Ph.D. topics

Ion Irradiation and Materials Characterization of Novel Refractory HEAs for Nuclear Applications

Ph. D. student

Anwesha Karmakar

Supervisor

Prof. Dr.-Ing. Thomas Weissgärber (TUD), Dr. Cornelia Kaden (HZDR)

Department

Structural Materials

Period

03/2026 - 02/2029

Project HELENA

Overview

To meet the harsh demands of Gen-IV fission and fusion reactors, the BMFTR-funded project HELENA explores body-centered-cubic (BCC) refractory high-entropy alloys (RHEAs) as next-generation structural materials. In collaboration with Technische Universität Dresden (TUD) and Fraunhofer IFAM Dresden, a Cr-Fe-Ti-V-W-Zr-based refractory high entropy alloy (RHEA) system will be designed using CALPHAD simulations and fabricated by powder metallurgy. This theses contributes to the project by investigating the irradiation tolerance and long-term microstructure stability of the developed alloys. Through ion irradiation as an accelerated proxy for neutron damage, combined with thermal aging studies up to 700°C, the evolution of radiation-induced defects, phase stability, and irradiation-induced hardening will be assessed and benchmarked against established and emerging candidate alloys. The results will provide critical insight into the suitability of RHEAs for future nuclear applications.

Motivation

Nuclear energy represents a highly cost-effective, low-carbon component of the global energy mix. To maximize the long-term sustainability, safety and efficiency of nuclear power, advanced Generation-IV (Gen-IV) fission reactors and fusion concepts are under development. These technologies impose unprecedentedly harsh operational environments for materials, including high temperatures, severe corrosive environments, and intense neutron irradiation over extended service lifetimes.

To address these challenges, the project investigates body-centered-cubic (bcc) refractory high entropy alloys (RHEAs), as a promising class of irradiation-tolerant alloys. The high-entropy-alloy (HEA) design concept based on multiple principal alloying elements to stabilize simple solid-solution phases, offers a promising pathway toward achieving a combination of high-temperature strength, phase stability, and irradiation tolerance. These attributes make RHEA attractive for future nuclear systems.

In collaboration with TUD and IFAM, the project explores alloy systems based on, but not limited to, the Cr-Fe-Ti-V-W-Zr compositional space. CALPHAD-based thermodynamic simulations will be utilized to guide alloy design. Selected alloys will be synthesized by IFAM and characterized with respect to baseline properties. These activities build the foundation for this thesis.

Our focus

The primary focus of this thesis is the assessment of the irradiation tolerance and long-term microstructural stability. To efficiently simulate neutron-induced damage, ion irradiation is employed as an accelerated proxy. Unlike neutron exposure, which renders materials highly radioactive and logistically difficult to analyze, ion beams allow for accelerated high-levels of displacement damage in a significantly shorter timeframe without activating the samples.

Thermal aging experiments at high temperatures up to 700°C will be implemented to evaluate phase stability. Post-irradiation and post-aging degradation are characterized using state-of-the-art analytical tools, including Transmission Electron Microscopy (TEM). Nanoindentation is deployed to track mechanical property changes, particularly irradiation-induced hardening.

To assess the potential of the developed RHEA, their performance will be benchmarked against established and emerging structural material candidate alloys for fusion and fission application. By correlating alloy composition, microstructure, irradiation response and mechanical properties, this work aims to establish key composition-microstructure-property relationships that will guide the development of advanced irradiation-tolerant nuclear materials.

This research is funded by the German Federal Ministry of Research, Technology and Space (Bundesministerium für Forschung, Technologie und Raumfahrt - BMFTR), grant number 02NUK100A.