Understanding self-assembled He-bubble superlattices under deformation in materials utilizing novel experimental methods

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Non-technical abstract:The creation of inert gases in materials, by nuclear reactions induced by irradiation within a material, for example, can lead to the development of very small gas bubbles in the material. These features can change a material's response to mechanical deformation and can lead to increased strength. Depending on temperature, the amount of gas, and time, these gas bubbles can arrange themselves into an ordered structure, which is oftentimes called a gas-bubble 'superlattice'. Deformation of the material, can change the arrangement of this gas-bubble superlattice, which, in turn, can change the mechanical-property response of the material. In this work, we will focus on helium (He) bubbles, which are common in materials exposed to nuclear environments. We will use a helium-ion-beam microscope with subsequent small-scale mechanical-property evaluation techniques, such as indentation and nano-pillar compression testing. Different materials which represent different structures will be investigated which will allow us to understand the changes these structures undergo while being deformed and its implications for the mechanical performance of a material. The images and results of this research will be used as an outreach tool in classes and in presentations, to engage local high-school students in materials research. Furthermore, we will actively engage undergraduate students, especially those from underrepresented minority groups, in this research effort, thereby training them on relevant materials-science techniques and tools and preparing them early for graduate school.Technical abstract:This program aims to obtain a fundamental understanding of self-assembled, nanoscale, He-bubble superlattices in representative metallic materials of different crystal structures under external load and subsequent deformation. The goal is to observe how this regular arrangement of gas bubbles reacts to the deformation, perhaps even to the point of losing the regular arrangement of the bubbles. To make these observations systematically, we will utilize a He-ion-beam microscope in a novel way: namely, not to photograph images but to implant the beam's He into the material. By controlling the implantation, we can quantify with increased experimental accuracy the mechanical-property changes associated with these structures, which will allow us to refine the material-hardening models with direct parameter input from these experiments. Expanding the experimental text matrix to different crystal structures (FCC, BCC, HCP) will lead to a more fundamental understanding of the formation of these structures while also generalizing the effect of these structures on mechanical properties. Additionally, the development of this new implantation technique not only will accelerate research on gas bubbles in materials but may also impact other scientific fields investigating the optical and quantum properties of semiconductors as well as nano-foamed materials. The funding will provide the resources needed to do the research and will allow the nuclear-materials group at UC Berkeley to intensify our outreach efforts both within and outside the academic community, to trigger the general public's interest in materials and nanoscience.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.