Collaborative Research: Interface enabled plasticity in high-strength Co-based intermetallics

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Nontechnical SummaryThe design of high strength and high deformability materials is critical for next-generation structural applications that can transform the national defense systems and industries such as aerospace, automotive, and energy. Intermetallics, with their remarkable properties of high mechanical strength and high melting temperatures, are excellent candidates for these applications. However, conventional intermetallics are very brittle at room temperature, which adversely impacts their potential as structural materials. Although intermetallics have been the subject of active research in recent decades, achieving room temperature plasticity while retaining high strength has been a major challenge. Prior approaches to improve plasticity in intermetallics have primarily focused on improving fracture resistance by grain refinement, improving grain boundary cohesive strength and introducing second phase particles. The investigators’ preliminary studies reveal that CoAl nanocomposites with unconventional thick grain boundaries exhibit ultra-high strength and high deformability. However, the fundamental mechanisms underpinning these remarkable properties remain unclear. Through the synergistic combination of nanofabrication, in situ nanomechanical testing and atomistic modeling, they elucidate the deformation mechanisms in core/shell nanocomposites at an atomistic level. The close collaboration among the investigators enable graduate and undergraduate research students to develop a wholesome foundation in both experiments and simulations through biweekly videoconferences, and annual visits to counterpart institutions. Graduate students also access advanced microscopy facilities housed within the Center for Integrated Nanotechnologies managed by Los Alamos National Lab and Sandia National Lab. The investigators recruit minority students for the proposed project. The specimens fabricated from this project are tested at NASA’s International Space Station. Technical SummaryThe goal of this project is to understand the mechanical behavior of nanocrystalline (NC) intermetallics with a novel core/shell architecture that endows them with simultaneous high strength and unprecedented deformability at room temperature. The investigators explore the deformation mechanisms in core/shell composites via integrated in situ nanoindentation and atomistic simulations to elucidate grain boundary dominated plasticity in nanocrystalline intermetallics, quantify the impact of thick interfaces on strengthening and deformability of CoAl intermetallics in core/shell nanocomposites, and understand the high temperature deformation mechanisms of core/shell nanocomposites by combining in situ microcompression tests in SEM and molecular dynamics simulations. The research program significantly advances the understanding of the deformation mechanisms, design and fabrication of intermetallics with unconventional core/shell architecture for critical structural applications. This work furnishes atomistic insights into “thick” grain boundary as novel motifs for extraordinary mechanical properties that open up avenues for the rational design of other intermetallics through grain boundary engineering.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.