Title: Irradiation effects on geopolymers and additively manufactured 316H stainless steel
Advisors: Professor Iwona Jasiuk, Chair, Director of Research
Professor John Popovics, Co-Chair
Abstract
This Ph.D. dissertation research investigated three classes of materials designed for extreme environments. They include metakaolin-based geopolymers for nuclear shielding, additively manufactured (AM) 316H stainless steel (SS) for radiation resistance, and equine hoof walls serving as bioinspiration for impact-resistant materials designs.
First, we explored a potassium-based geopolymer implanted with Ti+ ions to simulate neutron irradiation as a concrete alternative for nuclear facilities. Post-irradiation, the geopolymer showed a 90% increase in microhardness, a 46% rise in reduced modulus, and a 23% decrease in contact depth. Surface cracking was observed, attributed to ion implantation and reduced water content, highlighting its potential for shielding applications with further optimization.
Next, we studied the irradiation response of AM 316H SS, produced via laser powder bed fusion, compared to conventionally manufactured SS under simulated irradiation conditions using 0.5 MeV H+ ions. Multiscale characterization showed AM SS exhibited higher initial dislocation densities, reduced microstrain at lower doses (0.6 dpa), and more stable mechanical behavior under irradiation than conventional SS. Microhardness testing revealed a gradual response in AM SS, while tensile tests indicated reduced hardening and strength. The surface analysis highlighted distinct pore morphologies and stable elemental composition in AM SS, contrasting the significant surface deterioration in conventional SS. These findings demonstrate AM 316H SS's superior microhardness, microstructural integrity, and radiation resistance, underscoring its suitability for irradiated environments. Molecular dynamics simulations allowed to explore the influence of porous microstructures on AM 316H SS's radiation resistance. By investigating varying pore configurations (1 to 30,720 pores) and primary knock-on atom (PKA) energies (5, 10, and 15 keV), this modeling revealed that defect numbers increased significantly with higher pore counts. The 6-pore configuration exhibited optimal irradiation resistance, while high pore densities altered dislocation mechanisms. The results provide critical insights into the enhanced radiation resistance observed in AM materials.
Finally, we investigated equine hoof walls using micro-computed tomography (μ-CT) and serial block-face scanning electron microscopy (SBF-SEM). The discovery of nano-sized pores within the tubule wall explained higher porosity values observed via helium pycnometer. This characterization of the hoof wall structure can inform the design of energy-absorbing materials.
This dissertation advances the understanding of materials’ behavior under extreme conditions, offering insights into radiation-resistant materials and bioinspired designs for improved performance in nuclear and structural applications.