Congratulations to Dr. Emily Hopkins Mang on successfully defending her thesis, entitled “Dynamic Insight to Radiation-Induced Defect Accommodation in Pure Metals and Refractory Alloys”. Check out the abstract, below! Congratulations, Emily! We can’t wait to see what you do next!
Abstract: Accelerating energy demands and climate change concerns have driven research toward developing radiation-tolerant materials to extend the life of existing nuclear reactors and enable advanced reactor designs. In nuclear environments, structural materials inevitably accumulate irradiation-induced defects, leading to degradation and eventual failure. Two promising damage mitigation strategies include (i) tailoring grain boundary (GB) structures to enhance point-defect recombination, and (ii) employing compositionally complex alloys (CCAs), whose lattice distortions and varied energy landscapes may suppress defect formation and promote thermal stability.
Under irradiation, GBs can become metastable as their structure evolves, developing unique absorption capacities in their non-equilibrium state. This inherent metastability may enable dynamic self-healing properties, though it is difficult to observe experimentally, particularly in CCAs where complicated crystalline matrix effects will likely dominate defect evolution processes. Using in situ and ex situ ion irradiation experimentation and analytical transmission electron microscopy (TEM), this dissertation will investigate the interplay between GB structural metastability, alloy chemical complexity and irradiation-induced defect morphology evolution. Systems studied range from pure metals and dilute alloys to multi-principal element systems. Computer vision and deep-learning object detection is demonstrated on in situ ion irradiation datasets to extract temporally resolved microstructural data, enabling quantification of defect densities, sizes, and spatial distributions.
In pure Cu, in situ observations reveal that evolving GB elastic environments influence microstructural defect retention. Multiscale modeling supports evaluation of metastable GB properties that modulate nearby defect concentrations and GB elasticity. The work transitions to complex alloys, where irradiation responses differ against their dilute counterparts, showing suppression of helium bubble agglomeration and modified dislocation evolution mechanisms driven by solute interactions. In situ experiments demonstrate that chemical complexity modifies dislocation loop mobility, size distribution, and stability, with direct evidence of lattice distortion-induced dislocation pinning in CCAs. The work challenges assumptions about the effectiveness of CCA GBs in radiation damage mitigation compared to dilute alloys and explores how high-temperature and helium irradiation induce structural instabilities in CCAs promoting the formation of intragranular substructures. Collectively, this work aims to provide new mechanistic insight into GB-mediated defect accommodation and refine perspectives of chemistry-driven radiation responses in complex alloys.
