Optimizing Materials Design for Irradiation Endurance through Structural and Chemical Modifications

Abstract

The optimization of material performance remains a critical challenge in high-radiation environments. Recently, high entropy materials (HEMs) have ushered in an era of opportunity for materials design in extreme conditions. The term "HEMs" refers to materials that exhibit a substantial contribution of configurational entropy to Gibbs free energy. To date, various classes of HEMs, including high entropy alloys (HEAs), high entropy ceramics (HECs), and high entropy nanoparticles, have been explored. Among these, HEAs have received extensive attention over the past two decades. Research has demonstrated that incorporating multiple principal elements can significantly enhance material properties, resulting in unprecedented performance, such as improved irradiation resistance, mechanical strength, and corrosion resistance.

In contrast to conventional alloys, HEAs are characterized by their pronounced lattice distortion and chemical complexity, which lead to enhanced electron scattering, reduced thermal conductivities, and stronger electron-phonon (e-ph) coupling. These features are expected to facilitate Frenkel pair (FP) recombination, delayed damage accumulation, and suppressed cluster growth. This thesis investigates strategies to optimize material design for irradiation endurance through structural and chemical engineering, with a particular focus on HEAs and related multi-component materials. By systematically examining the role of local lattice distortions, chemical ordering/disordering, and interfaces between chemically disordered and ordered phase, novel approaches to mitigating irradiation-induced damage and preserving material integrity were explored.

The study begins by examining the role of lattice distortions in enhancing irradiation tolerance in concentrated solid solution alloys (CSAs). The introduction of large solute atoms into the matrix induces severe lattice distortions, which act as effective traps for defects, preventing the migration of interstitials and vacancies. This approach is exemplified by the binary Ni₈₀Mo₂₀ alloy, which demonstrates a marked reduction in the size and density of defect clusters due to its unprecedented local lattice distortion. These findings suggest that strategic engineering of lattice distortions can significantly improve irradiation resistance.

Beyond lattice distortions, the research investigates the role of chemical ordering modulation in multi-component alloys. By systematically tuning local chemical order (LCO) in CSAs, it is demonstrated that defect dynamics follow chemically biased diffusion pathways, leading to controllable defect evolution behaviors. The degree of chemical disorder and the spatial extent of ordered regions emerge as key factors influencing defect clustering and annihilation. These results highlight the critical role of microstructural control in designing irradiation-resistant materials.

Further, the study explores the effects of coupled disorder-order, focusing on the chemically complex L1₂ γ' Ni₃Al intermetallic phase, which serves as a crucial strengthening component in HEAs. Under irradiation, the γ' phase is prone to disordering, thereby compromising its strengthening effect. By incorporating elements such as Ti and Co, the kinetic reordering capacity of the γ' phase is enhanced, mitigating irradiation-induced disorder and preserving its structural integrity. This research underscores the importance of chemical composition design in maintaining the long-term performance of high-strength HEAs at elevated temperatures.

Finally, the study examines the role of interfaces between disordered and ordered phases in defect evolution, using γ/γ' interfaces as a model system. The results reveal that increasing interfacial mismatch promotes FP recombination at the interface. However, the intrinsic chemical complexity of HEAs introduces disorder within the L1₂ γ' phase, generating a complex energy landscape at the interface. While this disorder reduces the conventional defect-sink efficiency of the interface, it also presents alternative pathways for defect evolution, suggesting new mechanisms beyond classical mismatch-driven models.

In conclusion, this thesis presents a comprehensive approach to material design for irradiation environments, utilizing atomic-scale modifications to achieve macroscopic performance improvements. The research offers innovative strategies for developing materials with enhanced irradiation tolerance, paving the way for advanced applications in nuclear engineering.

Date of Award	9 Jul 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shijun ZHAO (Supervisor)