Fracture and Stability of Metallic Nanotwinned Structures

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TECHNICAL SUMMARY: Research over the past few years has provided compelling evidence for the extraordinary properties of nanotwinned metals as compared to their nanocrystalline and fine-grained counterparts. Some of these enhanced properties include ultra-high yield strength, high ductility, good electrical conductivity, and high strain rate sensitivity. Such characteristics make nanotwinned metals highly attractive materials for structural applications. The aim of this project is to provide quantitative insight into the stability and fracture mechanisms in nanotwinned metals by way of a focused experimental and computational modeling effort. These critical issues, if unaddressed, would limit the practical application of these nanostructured metals and alloys, largely due to concerns over the achievement and stability of optimal properties. To this end, the specific objectives of the project are to investigate the role of twin boundaries in the brittle versus ductile response of nanotwinned metals and to study twin boundary-mediated processes such as twin-twin interactions and crack/defect nucleation at twin boundaries, in order to predict the critical twin lamella thickness for optimal performance of nanotwinned metals.NON-TECHNICAL SUMMARY: The proposed research is expected to have an impact on several important areas of nanostructured metal science and technology by way of providing valuable insight into the deformation mechanisms governing their behavior. In particular, it will provide a quantitative understanding into the optimal structural performance of nanocrystalline and nanotwinned metals, with regards to critical issues such as strength, ductility, stability, and fracture mechanisms. The ultimate goal of this unified experimental, modeling and manufacturing effort is the development of processing routes for bulk synthesis of nanotwinned metals, which would realize their potential as next generation structural materials. The proposed research would also contribute to the enrichment of the community through education and outreach efforts. Graduate and undergraduate students working on the project, would develop a strong foundation in the multidisciplinary areas of nanomechanics and computational materials science. In addition, the scientific advances made through this project would be integrated into the coursework developed by the investigators at their institutions.