GOALI: Friction Stir Joining of Bulk Metallic Glasses and Their Composites

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Bulk metallic glasses are a relatively new class of engineering materials with a combination of exceptional properties and unique processing ability. Their high strength, elasticity, corrosion resistance and soft magnetic properties make them attractive for a range of military, medical, sporting, and industrial applications. However, joining of metallic glasses remains a major challenge across multiple length-scales. This Grant Opportunity for Academic Liaison with Industry (GOALI) research will use a solid-state joining approach to achieve large sections of bulk metallic glasses with superior surface properties. Use of these structures as bio-implants could potentially lessen the likelihood of tissue inflammation, bone deterioration and replacement surgeries thus advancing national health and welfare. Use of stacked metallic glasses as penetrator shields on armor vehicles and spacecraft protection against orbital debris impacts will significantly advance the national defense interests. The proposed project will be collaborative in many aspects, with active engagement between the academic and industrial partners, including an industry internship for two graduate students funded by the project. It will provide a rare opportunity for students to integrate classroom concepts with industrial research and development. The project will engage students from underrepresented groups and will contribute to educating the next generation of scientists/engineers in advanced manufacturing. The project will also benefit society by exposing K-12 students and teachers to emerging areas in science and technology.The research objective of this GOALI project is to achieve fundamental scientific understanding of friction stir joining process for amorphous metallic alloys and their composites by an integrated experimental and modeling approach. The research project will build on promising preliminary experiments to connect the understanding of material flow in adjoining layers during friction stir joining process, multi-scale deformation behavior, molecular dynamics simulations, and large-scale finite element modeling. The unique and fundamental scientific contributions resulting from the proposed work will be four fold. Firstly, the research will advance knowledge of shear mixing and metallurgical bond formation during high strain processing of amorphous metals and composites. Secondly, it will enable understanding of deformation mechanisms resulting from the interaction of different microstructural features. Third part involving atomistic-scale models will create knowhow on free volume evolution in response to high strain. Lastly, the proposed research will help in the development of a framework to predict location specific properties consisting of spatially resolved structure evolution from the temperature, cooling rate, and strain distribution. The main innovation of the proposed research lies in achieving homogeneous and stacked structures of amorphous metals that are unattainable using existing technologies with the hypothesis that intense shear mixing at the interface between amorphous metallic components ruptures the surface oxide resulting in pristine metal flow and metallurgical bonding. The high strain during processing is expected to increase atomic-scale inhomogeneity in metallic glasses leading to rejuvenation and markedly improved mechanical properties compared to cast amorphous structures.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.