasma-material interaction influence the diffusion, trapping, and precipitation of hydrogen isotopes and helium species into gas bubbles is an outstanding question. It has recently been shown that He-bubble formation in the near-surface region can have a strong effect on the recrystallization kinetics of tungsten, leading to effectively retarding the recrystallization process and the accompanying grain growth process. In addition, changes in the thermal and mechanical properties were observed down to a few microns below the surface (i.e., far beyond the implantation depth) after plasma exposure.
The overarching goal of the proposed research is to improve our ability to predict the performance of HEA materials subjected to helium plasma exposure by understanding and untangling the effects of plasma fluences and temperature change and applying this knowledge to materials in extreme environments (e.g., nuclear reactor and space).