A novel high-throughput method for quantification of materials swelling via microscale dilation techniques

Material swelling is a key microstructural degradation pathway during irradiation. Swelling occurs due to conglomeration of radiation-induced vacancies into microscale cavities, ultimately changing a material’s geometry. Swelling is of particular concern for advanced reactors, where high temperatures (>300°C) and damage levels (>50 dpa) often leads to a steady state material swelling rate of ~1 percent swelling per dpa. A material’s swelling response is typically determined by irradiating samples (with ions or neutrons), then utilizing focused ion beam (FIB) milling to prepare an electron-transparent microscopy sample. One major limitation of this technique is the cost & time necessary to prepare electron-transparent samples, collect a variety of high-quality cavity images, and accurately index each cavity. Furthermore, the small volume of an electron-transparent sample (< 1 μm3) necessitates that multiple samples per experimental conditions (material and irradiation) must be analyzed to reach statistical significance. Other methods to determine the swelling response of a material have been developed, such as the mask/unmasked step-height technique. However, this technique does not work with neutron experiments and does not induce isotropic swelling in the microstructure.

The main outcome of this proposal will be the demonstration of a novel high-throughput method for quantification of materials swelling via microscale dilation techniques. This technique will use pre-irradiation FIB milling to prepare irradiation samples with arrays of micropillars throughout the sample surface. Post-irradiation, the dilation and elongation of these micropillars will be quantified using rapid scanning-electron microcopy (SEM) imaging and the swelling response determined. As these micropillars are significantly larger than electron-transparent samples and there is no need to index individual cavities, these swelling responses will have improved statistical confidence and be fast/cheaper to determine than other techniques used today. This technique will also work with neutron irradiated samples and better emulate isotropic material swelling.