Charles Hirst

experiment to a single set of irradiation parameters (e.g., dose, fluence, injection rate, temperature etc.). Despite being capable of achieving damage rates up to three orders of magnitude higher than neutron irradiation, its overall sample throughput remains low due to the need to conduct separate irradiations for each unique parameter set. To address these limitations, a novel capability has been developed at the Michigan Ion Beam Laboratory (MIBL), enabling for the creation of two-dimensional lateral ion implantation gradients using recently installed motorized-controlled ion beam shutters. This advancement can generate a wide scope of the two dimensional (H+, He2+) implantation parameter space within a single sample. Integration of this new capability enables dual- and triple-ion beam experiments to be performed with full user control over not only the ion implantation depth profile, but also over the lateral imposed concentration gradients, thus providing researchers with a high-throughput means for material testing under various irradiation conditions. Furthermore, the recent installation of a microbeam in the ion-beam analysis (IBA) target station now allows for probing these concentration gradients in irradiated alloys with unprecedently high spatial resolutions. These developments promise to significantly improve ion irradiation capabilities, offering researchers a robust and high-throughput method to efficiently investigate candidate alloys for both advanced fission and fusion reactor applications, in both a time- and cost-effective manner. This paper demonstrates all the above through showcasing detailed implantation profiling and swelling characterization conducted over the lateral gradients imposed on single crystal Si and the fusion candidate alloy F82H-IEA.

Understanding how irradiation-induced defects evolve at elevated temperatures is of critical importance to predicting materials’ behavior under steady-state and accident scenarios. However, such mechanistic insight into microstructural evolution is limited by the nature of ex situ annealing and subsequent imaging. Here we show direct observation and quantification of defect recovery in neutron-irradiated Ti using in situ transmission electron microscopy (TEM) annealing experiments. In agreement with our prior work, and at temperatures below the irradiation temperature (T𝑖𝑟𝑟 = 300 ◦C), dislocation loops are observed to glide. At elevated temperatures (>500 ◦C), dislocation lines become mobile and promote significant recovery of the microstructure. These mechanisms challenge the established electron irradiation-based model for radiation damage recovery, which originally suggests dissolution of static defect clusters, and demonstrates the importance of iin situ characterization in understanding defect evolution in irradiated materials.

With full knowledge of a material’s atomistic structure, it is possible to predict any macroscopic property of interest. In practice, this is hindered by limitations of the chosen characterization techniques. For example, electron microscopy is unable to detect the smallest and most numerous defects in irradiated materials. Instead of spatial characterization, we propose to detect and quantify defects through their excess energy. Differential scanning calorimetry of irradiated Ti measures defect densities five times greater than those determined using transmission electron microscopy. Our experiments also reveal two energetically distinct processes where the established annealing model predicts one. Molecular dynamics simulations discover the defects responsible and inform a new mechanism for the recovery of irradiation-induced defects. The combination of annealing experiments and simulations can reveal defects hidden to other characterization techniques and has the potential to uncover new mechanisms behind the evolution of defects in materials.